Merge remote-tracking branch 'remotes/dgilbert-gitlab/tags/pull-virtiofs-20201026' into staging

virtiofsd pull 2020-10-26

Misono
   Set default log level to info
   Explicit build option for virtiofsd

Me
   xattr name mapping

Stefan
  Alternative chroot sandbox method

Max
  Submount mechanism

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

# gpg: Signature made Mon 26 Oct 2020 18:41:36 GMT
# gpg:                using RSA key 45F5C71B4A0CB7FB977A9FA90516331EBC5BFDE7
# gpg: Good signature from "Dr. David Alan Gilbert (RH2) <dgilbert@redhat.com>" [full]
# Primary key fingerprint: 45F5 C71B 4A0C B7FB 977A  9FA9 0516 331E BC5B FDE7

* remotes/dgilbert-gitlab/tags/pull-virtiofs-20201026:
  tests/acceptance: Add virtiofs_submounts.py
  tests/acceptance/boot_linux: Accept SSH pubkey
  virtiofsd: Announce sub-mount points
  virtiofsd: Store every lo_inode's parent_dev
  virtiofsd: Add fuse_reply_attr_with_flags()
  virtiofsd: Add attr_flags to fuse_entry_param
  virtiofsd: Announce FUSE_ATTR_FLAGS
  linux/fuse.h: Pull in from Linux
  tools/virtiofsd: xattr name mappings: Simple 'map'
  tools/virtiofsd: xattr name mapping examples
  tools/virtiofsd: xattr name mappings: Map server xattr names
  tools/virtiofsd: xattr name mappings: Map client xattr names
  tools/virtiofsd: xattr name mappings: Add option
  virtiofsd: add container-friendly -o sandbox=chroot option
  virtiofsd: passthrough_ll: set FUSE_LOG_INFO as default log_level
  configure: add option for virtiofsd

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

17 files changed, 1528 insertions, 40 deletions

diff --git a/configure b/configure
index 55e07c82dd..83610b0db8 100755
--- a/configure
+++ b/configure
@@ -302,6 +302,7 @@ fdt="auto"
 netmap="no"
 sdl="auto"
 sdl_image="auto"
+virtiofsd="auto"
 virtfs=""
 libudev="auto"
 mpath="auto"
@@ -999,6 +1000,10 @@ for opt do
   ;;
   --enable-libudev) libudev="enabled"
   ;;
+  --disable-virtiofsd) virtiofsd="disabled"
+  ;;
+  --enable-virtiofsd) virtiofsd="enabled"
+  ;;
   --disable-mpath) mpath="disabled"
   ;;
   --enable-mpath) mpath="enabled"
@@ -1758,6 +1763,7 @@ disabled with --disable-FEATURE, default is enabled if available:
   vnc-png         PNG compression for VNC server
   cocoa           Cocoa UI (Mac OS X only)
   virtfs          VirtFS
+  virtiofsd       build virtiofs daemon (virtiofsd)
   libudev         Use libudev to enumerate host devices
   mpath           Multipath persistent reservation passthrough
   xen             xen backend driver support
@@ -6972,7 +6978,7 @@ NINJA=$ninja $meson setup \
         -Dxen=$xen -Dxen_pci_passthrough=$xen_pci_passthrough -Dtcg=$tcg \
         -Dcocoa=$cocoa -Dmpath=$mpath -Dsdl=$sdl -Dsdl_image=$sdl_image \
         -Dvnc=$vnc -Dvnc_sasl=$vnc_sasl -Dvnc_jpeg=$vnc_jpeg -Dvnc_png=$vnc_png \
-        -Dgettext=$gettext -Dxkbcommon=$xkbcommon -Du2f=$u2f \
+        -Dgettext=$gettext -Dxkbcommon=$xkbcommon -Du2f=$u2f -Dvirtiofsd=$virtiofsd \
         -Dcapstone=$capstone -Dslirp=$slirp -Dfdt=$fdt \
         -Diconv=$iconv -Dcurses=$curses -Dlibudev=$libudev\
         -Ddocs=$docs -Dsphinx_build=$sphinx_build -Dinstall_blobs=$blobs \
diff --git a/docs/tools/virtiofsd.rst b/docs/tools/virtiofsd.rst
index 7ecee49834..34a9e40146 100644
--- a/docs/tools/virtiofsd.rst
+++ b/docs/tools/virtiofsd.rst
@@ -17,13 +17,24 @@ This program is designed to work with QEMU's ``--device vhost-user-fs-pci``
 but should work with any virtual machine monitor (VMM) that supports
 vhost-user.  See the Examples section below.
 
-This program must be run as the root user.  Upon startup the program will
-switch into a new file system namespace with the shared directory tree as its
-root.  This prevents "file system escapes" due to symlinks and other file
-system objects that might lead to files outside the shared directory.  The
-program also sandboxes itself using seccomp(2) to prevent ptrace(2) and other
-vectors that could allow an attacker to compromise the system after gaining
-control of the virtiofsd process.
+This program must be run as the root user.  The program drops privileges where
+possible during startup although it must be able to create and access files
+with any uid/gid:
+
+* The ability to invoke syscalls is limited using seccomp(2).
+* Linux capabilities(7) are dropped.
+
+In "namespace" sandbox mode the program switches into a new file system
+namespace and invokes pivot_root(2) to make the shared directory tree its root.
+A new pid and net namespace is also created to isolate the process.
+
+In "chroot" sandbox mode the program invokes chroot(2) to make the shared
+directory tree its root. This mode is intended for container environments where
+the container runtime has already set up the namespaces and the program does
+not have permission to create namespaces itself.
+
+Both sandbox modes prevent "file system escapes" due to symlinks and other file
+system objects that might lead to files outside the shared directory.
 
 Options
 -------
@@ -69,6 +80,13 @@ Options
   * readdirplus|no_readdirplus -
     Enable/disable readdirplus.  The default is ``readdirplus``.
 
+  * sandbox=namespace|chroot -
+    Sandbox mode:
+    - namespace: Create mount, pid, and net namespaces and pivot_root(2) into
+    the shared directory.
+    - chroot: chroot(2) into shared directory (use in containers).
+    The default is "namespace".
+
   * source=PATH -
     Share host directory tree located at PATH.  This option is required.
 
@@ -109,6 +127,167 @@ Options
   timeout.  ``always`` sets a long cache lifetime at the expense of coherency.
   The default is ``auto``.
 
+xattr-mapping
+-------------
+
+By default the name of xattr's used by the client are passed through to the server
+file system.  This can be a problem where either those xattr names are used
+by something on the server (e.g. selinux client/server confusion) or if the
+virtiofsd is running in a container with restricted privileges where it cannot
+access some attributes.
+
+A mapping of xattr names can be made using -o xattrmap=mapping where the ``mapping``
+string consists of a series of rules.
+
+The first matching rule terminates the mapping.
+The set of rules must include a terminating rule to match any remaining attributes
+at the end.
+
+Each rule consists of a number of fields separated with a separator that is the
+first non-white space character in the rule.  This separator must then be used
+for the whole rule.
+White space may be added before and after each rule.
+
+Using ':' as the separator a rule is of the form:
+
+``:type:scope:key:prepend:``
+
+**scope** is:
+
+- 'client' - match 'key' against a xattr name from the client for
+             setxattr/getxattr/removexattr
+- 'server' - match 'prepend' against a xattr name from the server
+             for listxattr
+- 'all' - can be used to make a single rule where both the server
+          and client matches are triggered.
+
+**type** is one of:
+
+- 'prefix' - is designed to prepend and strip a prefix;  the modified
+  attributes then being passed on to the client/server.
+
+- 'ok' - Causes the rule set to be terminated when a match is found
+  while allowing matching xattr's through unchanged.
+  It is intended both as a way of explicitly terminating
+  the list of rules, and to allow some xattr's to skip following rules.
+
+- 'bad' - If a client tries to use a name matching 'key' it's
+  denied using EPERM; when the server passes an attribute
+  name matching 'prepend' it's hidden.  In many ways it's use is very like
+  'ok' as either an explict terminator or for special handling of certain
+  patterns.
+
+**key** is a string tested as a prefix on an attribute name originating
+on the client.  It maybe empty in which case a 'client' rule
+will always match on client names.
+
+**prepend** is a string tested as a prefix on an attribute name originating
+on the server, and used as a new prefix.  It may be empty
+in which case a 'server' rule will always match on all names from
+the server.
+
+e.g.:
+
+  ``:prefix:client:trusted.:user.virtiofs.:``
+
+  will match 'trusted.' attributes in client calls and prefix them before
+  passing them to the server.
+
+  ``:prefix:server::user.virtiofs.:``
+
+  will strip 'user.virtiofs.' from all server replies.
+
+  ``:prefix:all:trusted.:user.virtiofs.:``
+
+  combines the previous two cases into a single rule.
+
+  ``:ok:client:user.::``
+
+  will allow get/set xattr for 'user.' xattr's and ignore
+  following rules.
+
+  ``:ok:server::security.:``
+
+  will pass 'securty.' xattr's in listxattr from the server
+  and ignore following rules.
+
+  ``:ok:all:::``
+
+  will terminate the rule search passing any remaining attributes
+  in both directions.
+
+  ``:bad:server::security.:``
+
+  would hide 'security.' xattr's in listxattr from the server.
+
+A simpler 'map' type provides a shorter syntax for the common case:
+
+``:map:key:prepend:``
+
+The 'map' type adds a number of separate rules to add **prepend** as a prefix
+to the matched **key** (or all attributes if **key** is empty).
+There may be at most one 'map' rule and it must be the last rule in the set.
+
+xattr-mapping Examples
+----------------------
+
+1) Prefix all attributes with 'user.virtiofs.'
+
+::
+
+-o xattrmap=":prefix:all::user.virtiofs.::bad:all:::"
+
+
+This uses two rules, using : as the field separator;
+the first rule prefixes and strips 'user.virtiofs.',
+the second rule hides any non-prefixed attributes that
+the host set.
+
+This is equivalent to the 'map' rule:
+
+::
+-o xattrmap=":map::user.virtiofs.:"
+
+2) Prefix 'trusted.' attributes, allow others through
+
+::
+
+   "/prefix/all/trusted./user.virtiofs./
+    /bad/server//trusted./
+    /bad/client/user.virtiofs.//
+    /ok/all///"
+
+
+Here there are four rules, using / as the field
+separator, and also demonstrating that new lines can
+be included between rules.
+The first rule is the prefixing of 'trusted.' and
+stripping of 'user.virtiofs.'.
+The second rule hides unprefixed 'trusted.' attributes
+on the host.
+The third rule stops a guest from explicitly setting
+the 'user.virtiofs.' path directly.
+Finally, the fourth rule lets all remaining attributes
+through.
+
+This is equivalent to the 'map' rule:
+
+::
+-o xattrmap="/map/trusted./user.virtiofs./"
+
+3) Hide 'security.' attributes, and allow everything else
+
+::
+
+    "/bad/all/security./security./
+     /ok/all///'
+
+The first rule combines what could be separate client and server
+rules into a single 'all' rule, matching 'security.' in either
+client arguments or lists returned from the host.  This stops
+the client seeing any 'security.' attributes on the server and
+stops it setting any.
+
 Examples
 --------
 
diff --git a/include/standard-headers/linux/fuse.h b/include/standard-headers/linux/fuse.h
index f4df0a40f6..7dd7a3b992 100644
--- a/include/standard-headers/linux/fuse.h
+++ b/include/standard-headers/linux/fuse.h
@@ -227,7 +227,7 @@ struct fuse_attr {
 	uint32_t	gid;
 	uint32_t	rdev;
 	uint32_t	blksize;
-	uint32_t	padding;
+	uint32_t	flags;
 };
 
 struct fuse_kstatfs {
@@ -310,6 +310,7 @@ struct fuse_file_lock {
  * FUSE_NO_OPENDIR_SUPPORT: kernel supports zero-message opendir
  * FUSE_EXPLICIT_INVAL_DATA: only invalidate cached pages on explicit request
  * FUSE_MAP_ALIGNMENT: map_alignment field is valid
+ * FUSE_ATTR_FLAGS: fuse_attr.flags is present and valid
  */
 #define FUSE_ASYNC_READ		(1 << 0)
 #define FUSE_POSIX_LOCKS	(1 << 1)
@@ -338,6 +339,7 @@ struct fuse_file_lock {
 #define FUSE_NO_OPENDIR_SUPPORT (1 << 24)
 #define FUSE_EXPLICIT_INVAL_DATA (1 << 25)
 #define FUSE_MAP_ALIGNMENT	(1 << 26)
+#define FUSE_ATTR_FLAGS		(1 << 27)
 
 /**
  * CUSE INIT request/reply flags
@@ -413,6 +415,13 @@ struct fuse_file_lock {
  */
 #define FUSE_FSYNC_FDATASYNC	(1 << 0)
 
+/**
+ * fuse_attr flags
+ *
+ * FUSE_ATTR_SUBMOUNT: File/directory is a submount point
+ */
+#define FUSE_ATTR_SUBMOUNT      (1 << 0)
+
 enum fuse_opcode {
 	FUSE_LOOKUP		= 1,
 	FUSE_FORGET		= 2,  /* no reply */
diff --git a/meson.build b/meson.build
index 835424999d..47e32e1fcb 100644
--- a/meson.build
+++ b/meson.build
@@ -2045,6 +2045,7 @@ summary_info += {'Audio drivers':     config_host['CONFIG_AUDIO_DRIVERS']}
 summary_info += {'Block whitelist (rw)': config_host['CONFIG_BDRV_RW_WHITELIST']}
 summary_info += {'Block whitelist (ro)': config_host['CONFIG_BDRV_RO_WHITELIST']}
 summary_info += {'VirtFS support':    config_host.has_key('CONFIG_VIRTFS')}
+summary_info += {'build virtiofs daemon': have_virtiofsd}
 summary_info += {'Multipath support': mpathpersist.found()}
 summary_info += {'VNC support':       vnc.found()}
 if vnc.found()
diff --git a/meson_options.txt b/meson_options.txt
index 48ab4ce7d0..b4f1801875 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -62,6 +62,8 @@ option('vnc_sasl', type : 'feature', value : 'auto',
        description: 'SASL authentication for VNC server')
 option('xkbcommon', type : 'feature', value : 'auto',
        description: 'xkbcommon support')
+option('virtiofsd', type: 'feature', value: 'auto',
+       description: 'build virtiofs daemon (virtiofsd)')
 
 option('capstone', type: 'combo', value: 'auto',
        choices: ['disabled', 'enabled', 'auto', 'system', 'internal'],
diff --git a/tests/acceptance/boot_linux.py b/tests/acceptance/boot_linux.py
index 0055dc7cee..ad997c3f2e 100644
--- a/tests/acceptance/boot_linux.py
+++ b/tests/acceptance/boot_linux.py
@@ -57,7 +57,7 @@ class BootLinuxBase(Test):
             self.cancel('Failed to download/prepare boot image')
         return boot.path
 
-    def download_cloudinit(self):
+    def download_cloudinit(self, ssh_pubkey=None):
         self.log.info('Preparing cloudinit image')
         try:
             cloudinit_iso = os.path.join(self.workdir, 'cloudinit.iso')
@@ -67,7 +67,8 @@ class BootLinuxBase(Test):
                           password='password',
                           # QEMU's hard coded usermode router address
                           phone_home_host='10.0.2.2',
-                          phone_home_port=self.phone_home_port)
+                          phone_home_port=self.phone_home_port,
+                          authorized_key=ssh_pubkey)
         except Exception:
             self.cancel('Failed to prepared cloudinit image')
         return cloudinit_iso
@@ -80,19 +81,19 @@ class BootLinux(BootLinuxBase):
     timeout = 900
     chksum = None
 
-    def setUp(self):
+    def setUp(self, ssh_pubkey=None):
         super(BootLinux, self).setUp()
         self.vm.add_args('-smp', '2')
         self.vm.add_args('-m', '1024')
         self.prepare_boot()
-        self.prepare_cloudinit()
+        self.prepare_cloudinit(ssh_pubkey)
 
     def prepare_boot(self):
         path = self.download_boot()
         self.vm.add_args('-drive', 'file=%s' % path)
 
-    def prepare_cloudinit(self):
-        cloudinit_iso = self.download_cloudinit()
+    def prepare_cloudinit(self, ssh_pubkey=None):
+        cloudinit_iso = self.download_cloudinit(ssh_pubkey)
         self.vm.add_args('-drive', 'file=%s,format=raw' % cloudinit_iso)
 
     def launch_and_wait(self):
diff --git a/tests/acceptance/virtiofs_submounts.py b/tests/acceptance/virtiofs_submounts.py
new file mode 100644
index 0000000000..8b207b3e57
--- /dev/null
+++ b/tests/acceptance/virtiofs_submounts.py
@@ -0,0 +1,289 @@
+import logging
+import re
+import os
+import subprocess
+import time
+
+from avocado import skipUnless
+from avocado_qemu import Test, BUILD_DIR
+from avocado_qemu import wait_for_console_pattern
+from avocado.utils import ssh
+
+from qemu.accel import kvm_available
+
+from boot_linux import BootLinux
+
+
+def run_cmd(args):
+    subp = subprocess.Popen(args,
+                            stdout=subprocess.PIPE,
+                            stderr=subprocess.PIPE,
+                            universal_newlines=True)
+    stdout, stderr = subp.communicate()
+    ret = subp.returncode
+
+    return (stdout, stderr, ret)
+
+def has_passwordless_sudo():
+    """
+    This function is for use in a @avocado.skipUnless decorator, e.g.:
+
+        @skipUnless(*has_passwordless_sudo())
+        def test_something_that_needs_sudo(self):
+            ...
+    """
+
+    _, stderr, exitcode = run_cmd(('sudo', '-n', 'true'))
+    if exitcode != 0:
+        return (False, f'Failed to use sudo -n: {stderr.strip()}')
+    else:
+        return (True, '')
+
+
+class VirtiofsSubmountsTest(BootLinux):
+    """
+    :avocado: tags=arch:x86_64
+    """
+
+    def get_portfwd(self):
+        port = None
+
+        res = self.vm.command('human-monitor-command',
+                              command_line='info usernet')
+        for line in res.split('\r\n'):
+            match = \
+                re.search(r'TCP.HOST_FORWARD.*127\.0\.0\.1\s*(\d+)\s+10\.',
+                          line)
+            if match is not None:
+                port = match[1]
+                break
+
+        self.assertIsNotNone(port)
+        self.log.debug('sshd listening on port: ' + port)
+        return port
+
+    def ssh_connect(self, username, keyfile):
+        self.ssh_logger = logging.getLogger('ssh')
+        port = self.get_portfwd()
+        self.ssh_session = ssh.Session('127.0.0.1', port=int(port),
+                                       user=username, key=keyfile)
+        for i in range(10):
+            try:
+                self.ssh_session.connect()
+                return
+            except:
+                time.sleep(4)
+                pass
+        self.fail('sshd timeout')
+
+    def ssh_command(self, command):
+        self.ssh_logger.info(command)
+        result = self.ssh_session.cmd(command)
+        stdout_lines = [line.rstrip() for line
+                        in result.stdout_text.splitlines()]
+        for line in stdout_lines:
+            self.ssh_logger.info(line)
+        stderr_lines = [line.rstrip() for line
+                        in result.stderr_text.splitlines()]
+        for line in stderr_lines:
+            self.ssh_logger.warning(line)
+
+        self.assertEqual(result.exit_status, 0,
+                         f'Guest command failed: {command}')
+        return stdout_lines, stderr_lines
+
+    def run(self, args, ignore_error=False):
+        stdout, stderr, ret = run_cmd(args)
+
+        if ret != 0:
+            cmdline = ' '.join(args)
+            if not ignore_error:
+                self.fail(f'{cmdline}: Returned {ret}: {stderr}')
+            else:
+                self.log.warn(f'{cmdline}: Returned {ret}: {stderr}')
+
+        return (stdout, stderr, ret)
+
+    def set_up_shared_dir(self):
+        atwd = os.getenv('AVOCADO_TEST_WORKDIR')
+        self.shared_dir = os.path.join(atwd, 'virtiofs-shared')
+
+        os.mkdir(self.shared_dir)
+
+        self.run(('cp', self.get_data('guest.sh'),
+                 os.path.join(self.shared_dir, 'check.sh')))
+
+        self.run(('cp', self.get_data('guest-cleanup.sh'),
+                 os.path.join(self.shared_dir, 'cleanup.sh')))
+
+    def set_up_virtiofs(self):
+        attmp = os.getenv('AVOCADO_TESTS_COMMON_TMPDIR')
+        self.vfsdsock = os.path.join(attmp, 'vfsdsock')
+
+        self.run(('sudo', '-n', 'rm', '-f', self.vfsdsock), ignore_error=True)
+
+        self.virtiofsd = \
+            subprocess.Popen(('sudo', '-n',
+                              'tools/virtiofsd/virtiofsd',
+                              f'--socket-path={self.vfsdsock}',
+                              '-o', f'source={self.shared_dir}',
+                              '-o', 'cache=always',
+                              '-o', 'xattr',
+                              '-o', 'announce_submounts',
+                              '-f'),
+                             stdout=subprocess.DEVNULL,
+                             stderr=subprocess.PIPE,
+                             universal_newlines=True)
+
+        while not os.path.exists(self.vfsdsock):
+            if self.virtiofsd.poll() is not None:
+                self.fail('virtiofsd exited prematurely: ' +
+                          self.virtiofsd.communicate()[1])
+            time.sleep(0.1)
+
+        self.run(('sudo', '-n', 'chmod', 'go+rw', self.vfsdsock))
+
+        self.vm.add_args('-chardev',
+                         f'socket,id=vfsdsock,path={self.vfsdsock}',
+                         '-device',
+                         'vhost-user-fs-pci,queue-size=1024,chardev=vfsdsock' \
+                             ',tag=host',
+                         '-object',
+                         'memory-backend-file,id=mem,size=1G,' \
+                             'mem-path=/dev/shm,share=on',
+                         '-numa',
+                         'node,memdev=mem')
+
+    def launch_vm(self):
+        self.launch_and_wait()
+        self.ssh_connect('root', self.ssh_key)
+
+    def set_up_nested_mounts(self):
+        scratch_dir = os.path.join(self.shared_dir, 'scratch')
+        try:
+            os.mkdir(scratch_dir)
+        except FileExistsError:
+            pass
+
+        args = ['bash', self.get_data('host.sh'), scratch_dir]
+        if self.seed:
+            args += [self.seed]
+
+        out, _, _ = self.run(args)
+        seed = re.search(r'^Seed: \d+', out)
+        self.log.info(seed[0])
+
+    def mount_in_guest(self):
+        self.ssh_command('mkdir -p /mnt/host')
+        self.ssh_command('mount -t virtiofs host /mnt/host')
+
+    def check_in_guest(self):
+        self.ssh_command('bash /mnt/host/check.sh /mnt/host/scratch/share')
+
+    def live_cleanup(self):
+        self.ssh_command('bash /mnt/host/cleanup.sh /mnt/host/scratch')
+
+        # It would be nice if the above was sufficient to make virtiofsd clear
+        # all references to the mounted directories (so they can be unmounted
+        # on the host), but unfortunately it is not.  To do so, we have to
+        # resort to a remount.
+        self.ssh_command('mount -o remount /mnt/host')
+
+        scratch_dir = os.path.join(self.shared_dir, 'scratch')
+        self.run(('bash', self.get_data('cleanup.sh'), scratch_dir))
+
+    @skipUnless(*has_passwordless_sudo())
+    def setUp(self):
+        vmlinuz = self.params.get('vmlinuz')
+        if vmlinuz is None:
+            self.cancel('vmlinuz parameter not set; you must point it to a '
+                        'Linux kernel binary to test (to run this test with ' \
+                        'the on-image kernel, set it to an empty string)')
+
+        self.seed = self.params.get('seed')
+
+        atwd = os.getenv('AVOCADO_TEST_WORKDIR')
+        self.ssh_key = os.path.join(atwd, 'id_ed25519')
+
+        self.run(('ssh-keygen', '-t', 'ed25519', '-f', self.ssh_key))
+
+        pubkey = open(self.ssh_key + '.pub').read()
+
+        super(VirtiofsSubmountsTest, self).setUp(pubkey)
+
+        if len(vmlinuz) > 0:
+            self.vm.add_args('-kernel', vmlinuz,
+                             '-append', 'console=ttyS0 root=/dev/sda1')
+
+        # Allow us to connect to SSH
+        self.vm.add_args('-netdev', 'user,id=vnet,hostfwd=:127.0.0.1:0-:22',
+                         '-device', 'e1000,netdev=vnet')
+
+        if not kvm_available(self.arch, self.qemu_bin):
+            self.cancel(KVM_NOT_AVAILABLE)
+        self.vm.add_args('-accel', 'kvm')
+
+    def tearDown(self):
+        try:
+            self.vm.shutdown()
+        except:
+            pass
+
+        scratch_dir = os.path.join(self.shared_dir, 'scratch')
+        self.run(('bash', self.get_data('cleanup.sh'), scratch_dir),
+                 ignore_error=True)
+
+    def test_pre_virtiofsd_set_up(self):
+        self.set_up_shared_dir()
+
+        self.set_up_nested_mounts()
+
+        self.set_up_virtiofs()
+        self.launch_vm()
+        self.mount_in_guest()
+        self.check_in_guest()
+
+    def test_pre_launch_set_up(self):
+        self.set_up_shared_dir()
+        self.set_up_virtiofs()
+
+        self.set_up_nested_mounts()
+
+        self.launch_vm()
+        self.mount_in_guest()
+        self.check_in_guest()
+
+    def test_post_launch_set_up(self):
+        self.set_up_shared_dir()
+        self.set_up_virtiofs()
+        self.launch_vm()
+
+        self.set_up_nested_mounts()
+
+        self.mount_in_guest()
+        self.check_in_guest()
+
+    def test_post_mount_set_up(self):
+        self.set_up_shared_dir()
+        self.set_up_virtiofs()
+        self.launch_vm()
+        self.mount_in_guest()
+
+        self.set_up_nested_mounts()
+
+        self.check_in_guest()
+
+    def test_two_runs(self):
+        self.set_up_shared_dir()
+
+        self.set_up_nested_mounts()
+
+        self.set_up_virtiofs()
+        self.launch_vm()
+        self.mount_in_guest()
+        self.check_in_guest()
+
+        self.live_cleanup()
+        self.set_up_nested_mounts()
+
+        self.check_in_guest()
diff --git a/tests/acceptance/virtiofs_submounts.py.data/cleanup.sh b/tests/acceptance/virtiofs_submounts.py.data/cleanup.sh
new file mode 100644
index 0000000000..2a6579a0fe
--- /dev/null
+++ b/tests/acceptance/virtiofs_submounts.py.data/cleanup.sh
@@ -0,0 +1,46 @@
+#!/bin/bash
+
+function print_usage()
+{
+    if [ -n "$2" ]; then
+        echo "Error: $2"
+        echo
+    fi
+    echo "Usage: $1 <scratch dir>"
+}
+
+scratch_dir=$1
+if [ -z "$scratch_dir" ]; then
+    print_usage "$0" 'Scratch dir not given' >&2
+    exit 1
+fi
+
+cd "$scratch_dir/share" || exit 1
+mps=(mnt*)
+mp_i=0
+for mp in "${mps[@]}"; do
+    mp_i=$((mp_i + 1))
+    printf "Unmounting %i/%i...\r" "$mp_i" "${#mps[@]}"
+
+    sudo umount -R "$mp"
+    rm -rf "$mp"
+done
+echo
+
+rm some-file
+cd ..
+rmdir share
+
+imgs=(fs*.img)
+img_i=0
+for img in "${imgs[@]}"; do
+    img_i=$((img_i + 1))
+    printf "Detaching and deleting %i/%i...\r" "$img_i" "${#imgs[@]}"
+
+    dev=$(losetup -j "$img" | sed -e 's/:.*//')
+    sudo losetup -d "$dev"
+    rm -f "$img"
+done
+echo
+
+echo 'Done.'
diff --git a/tests/acceptance/virtiofs_submounts.py.data/guest-cleanup.sh b/tests/acceptance/virtiofs_submounts.py.data/guest-cleanup.sh
new file mode 100644
index 0000000000..729cb2d1a5
--- /dev/null
+++ b/tests/acceptance/virtiofs_submounts.py.data/guest-cleanup.sh
@@ -0,0 +1,30 @@
+#!/bin/bash
+
+function print_usage()
+{
+    if [ -n "$2" ]; then
+        echo "Error: $2"
+        echo
+    fi
+    echo "Usage: $1 <scratch dir>"
+}
+
+scratch_dir=$1
+if [ -z "$scratch_dir" ]; then
+    print_usage "$0" 'Scratch dir not given' >&2
+    exit 1
+fi
+
+cd "$scratch_dir/share" || exit 1
+
+mps=(mnt*)
+mp_i=0
+for mp in "${mps[@]}"; do
+    mp_i=$((mp_i + 1))
+    printf "Unmounting %i/%i...\r" "$mp_i" "${#mps[@]}"
+
+    sudo umount -R "$mp"
+done
+echo
+
+echo 'Done.'
diff --git a/tests/acceptance/virtiofs_submounts.py.data/guest.sh b/tests/acceptance/virtiofs_submounts.py.data/guest.sh
new file mode 100644
index 0000000000..59ba40fde1
--- /dev/null
+++ b/tests/acceptance/virtiofs_submounts.py.data/guest.sh
@@ -0,0 +1,138 @@
+#!/bin/bash
+
+function print_usage()
+{
+    if [ -n "$2" ]; then
+        echo "Error: $2"
+        echo
+    fi
+    echo "Usage: $1 <shared dir>"
+    echo '(The shared directory is the "share" directory in the scratch' \
+         'directory)'
+}
+
+shared_dir=$1
+if [ -z "$shared_dir" ]; then
+    print_usage "$0" 'Shared dir not given' >&2
+    exit 1
+fi
+
+cd "$shared_dir"
+
+# FIXME: This should not be necessary, but it is.  In order for all
+# submounts to be proper mount points, we need to visit them.
+# (Before we visit them, they will not be auto-mounted, and so just
+# appear as normal directories, with the catch that their st_ino will
+# be the st_ino of the filesystem they host, while the st_dev will
+# still be the st_dev of the parent.)
+# `find` does not work, because it will refuse to touch the mount
+# points as long as they are not mounted; their st_dev being shared
+# with the parent and st_ino just being the root node's inode ID
+# will practically ensure that this node exists elsewhere on the
+# filesystem, and `find` is required to recognize loops and not to
+# follow them.
+# Thus, we have to manually visit all nodes first.
+
+mnt_i=0
+
+function recursively_visit()
+{
+    pushd "$1" >/dev/null
+    for entry in *; do
+        if [[ "$entry" == mnt* ]]; then
+            mnt_i=$((mnt_i + 1))
+            printf "Triggering auto-mount $mnt_i...\r"
+        fi
+
+        if [ -d "$entry" ]; then
+            recursively_visit "$entry"
+        fi
+    done
+    popd >/dev/null
+}
+
+recursively_visit .
+echo
+
+
+if [ -n "$(find -name not-mounted)" ]; then
+    echo "Error: not-mounted files visible on mount points:" >&2
+    find -name not-mounted >&2
+    exit 1
+fi
+
+if [ ! -f some-file -o "$(cat some-file)" != 'root' ]; then
+    echo "Error: Bad file in the share root" >&2
+    exit 1
+fi
+
+shopt -s nullglob
+
+function check_submounts()
+{
+    local base_path=$1
+
+    for mp in mnt*; do
+        printf "Checking submount %i...\r" "$((${#devs[@]} + 1))"
+
+        mp_i=$(echo "$mp" | sed -e 's/mnt//')
+        dev=$(stat -c '%D' "$mp")
+
+        if [ -n "${devs[mp_i]}" ]; then
+            echo "Error: $mp encountered twice" >&2
+            exit 1
+        fi
+        devs[mp_i]=$dev
+
+        pushd "$mp" >/dev/null
+        path="$base_path$mp"
+        while true; do
+            expected_content="$(printf '%s\n%s\n' "$mp_i" "$path")"
+            if [ ! -f some-file ]; then
+                echo "Error: $PWD/some-file does not exist" >&2
+                exit 1
+            fi
+
+            if [ "$(cat some-file)" != "$expected_content" ]; then
+                echo "Error: Bad content in $PWD/some-file:" >&2
+                echo '--- found ---'
+                cat some-file
+                echo '--- expected ---'
+                echo "$expected_content"
+                exit 1
+            fi
+            if [ "$(stat -c '%D' some-file)" != "$dev" ]; then
+                echo "Error: $PWD/some-file has the wrong device ID" >&2
+                exit 1
+            fi
+
+            if [ -d sub ]; then
+                if [ "$(stat -c '%D' sub)" != "$dev" ]; then
+                    echo "Error: $PWD/some-file has the wrong device ID" >&2
+                    exit 1
+                fi
+                cd sub
+                path="$path/sub"
+            else
+                if [ -n "$(echo mnt*)" ]; then
+                    check_submounts "$path/"
+                fi
+                break
+            fi
+        done
+        popd >/dev/null
+    done
+}
+
+root_dev=$(stat -c '%D' some-file)
+devs=()
+check_submounts ''
+echo
+
+reused_devs=$(echo "$root_dev ${devs[@]}" | tr ' ' '\n' | sort | uniq -d)
+if [ -n "$reused_devs" ]; then
+    echo "Error: Reused device IDs: $reused_devs" >&2
+    exit 1
+fi
+
+echo "Test passed for ${#devs[@]} submounts."
diff --git a/tests/acceptance/virtiofs_submounts.py.data/host.sh b/tests/acceptance/virtiofs_submounts.py.data/host.sh
new file mode 100644
index 0000000000..d8a9afebdb
--- /dev/null
+++ b/tests/acceptance/virtiofs_submounts.py.data/host.sh
@@ -0,0 +1,127 @@
+#!/bin/bash
+
+mount_count=128
+
+function print_usage()
+{
+    if [ -n "$2" ]; then
+        echo "Error: $2"
+        echo
+    fi
+    echo "Usage: $1 <scratch dir> [seed]"
+    echo "(If no seed is given, it will be randomly generated.)"
+}
+
+scratch_dir=$1
+if [ -z "$scratch_dir" ]; then
+    print_usage "$0" 'No scratch dir given' >&2
+    exit 1
+fi
+
+if [ ! -d "$scratch_dir" ]; then
+    print_usage "$0" "$scratch_dir is not a directory" >&2
+    exit 1
+fi
+
+seed=$2
+if [ -z "$seed" ]; then
+    seed=$RANDOM
+fi
+RANDOM=$seed
+
+echo "Seed: $seed"
+
+set -e
+shopt -s nullglob
+
+cd "$scratch_dir"
+if [ -d share ]; then
+    echo 'Error: This directory seems to be in use already' >&2
+    exit 1
+fi
+
+for ((i = 0; i < $mount_count; i++)); do
+    printf "Setting up fs %i/%i...\r" "$((i + 1))" "$mount_count"
+
+    rm -f fs$i.img
+    truncate -s 512M fs$i.img
+    mkfs.xfs -q fs$i.img
+    devs[i]=$(sudo losetup -f --show fs$i.img)
+done
+echo
+
+top_level_mounts=$((RANDOM % mount_count + 1))
+
+mkdir -p share
+echo 'root' > share/some-file
+
+for ((i = 0; i < $top_level_mounts; i++)); do
+    printf "Mounting fs %i/%i...\r" "$((i + 1))" "$mount_count"
+
+    mkdir -p share/mnt$i
+    touch share/mnt$i/not-mounted
+    sudo mount "${devs[i]}" share/mnt$i
+    sudo chown "$(id -u):$(id -g)" share/mnt$i
+
+    pushd share/mnt$i >/dev/null
+    path=mnt$i
+    nesting=$((RANDOM % 4))
+    for ((j = 0; j < $nesting; j++)); do
+        cat > some-file <<EOF
+$i
+$path
+EOF
+        mkdir sub
+        cd sub
+        path="$path/sub"
+    done
+cat > some-file <<EOF
+$i
+$path
+EOF
+    popd >/dev/null
+done
+
+for ((; i < $mount_count; i++)); do
+    printf "Mounting fs %i/%i...\r" "$((i + 1))" "$mount_count"
+
+    mp_i=$((i % top_level_mounts))
+
+    pushd share/mnt$mp_i >/dev/null
+    path=mnt$mp_i
+    while true; do
+        sub_mp="$(echo mnt*)"
+        if cd sub 2>/dev/null; then
+            path="$path/sub"
+        elif [ -n "$sub_mp" ] && cd "$sub_mp" 2>/dev/null; then
+            path="$path/$sub_mp"
+        else
+            break
+        fi
+    done
+    mkdir mnt$i
+    touch mnt$i/not-mounted
+    sudo mount "${devs[i]}" mnt$i
+    sudo chown "$(id -u):$(id -g)" mnt$i
+
+    cd mnt$i
+    path="$path/mnt$i"
+    nesting=$((RANDOM % 4))
+    for ((j = 0; j < $nesting; j++)); do
+        cat > some-file <<EOF
+$i
+$path
+EOF
+        mkdir sub
+        cd sub
+        path="$path/sub"
+    done
+    cat > some-file <<EOF
+$i
+$path
+EOF
+    popd >/dev/null
+done
+echo
+
+echo 'Done.'
diff --git a/tools/meson.build b/tools/meson.build
index 513bd2ff4f..76bf84df52 100644
--- a/tools/meson.build
+++ b/tools/meson.build
@@ -1,10 +1,23 @@
-have_virtiofsd = (have_system and
+have_virtiofsd = (targetos == 'linux' and
     have_tools and
-    'CONFIG_LINUX' in config_host and 
     'CONFIG_SECCOMP' in config_host and
     'CONFIG_LIBCAP_NG' in config_host and
     'CONFIG_VHOST_USER' in config_host)
 
+if get_option('virtiofsd').enabled()
+  if not have_virtiofsd
+    if targetos != 'linux'
+      error('virtiofsd requires Linux')
+    elif 'CONFIG_SECCOMP' not in config_host or 'CONFIG_LIBCAP_NG' not in config_host
+      error('virtiofsd requires libcap-ng-devel and seccomp-devel')
+    elif not have_tools or 'CONFIG_VHOST_USER' not in config_host
+      error('virtiofsd needs tools and vhost-user support')
+    endif
+  endif
+elif get_option('virtiofsd').disabled() or not have_system
+  have_virtiofsd = false
+endif
+
 if have_virtiofsd
   subdir('virtiofsd')
 endif
diff --git a/tools/virtiofsd/fuse_common.h b/tools/virtiofsd/fuse_common.h
index 686c42c0a5..870544fe13 100644
--- a/tools/virtiofsd/fuse_common.h
+++ b/tools/virtiofsd/fuse_common.h
@@ -353,6 +353,14 @@ struct fuse_file_info {
 #define FUSE_CAP_NO_OPENDIR_SUPPORT (1 << 24)
 
 /**
+ * Indicates that the client will provide fuse_attr.flags, and the kernel will
+ * interpret it.
+ *
+ * This feature is enabled by default when supported by the kernel.
+ */
+#define FUSE_CAP_ATTR_FLAGS (1 << 27)
+
+/**
  * Ioctl flags
  *
  * FUSE_IOCTL_COMPAT: 32bit compat ioctl on 64bit machine
diff --git a/tools/virtiofsd/fuse_lowlevel.c b/tools/virtiofsd/fuse_lowlevel.c
index 4d1ba2925d..5198f627bc 100644
--- a/tools/virtiofsd/fuse_lowlevel.c
+++ b/tools/virtiofsd/fuse_lowlevel.c
@@ -329,7 +329,8 @@ static unsigned int calc_timeout_nsec(double t)
     }
 }
 
-static void fill_entry(struct fuse_entry_out *arg,
+static void fill_entry(struct fuse_session *se,
+                       struct fuse_entry_out *arg,
                        const struct fuse_entry_param *e)
 {
     *arg = (struct fuse_entry_out){
@@ -341,6 +342,10 @@ static void fill_entry(struct fuse_entry_out *arg,
         .attr_valid_nsec = calc_timeout_nsec(e->attr_timeout),
     };
     convert_stat(&e->attr, &arg->attr);
+
+    if (se->conn.capable & FUSE_CAP_ATTR_FLAGS) {
+        arg->attr.flags = e->attr_flags;
+    }
 }
 
 /*
@@ -365,7 +370,7 @@ size_t fuse_add_direntry_plus(fuse_req_t req, char *buf, size_t bufsize,
 
     struct fuse_direntplus *dp = (struct fuse_direntplus *)buf;
     memset(&dp->entry_out, 0, sizeof(dp->entry_out));
-    fill_entry(&dp->entry_out, e);
+    fill_entry(req->se, &dp->entry_out, e);
 
     struct fuse_dirent *dirent = &dp->dirent;
     *dirent = (struct fuse_dirent){
@@ -403,7 +408,7 @@ int fuse_reply_entry(fuse_req_t req, const struct fuse_entry_param *e)
     size_t size = sizeof(arg);
 
     memset(&arg, 0, sizeof(arg));
-    fill_entry(&arg, e);
+    fill_entry(req->se, &arg, e);
     return send_reply_ok(req, &arg, size);
 }
 
@@ -416,13 +421,13 @@ int fuse_reply_create(fuse_req_t req, const struct fuse_entry_param *e,
     struct fuse_open_out *oarg = (struct fuse_open_out *)(buf + entrysize);
 
     memset(buf, 0, sizeof(buf));
-    fill_entry(earg, e);
+    fill_entry(req->se, earg, e);
     fill_open(oarg, f);
     return send_reply_ok(req, buf, entrysize + sizeof(struct fuse_open_out));
 }
 
-int fuse_reply_attr(fuse_req_t req, const struct stat *attr,
-                    double attr_timeout)
+int fuse_reply_attr_with_flags(fuse_req_t req, const struct stat *attr,
+                               double attr_timeout, uint32_t attr_flags)
 {
     struct fuse_attr_out arg;
     size_t size = sizeof(arg);
@@ -432,9 +437,19 @@ int fuse_reply_attr(fuse_req_t req, const struct stat *attr,
     arg.attr_valid_nsec = calc_timeout_nsec(attr_timeout);
     convert_stat(attr, &arg.attr);
 
+    if (req->se->conn.capable & FUSE_CAP_ATTR_FLAGS) {
+        arg.attr.flags = attr_flags;
+    }
+
     return send_reply_ok(req, &arg, size);
 }
 
+int fuse_reply_attr(fuse_req_t req, const struct stat *attr,
+                    double attr_timeout)
+{
+    return fuse_reply_attr_with_flags(req, attr, attr_timeout, 0);
+}
+
 int fuse_reply_readlink(fuse_req_t req, const char *linkname)
 {
     return send_reply_ok(req, linkname, strlen(linkname));
@@ -1988,6 +2003,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
             bufsize = max_bufsize;
         }
     }
+    if (arg->flags & FUSE_ATTR_FLAGS) {
+        se->conn.capable |= FUSE_CAP_ATTR_FLAGS;
+    }
 #ifdef HAVE_SPLICE
 #ifdef HAVE_VMSPLICE
     se->conn.capable |= FUSE_CAP_SPLICE_WRITE | FUSE_CAP_SPLICE_MOVE;
@@ -2014,6 +2032,7 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
     LL_SET_DEFAULT(1, FUSE_CAP_ASYNC_DIO);
     LL_SET_DEFAULT(1, FUSE_CAP_IOCTL_DIR);
     LL_SET_DEFAULT(1, FUSE_CAP_ATOMIC_O_TRUNC);
+    LL_SET_DEFAULT(1, FUSE_CAP_ATTR_FLAGS);
     LL_SET_DEFAULT(se->op.write_buf, FUSE_CAP_SPLICE_READ);
     LL_SET_DEFAULT(se->op.getlk && se->op.setlk, FUSE_CAP_POSIX_LOCKS);
     LL_SET_DEFAULT(se->op.flock, FUSE_CAP_FLOCK_LOCKS);
@@ -2103,6 +2122,9 @@ static void do_init(fuse_req_t req, fuse_ino_t nodeid,
     if (se->conn.want & FUSE_CAP_POSIX_ACL) {
         outarg.flags |= FUSE_POSIX_ACL;
     }
+    if (se->conn.want & FUSE_CAP_ATTR_FLAGS) {
+        outarg.flags |= FUSE_ATTR_FLAGS;
+    }
     outarg.max_readahead = se->conn.max_readahead;
     outarg.max_write = se->conn.max_write;
     if (se->conn.max_background >= (1 << 16)) {
diff --git a/tools/virtiofsd/fuse_lowlevel.h b/tools/virtiofsd/fuse_lowlevel.h
index 562fd5241e..1ff6ba1e4f 100644
--- a/tools/virtiofsd/fuse_lowlevel.h
+++ b/tools/virtiofsd/fuse_lowlevel.h
@@ -102,6 +102,11 @@ struct fuse_entry_param {
      *  large value.
      */
     double entry_timeout;
+
+    /**
+     * Flags for fuse_attr.flags that do not fit into attr.
+     */
+    uint32_t attr_flags;
 };
 
 /**
@@ -1309,6 +1314,21 @@ int fuse_reply_attr(fuse_req_t req, const struct stat *attr,
                     double attr_timeout);
 
 /**
+ * Reply with attributes and set fuse_attr.flags
+ *
+ * Possible requests:
+ *   getattr, setattr
+ *
+ * @param req request handle
+ * @param attr the attributes
+ * @param attr_timeout validity timeout (in seconds) for the attributes
+ * @param attr_flags flags to put into fuse_attr.flags
+ * @return zero for success, -errno for failure to send reply
+ */
+int fuse_reply_attr_with_flags(fuse_req_t req, const struct stat *attr,
+                               double attr_timeout, uint32_t attr_flags);
+
+/**
  * Reply with the contents of a symbolic link
  *
  * Possible requests:
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c
index 85770d63f1..a212f32931 100644
--- a/tools/virtiofsd/helper.c
+++ b/tools/virtiofsd/helper.c
@@ -166,10 +166,19 @@ void fuse_cmdline_help(void)
            "                               enable/disable readirplus\n"
            "                               default: readdirplus except with "
            "cache=none\n"
+           "    -o sandbox=namespace|chroot\n"
+           "                               sandboxing mode:\n"
+           "                               - namespace: mount, pid, and net\n"
+           "                                 namespaces with pivot_root(2)\n"
+           "                                 into shared directory\n"
+           "                               - chroot: chroot(2) into shared\n"
+           "                                 directory (use in containers)\n"
+           "                               default: namespace\n"
            "    -o timeout=<number>        I/O timeout (seconds)\n"
            "                               default: depends on cache= option.\n"
            "    -o writeback|no_writeback  enable/disable writeback cache\n"
            "                               default: no_writeback\n"
+           "    -o announce_submounts      Announce sub-mount points to the guest\n"
            "    -o xattr|no_xattr          enable/disable xattr\n"
            "                               default: no_xattr\n"
            "    -o modcaps=CAPLIST         Modify the list of capabilities\n"
diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index ff53df4451..4db50046d4 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -40,6 +40,7 @@
 #include "fuse_virtio.h"
 #include "fuse_log.h"
 #include "fuse_lowlevel.h"
+#include "standard-headers/linux/fuse.h"
 #include <assert.h>
 #include <cap-ng.h>
 #include <dirent.h>
@@ -64,6 +65,7 @@
 #include <syslog.h>
 #include <unistd.h>
 
+#include "qemu/cutils.h"
 #include "passthrough_helpers.h"
 #include "passthrough_seccomp.h"
 
@@ -124,6 +126,14 @@ struct lo_inode {
     GHashTable *posix_locks; /* protected by lo_inode->plock_mutex */
 
     mode_t filetype;
+
+    /*
+     * So we can detect crossmount roots
+     * (As such, this only needs to be valid for directories.  Note
+     * that files can have multiple parents due to hard links, and so
+     * their parent_dev may fluctuate.)
+     */
+    dev_t parent_dev;
 };
 
 struct lo_cred {
@@ -137,13 +147,26 @@ enum {
     CACHE_ALWAYS,
 };
 
+enum {
+    SANDBOX_NAMESPACE,
+    SANDBOX_CHROOT,
+};
+
+typedef struct xattr_map_entry {
+    char *key;
+    char *prepend;
+    unsigned int flags;
+} XattrMapEntry;
+
 struct lo_data {
     pthread_mutex_t mutex;
+    int sandbox;
     int debug;
     int writeback;
     int flock;
     int posix_lock;
     int xattr;
+    char *xattrmap;
     char *source;
     char *modcaps;
     double timeout;
@@ -151,18 +174,27 @@ struct lo_data {
     int timeout_set;
     int readdirplus_set;
     int readdirplus_clear;
+    int announce_submounts;
     int allow_direct_io;
     struct lo_inode root;
     GHashTable *inodes; /* protected by lo->mutex */
     struct lo_map ino_map; /* protected by lo->mutex */
     struct lo_map dirp_map; /* protected by lo->mutex */
     struct lo_map fd_map; /* protected by lo->mutex */
+    XattrMapEntry *xattr_map_list;
+    size_t xattr_map_nentries;
 
     /* An O_PATH file descriptor to /proc/self/fd/ */
     int proc_self_fd;
 };
 
 static const struct fuse_opt lo_opts[] = {
+    { "sandbox=namespace",
+      offsetof(struct lo_data, sandbox),
+      SANDBOX_NAMESPACE },
+    { "sandbox=chroot",
+      offsetof(struct lo_data, sandbox),
+      SANDBOX_CHROOT },
     { "writeback", offsetof(struct lo_data, writeback), 1 },
     { "no_writeback", offsetof(struct lo_data, writeback), 0 },
     { "source=%s", offsetof(struct lo_data, source), 0 },
@@ -172,6 +204,7 @@ static const struct fuse_opt lo_opts[] = {
     { "no_posix_lock", offsetof(struct lo_data, posix_lock), 0 },
     { "xattr", offsetof(struct lo_data, xattr), 1 },
     { "no_xattr", offsetof(struct lo_data, xattr), 0 },
+    { "xattrmap=%s", offsetof(struct lo_data, xattrmap), 0 },
     { "modcaps=%s", offsetof(struct lo_data, modcaps), 0 },
     { "timeout=%lf", offsetof(struct lo_data, timeout), 0 },
     { "timeout=", offsetof(struct lo_data, timeout_set), 1 },
@@ -180,6 +213,7 @@ static const struct fuse_opt lo_opts[] = {
     { "cache=always", offsetof(struct lo_data, cache), CACHE_ALWAYS },
     { "readdirplus", offsetof(struct lo_data, readdirplus_set), 1 },
     { "no_readdirplus", offsetof(struct lo_data, readdirplus_clear), 1 },
+    { "announce_submounts", offsetof(struct lo_data, announce_submounts), 1 },
     { "allow_direct_io", offsetof(struct lo_data, allow_direct_io), 1 },
     { "no_allow_direct_io", offsetof(struct lo_data, allow_direct_io), 0 },
     FUSE_OPT_END
@@ -577,22 +611,52 @@ static void lo_init(void *userdata, struct fuse_conn_info *conn)
     }
 }
 
+/**
+ * Call fstatat() and set st_rdev whenever a directory's st_dev
+ * differs from the rparent's st_dev (@parent_dev).  This will
+ * announce submounts to the FUSE client (unless @announce_submounts
+ * is false).
+ */
+static int do_fstatat(int dirfd, const char *pathname, struct stat *statbuf,
+                      int flags, dev_t parent_dev, uint32_t *fuse_attr_flags)
+{
+    int res = fstatat(dirfd, pathname, statbuf, flags);
+    if (res == -1) {
+        return res;
+    }
+
+    if (statbuf->st_dev != parent_dev && S_ISDIR(statbuf->st_mode) &&
+        fuse_attr_flags)
+    {
+        *fuse_attr_flags |= FUSE_ATTR_SUBMOUNT;
+    }
+
+    return 0;
+}
+
 static void lo_getattr(fuse_req_t req, fuse_ino_t ino,
                        struct fuse_file_info *fi)
 {
     int res;
     struct stat buf;
     struct lo_data *lo = lo_data(req);
+    struct lo_inode *inode = lo_inode(req, ino);
+    uint32_t fuse_attr_flags = 0;
 
     (void)fi;
 
-    res =
-        fstatat(lo_fd(req, ino), "", &buf, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+    res = do_fstatat(inode->fd, "", &buf, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
+                     inode->parent_dev, &fuse_attr_flags);
+    lo_inode_put(lo, &inode);
     if (res == -1) {
         return (void)fuse_reply_err(req, errno);
     }
 
-    fuse_reply_attr(req, &buf, lo->timeout);
+    if (!lo->announce_submounts) {
+        fuse_attr_flags &= ~FUSE_ATTR_SUBMOUNT;
+    }
+
+    fuse_reply_attr_with_flags(req, &buf, lo->timeout, fuse_attr_flags);
 }
 
 static int lo_fi_fd(fuse_req_t req, struct fuse_file_info *fi)
@@ -788,11 +852,16 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
         goto out_err;
     }
 
-    res = fstatat(newfd, "", &e->attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+    res = do_fstatat(newfd, "", &e->attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
+                     dir->key.dev, &e->attr_flags);
     if (res == -1) {
         goto out_err;
     }
 
+    if (!lo->announce_submounts) {
+        e->attr_flags &= ~FUSE_ATTR_SUBMOUNT;
+    }
+
     inode = lo_find(lo, &e->attr);
     if (inode) {
         close(newfd);
@@ -824,6 +893,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
         g_hash_table_insert(lo->inodes, &inode->key, inode);
         pthread_mutex_unlock(&lo->mutex);
     }
+    inode->parent_dev = dir->key.dev;
     e->ino = inode->fuse_ino;
     lo_inode_put(lo, &inode);
     lo_inode_put(lo, &dir);
@@ -1037,11 +1107,17 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
         goto out_err;
     }
 
-    res = fstatat(inode->fd, "", &e.attr, AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+    res = do_fstatat(inode->fd, "", &e.attr,
+                     AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW,
+                     parent_inode->key.dev, &e.attr_flags);
     if (res == -1) {
         goto out_err;
     }
 
+    if (!lo->announce_submounts) {
+        e.attr_flags &= ~FUSE_ATTR_SUBMOUNT;
+    }
+
     pthread_mutex_lock(&lo->mutex);
     inode->nlookup++;
     pthread_mutex_unlock(&lo->mutex);
@@ -1050,6 +1126,14 @@ static void lo_link(fuse_req_t req, fuse_ino_t ino, fuse_ino_t parent,
     fuse_log(FUSE_LOG_DEBUG, "  %lli/%s -> %lli\n", (unsigned long long)parent,
              name, (unsigned long long)e.ino);
 
+    /*
+     * No need to update inode->parent_dev, because
+     * (1) We cannot, the inode now has more than one parent,
+     * (2) Directories cannot have more than one parent, so link()
+     *     does not work for them; but parent_dev only needs to be
+     *     valid for directories.
+     */
+
     fuse_reply_entry(req, &e);
     lo_inode_put(lo, &parent_inode);
     lo_inode_put(lo, &inode);
@@ -1068,14 +1152,21 @@ static struct lo_inode *lookup_name(fuse_req_t req, fuse_ino_t parent,
 {
     int res;
     struct stat attr;
+    struct lo_data *lo = lo_data(req);
+    struct lo_inode *dir = lo_inode(req, parent);
 
-    res = fstatat(lo_fd(req, parent), name, &attr,
-                  AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW);
+    if (!dir) {
+        return NULL;
+    }
+
+    res = do_fstatat(dir->fd, name, &attr,
+                     AT_EMPTY_PATH | AT_SYMLINK_NOFOLLOW, dir->key.dev, NULL);
+    lo_inode_put(lo, &dir);
     if (res == -1) {
         return NULL;
     }
 
-    return lo_find(lo_data(req), &attr);
+    return lo_find(lo, &attr);
 }
 
 static void lo_rmdir(fuse_req_t req, fuse_ino_t parent, const char *name)
@@ -2010,20 +2101,383 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,
     fuse_reply_err(req, res == -1 ? errno : 0);
 }
 
-static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,
+/* types */
+/*
+ * Exit; process attribute unmodified if matched.
+ * An empty key applies to all.
+ */
+#define XATTR_MAP_FLAG_OK      (1 <<  0)
+/*
+ * The attribute is unwanted;
+ * EPERM on write, hidden on read.
+ */
+#define XATTR_MAP_FLAG_BAD     (1 <<  1)
+/*
+ * For attr that start with 'key' prepend 'prepend'
+ * 'key' may be empty to prepend for all attrs
+ * key is defined from set/remove point of view.
+ * Automatically reversed on read
+ */
+#define XATTR_MAP_FLAG_PREFIX  (1 <<  2)
+
+/* scopes */
+/* Apply rule to get/set/remove */
+#define XATTR_MAP_FLAG_CLIENT  (1 << 16)
+/* Apply rule to list */
+#define XATTR_MAP_FLAG_SERVER  (1 << 17)
+/* Apply rule to all */
+#define XATTR_MAP_FLAG_ALL   (XATTR_MAP_FLAG_SERVER | XATTR_MAP_FLAG_CLIENT)
+
+static void add_xattrmap_entry(struct lo_data *lo,
+                               const XattrMapEntry *new_entry)
+{
+    XattrMapEntry *res = g_realloc_n(lo->xattr_map_list,
+                                     lo->xattr_map_nentries + 1,
+                                     sizeof(XattrMapEntry));
+    res[lo->xattr_map_nentries++] = *new_entry;
+
+    lo->xattr_map_list = res;
+}
+
+static void free_xattrmap(struct lo_data *lo)
+{
+    XattrMapEntry *map = lo->xattr_map_list;
+    size_t i;
+
+    if (!map) {
+        return;
+    }
+
+    for (i = 0; i < lo->xattr_map_nentries; i++) {
+        g_free(map[i].key);
+        g_free(map[i].prepend);
+    };
+
+    g_free(map);
+    lo->xattr_map_list = NULL;
+    lo->xattr_map_nentries = -1;
+}
+
+/*
+ * Handle the 'map' type, which is sugar for a set of commands
+ * for the common case of prefixing a subset or everything,
+ * and allowing anything not prefixed through.
+ * It must be the last entry in the stream, although there
+ * can be other entries before it.
+ * The form is:
+ *    :map:key:prefix:
+ *
+ * key maybe empty in which case all entries are prefixed.
+ */
+static void parse_xattrmap_map(struct lo_data *lo,
+                               const char *rule, char sep)
+{
+    const char *tmp;
+    char *key;
+    char *prefix;
+    XattrMapEntry tmp_entry;
+
+    if (*rule != sep) {
+        fuse_log(FUSE_LOG_ERR,
+                 "%s: Expecting '%c' after 'map' keyword, found '%c'\n",
+                 __func__, sep, *rule);
+        exit(1);
+    }
+
+    rule++;
+
+    /* At start of 'key' field */
+    tmp = strchr(rule, sep);
+    if (!tmp) {
+        fuse_log(FUSE_LOG_ERR,
+                 "%s: Missing '%c' at end of key field in map rule\n",
+                 __func__, sep);
+        exit(1);
+    }
+
+    key = g_strndup(rule, tmp - rule);
+    rule = tmp + 1;
+
+    /* At start of prefix field */
+    tmp = strchr(rule, sep);
+    if (!tmp) {
+        fuse_log(FUSE_LOG_ERR,
+                 "%s: Missing '%c' at end of prefix field in map rule\n",
+                 __func__, sep);
+        exit(1);
+    }
+
+    prefix = g_strndup(rule, tmp - rule);
+    rule = tmp + 1;
+
+    /*
+     * This should be the end of the string, we don't allow
+     * any more commands after 'map'.
+     */
+    if (*rule) {
+        fuse_log(FUSE_LOG_ERR,
+                 "%s: Expecting end of command after map, found '%c'\n",
+                 __func__, *rule);
+        exit(1);
+    }
+
+    /* 1st: Prefix matches/everything */
+    tmp_entry.flags = XATTR_MAP_FLAG_PREFIX | XATTR_MAP_FLAG_ALL;
+    tmp_entry.key = g_strdup(key);
+    tmp_entry.prepend = g_strdup(prefix);
+    add_xattrmap_entry(lo, &tmp_entry);
+
+    if (!*key) {
+        /* Prefix all case */
+
+        /* 2nd: Hide any non-prefixed entries on the host */
+        tmp_entry.flags = XATTR_MAP_FLAG_BAD | XATTR_MAP_FLAG_ALL;
+        tmp_entry.key = g_strdup("");
+        tmp_entry.prepend = g_strdup("");
+        add_xattrmap_entry(lo, &tmp_entry);
+    } else {
+        /* Prefix matching case */
+
+        /* 2nd: Hide non-prefixed but matching entries on the host */
+        tmp_entry.flags = XATTR_MAP_FLAG_BAD | XATTR_MAP_FLAG_SERVER;
+        tmp_entry.key = g_strdup(""); /* Not used */
+        tmp_entry.prepend = g_strdup(key);
+        add_xattrmap_entry(lo, &tmp_entry);
+
+        /* 3rd: Stop the client accessing prefixed attributes directly */
+        tmp_entry.flags = XATTR_MAP_FLAG_BAD | XATTR_MAP_FLAG_CLIENT;
+        tmp_entry.key = g_strdup(prefix);
+        tmp_entry.prepend = g_strdup(""); /* Not used */
+        add_xattrmap_entry(lo, &tmp_entry);
+
+        /* 4th: Everything else is OK */
+        tmp_entry.flags = XATTR_MAP_FLAG_OK | XATTR_MAP_FLAG_ALL;
+        tmp_entry.key = g_strdup("");
+        tmp_entry.prepend = g_strdup("");
+        add_xattrmap_entry(lo, &tmp_entry);
+    }
+
+    g_free(key);
+    g_free(prefix);
+}
+
+static void parse_xattrmap(struct lo_data *lo)
+{
+    const char *map = lo->xattrmap;
+    const char *tmp;
+
+    lo->xattr_map_nentries = 0;
+    while (*map) {
+        XattrMapEntry tmp_entry;
+        char sep;
+
+        if (isspace(*map)) {
+            map++;
+            continue;
+        }
+        /* The separator is the first non-space of the rule */
+        sep = *map++;
+        if (!sep) {
+            break;
+        }
+
+        tmp_entry.flags = 0;
+        /* Start of 'type' */
+        if (strstart(map, "prefix", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_PREFIX;
+        } else if (strstart(map, "ok", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_OK;
+        } else if (strstart(map, "bad", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_BAD;
+        } else if (strstart(map, "map", &map)) {
+            /*
+             * map is sugar that adds a number of rules, and must be
+             * the last entry.
+             */
+            parse_xattrmap_map(lo, map, sep);
+            return;
+        } else {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Unexpected type;"
+                     "Expecting 'prefix', 'ok', 'bad' or 'map' in rule %zu\n",
+                     __func__, lo->xattr_map_nentries);
+            exit(1);
+        }
+
+        if (*map++ != sep) {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Missing '%c' at end of type field of rule %zu\n",
+                     __func__, sep, lo->xattr_map_nentries);
+            exit(1);
+        }
+
+        /* Start of 'scope' */
+        if (strstart(map, "client", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_CLIENT;
+        } else if (strstart(map, "server", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_SERVER;
+        } else if (strstart(map, "all", &map)) {
+            tmp_entry.flags |= XATTR_MAP_FLAG_ALL;
+        } else {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Unexpected scope;"
+                     " Expecting 'client', 'server', or 'all', in rule %zu\n",
+                     __func__, lo->xattr_map_nentries);
+            exit(1);
+        }
+
+        if (*map++ != sep) {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Expecting '%c' found '%c'"
+                     " after scope in rule %zu\n",
+                     __func__, sep, *map, lo->xattr_map_nentries);
+            exit(1);
+        }
+
+        /* At start of 'key' field */
+        tmp = strchr(map, sep);
+        if (!tmp) {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Missing '%c' at end of key field of rule %zu",
+                     __func__, sep, lo->xattr_map_nentries);
+            exit(1);
+        }
+        tmp_entry.key = g_strndup(map, tmp - map);
+        map = tmp + 1;
+
+        /* At start of 'prepend' field */
+        tmp = strchr(map, sep);
+        if (!tmp) {
+            fuse_log(FUSE_LOG_ERR,
+                     "%s: Missing '%c' at end of prepend field of rule %zu",
+                     __func__, sep, lo->xattr_map_nentries);
+            exit(1);
+        }
+        tmp_entry.prepend = g_strndup(map, tmp - map);
+        map = tmp + 1;
+
+        add_xattrmap_entry(lo, &tmp_entry);
+        /* End of rule - go around again for another rule */
+    }
+
+    if (!lo->xattr_map_nentries) {
+        fuse_log(FUSE_LOG_ERR, "Empty xattr map\n");
+        exit(1);
+    }
+}
+
+/*
+ * For use with getxattr/setxattr/removexattr, where the client
+ * gives us a name and we may need to choose a different one.
+ * Allocates a buffer for the result placing it in *out_name.
+ *   If there's no change then *out_name is not set.
+ * Returns 0 on success
+ * Can return -EPERM to indicate we block a given attribute
+ *   (in which case out_name is not allocated)
+ * Can return -ENOMEM to indicate out_name couldn't be allocated.
+ */
+static int xattr_map_client(const struct lo_data *lo, const char *client_name,
+                            char **out_name)
+{
+    size_t i;
+    for (i = 0; i < lo->xattr_map_nentries; i++) {
+        const XattrMapEntry *cur_entry = lo->xattr_map_list + i;
+
+        if ((cur_entry->flags & XATTR_MAP_FLAG_CLIENT) &&
+            (strstart(client_name, cur_entry->key, NULL))) {
+            if (cur_entry->flags & XATTR_MAP_FLAG_BAD) {
+                return -EPERM;
+            }
+            if (cur_entry->flags & XATTR_MAP_FLAG_OK) {
+                /* Unmodified name */
+                return 0;
+            }
+            if (cur_entry->flags & XATTR_MAP_FLAG_PREFIX) {
+                *out_name = g_try_malloc(strlen(client_name) +
+                                         strlen(cur_entry->prepend) + 1);
+                if (!*out_name) {
+                    return -ENOMEM;
+                }
+                sprintf(*out_name, "%s%s", cur_entry->prepend, client_name);
+                return 0;
+            }
+        }
+    }
+
+    return -EPERM;
+}
+
+/*
+ * For use with listxattr where the server fs gives us a name and we may need
+ * to sanitize this for the client.
+ * Returns a pointer to the result in *out_name
+ *   This is always the original string or the current string with some prefix
+ *   removed; no reallocation is done.
+ * Returns 0 on success
+ * Can return -ENODATA to indicate the name should be dropped from the list.
+ */
+static int xattr_map_server(const struct lo_data *lo, const char *server_name,
+                            const char **out_name)
+{
+    size_t i;
+    const char *end;
+
+    for (i = 0; i < lo->xattr_map_nentries; i++) {
+        const XattrMapEntry *cur_entry = lo->xattr_map_list + i;
+
+        if ((cur_entry->flags & XATTR_MAP_FLAG_SERVER) &&
+            (strstart(server_name, cur_entry->prepend, &end))) {
+            if (cur_entry->flags & XATTR_MAP_FLAG_BAD) {
+                return -ENODATA;
+            }
+            if (cur_entry->flags & XATTR_MAP_FLAG_OK) {
+                *out_name = server_name;
+                return 0;
+            }
+            if (cur_entry->flags & XATTR_MAP_FLAG_PREFIX) {
+                /* Remove prefix */
+                *out_name = end;
+                return 0;
+            }
+        }
+    }
+
+    return -ENODATA;
+}
+
+static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
                         size_t size)
 {
     struct lo_data *lo = lo_data(req);
     char *value = NULL;
     char procname[64];
+    const char *name;
+    char *mapped_name;
     struct lo_inode *inode;
     ssize_t ret;
     int saverr;
     int fd = -1;
 
+    mapped_name = NULL;
+    name = in_name;
+    if (lo->xattrmap) {
+        ret = xattr_map_client(lo, in_name, &mapped_name);
+        if (ret < 0) {
+            if (ret == -EPERM) {
+                ret = -ENODATA;
+            }
+            fuse_reply_err(req, -ret);
+            return;
+        }
+        if (mapped_name) {
+            name = mapped_name;
+        }
+    }
+
     inode = lo_inode(req, ino);
     if (!inode) {
         fuse_reply_err(req, EBADF);
+        g_free(mapped_name);
         return;
     }
 
@@ -2088,6 +2542,7 @@ out_err:
     saverr = errno;
 out:
     fuse_reply_err(req, saverr);
+    g_free(mapped_name);
     goto out_free;
 }
 
@@ -2144,8 +2599,60 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)
         if (ret == 0) {
             goto out;
         }
+
+        if (lo->xattr_map_list) {
+            /*
+             * Map the names back, some attributes might be dropped,
+             * some shortened, but not increased, so we shouldn't
+             * run out of room.
+             */
+            size_t out_index, in_index;
+            out_index = 0;
+            in_index = 0;
+            while (in_index < ret) {
+                const char *map_out;
+                char *in_ptr = value + in_index;
+                /* Length of current attribute name */
+                size_t in_len = strlen(value + in_index) + 1;
+
+                int mapret = xattr_map_server(lo, in_ptr, &map_out);
+                if (mapret != -ENODATA && mapret != 0) {
+                    /* Shouldn't happen */
+                    saverr = -mapret;
+                    goto out;
+                }
+                if (mapret == 0) {
+                    /* Either unchanged, or truncated */
+                    size_t out_len;
+                    if (map_out != in_ptr) {
+                        /* +1 copies the NIL */
+                        out_len = strlen(map_out) + 1;
+                    } else {
+                        /* No change */
+                        out_len = in_len;
+                    }
+                    /*
+                     * Move result along, may still be needed for an unchanged
+                     * entry if a previous entry was changed.
+                     */
+                    memmove(value + out_index, map_out, out_len);
+
+                    out_index += out_len;
+                }
+                in_index += in_len;
+            }
+            ret = out_index;
+            if (ret == 0) {
+                goto out;
+            }
+        }
         fuse_reply_buf(req, value, ret);
     } else {
+        /*
+         * xattrmap only ever shortens the result,
+         * so we don't need to do anything clever with the
+         * allocation length here.
+         */
         fuse_reply_xattr(req, ret);
     }
 out_free:
@@ -2165,19 +2672,35 @@ out:
     goto out_free;
 }
 
-static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *name,
+static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *in_name,
                         const char *value, size_t size, int flags)
 {
     char procname[64];
+    const char *name;
+    char *mapped_name;
     struct lo_data *lo = lo_data(req);
     struct lo_inode *inode;
     ssize_t ret;
     int saverr;
     int fd = -1;
 
+    mapped_name = NULL;
+    name = in_name;
+    if (lo->xattrmap) {
+        ret = xattr_map_client(lo, in_name, &mapped_name);
+        if (ret < 0) {
+            fuse_reply_err(req, -ret);
+            return;
+        }
+        if (mapped_name) {
+            name = mapped_name;
+        }
+    }
+
     inode = lo_inode(req, ino);
     if (!inode) {
         fuse_reply_err(req, EBADF);
+        g_free(mapped_name);
         return;
     }
 
@@ -2212,21 +2735,38 @@ out:
     }
 
     lo_inode_put(lo, &inode);
+    g_free(mapped_name);
     fuse_reply_err(req, saverr);
 }
 
-static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *name)
+static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *in_name)
 {
     char procname[64];
+    const char *name;
+    char *mapped_name;
     struct lo_data *lo = lo_data(req);
     struct lo_inode *inode;
     ssize_t ret;
     int saverr;
     int fd = -1;
 
+    mapped_name = NULL;
+    name = in_name;
+    if (lo->xattrmap) {
+        ret = xattr_map_client(lo, in_name, &mapped_name);
+        if (ret < 0) {
+            fuse_reply_err(req, -ret);
+            return;
+        }
+        if (mapped_name) {
+            name = mapped_name;
+        }
+    }
+
     inode = lo_inode(req, ino);
     if (!inode) {
         fuse_reply_err(req, EBADF);
+        g_free(mapped_name);
         return;
     }
 
@@ -2261,6 +2801,7 @@ out:
     }
 
     lo_inode_put(lo, &inode);
+    g_free(mapped_name);
     fuse_reply_err(req, saverr);
 }
 
@@ -2661,14 +3202,54 @@ static void setup_capabilities(char *modcaps_in)
 }
 
 /*
+ * Use chroot as a weaker sandbox for environments where the process is
+ * launched without CAP_SYS_ADMIN.
+ */
+static void setup_chroot(struct lo_data *lo)
+{
+    lo->proc_self_fd = open("/proc/self/fd", O_PATH);
+    if (lo->proc_self_fd == -1) {
+        fuse_log(FUSE_LOG_ERR, "open(\"/proc/self/fd\", O_PATH): %m\n");
+        exit(1);
+    }
+
+    /*
+     * Make the shared directory the file system root so that FUSE_OPEN
+     * (lo_open()) cannot escape the shared directory by opening a symlink.
+     *
+     * The chroot(2) syscall is later disabled by seccomp and the
+     * CAP_SYS_CHROOT capability is dropped so that tampering with the chroot
+     * is not possible.
+     *
+     * However, it's still possible to escape the chroot via lo->proc_self_fd
+     * but that requires first gaining control of the process.
+     */
+    if (chroot(lo->source) != 0) {
+        fuse_log(FUSE_LOG_ERR, "chroot(\"%s\"): %m\n", lo->source);
+        exit(1);
+    }
+
+    /* Move into the chroot */
+    if (chdir("/") != 0) {
+        fuse_log(FUSE_LOG_ERR, "chdir(\"/\"): %m\n");
+        exit(1);
+    }
+}
+
+/*
  * Lock down this process to prevent access to other processes or files outside
  * source directory.  This reduces the impact of arbitrary code execution bugs.
  */
 static void setup_sandbox(struct lo_data *lo, struct fuse_session *se,
                           bool enable_syslog)
 {
-    setup_namespaces(lo, se);
-    setup_mounts(lo->source);
+    if (lo->sandbox == SANDBOX_NAMESPACE) {
+        setup_namespaces(lo, se);
+        setup_mounts(lo->source);
+    } else {
+        setup_chroot(lo);
+    }
+
     setup_seccomp(enable_syslog);
     setup_capabilities(g_strdup(lo->modcaps));
 }
@@ -2806,6 +3387,8 @@ static void fuse_lo_data_cleanup(struct lo_data *lo)
         close(lo->root.fd);
     }
 
+    free(lo->xattrmap);
+    free_xattrmap(lo);
     free(lo->source);
 }
 
@@ -2815,6 +3398,7 @@ int main(int argc, char *argv[])
     struct fuse_session *se;
     struct fuse_cmdline_opts opts;
     struct lo_data lo = {
+        .sandbox = SANDBOX_NAMESPACE,
         .debug = 0,
         .writeback = 0,
         .posix_lock = 0,
@@ -2878,12 +3462,11 @@ int main(int argc, char *argv[])
         goto err_out1;
     }
 
-    /*
-     * log_level is 0 if not configured via cmd options (0 is LOG_EMERG,
-     * and we don't use this log level).
-     */
     if (opts.log_level != 0) {
         current_log_level = opts.log_level;
+    } else {
+        /* default log level is INFO */
+        current_log_level = FUSE_LOG_INFO;
     }
     lo.debug = opts.debug;
     if (lo.debug) {
@@ -2906,6 +3489,11 @@ int main(int argc, char *argv[])
     } else {
         lo.source = strdup("/");
     }
+
+    if (lo.xattrmap) {
+        parse_xattrmap(&lo);
+    }
+
     if (!lo.timeout_set) {
         switch (lo.cache) {
         case CACHE_NONE: