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-rw-r--r--block/export/export.c4
-rw-r--r--block/export/fuse.c295
-rw-r--r--block/export/meson.build2
3 files changed, 301 insertions, 0 deletions
diff --git a/block/export/export.c b/block/export/export.c
index bad6f21b1c..b716c1522c 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -17,6 +17,7 @@
#include "sysemu/block-backend.h"
#include "sysemu/iothread.h"
#include "block/export.h"
+#include "block/fuse.h"
#include "block/nbd.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-block-export.h"
@@ -31,6 +32,9 @@ static const BlockExportDriver *blk_exp_drivers[] = {
#ifdef CONFIG_VHOST_USER_BLK_SERVER
&blk_exp_vhost_user_blk,
#endif
+#ifdef CONFIG_FUSE
+ &blk_exp_fuse,
+#endif
};
/* Only accessed from the main thread */
diff --git a/block/export/fuse.c b/block/export/fuse.c
new file mode 100644
index 0000000000..0553bcd630
--- /dev/null
+++ b/block/export/fuse.c
@@ -0,0 +1,295 @@
+/*
+ * Present a block device as a raw image through FUSE
+ *
+ * Copyright (c) 2020 Max Reitz <mreitz@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; under version 2 or later of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#define FUSE_USE_VERSION 31
+
+#include "qemu/osdep.h"
+#include "block/aio.h"
+#include "block/block.h"
+#include "block/export.h"
+#include "block/fuse.h"
+#include "block/qapi.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-block.h"
+#include "sysemu/block-backend.h"
+
+#include <fuse.h>
+#include <fuse_lowlevel.h>
+
+
+/* Prevent overly long bounce buffer allocations */
+#define FUSE_MAX_BOUNCE_BYTES (MIN(BDRV_REQUEST_MAX_BYTES, 64 * 1024 * 1024))
+
+
+typedef struct FuseExport {
+ BlockExport common;
+
+ struct fuse_session *fuse_session;
+ struct fuse_buf fuse_buf;
+ bool mounted, fd_handler_set_up;
+
+ char *mountpoint;
+ bool writable;
+} FuseExport;
+
+static GHashTable *exports;
+static const struct fuse_lowlevel_ops fuse_ops;
+
+static void fuse_export_shutdown(BlockExport *exp);
+static void fuse_export_delete(BlockExport *exp);
+
+static void init_exports_table(void);
+
+static int setup_fuse_export(FuseExport *exp, const char *mountpoint,
+ Error **errp);
+static void read_from_fuse_export(void *opaque);
+
+static bool is_regular_file(const char *path, Error **errp);
+
+
+static int fuse_export_create(BlockExport *blk_exp,
+ BlockExportOptions *blk_exp_args,
+ Error **errp)
+{
+ FuseExport *exp = container_of(blk_exp, FuseExport, common);
+ BlockExportOptionsFuse *args = &blk_exp_args->u.fuse;
+ int ret;
+
+ assert(blk_exp_args->type == BLOCK_EXPORT_TYPE_FUSE);
+
+ init_exports_table();
+
+ /*
+ * It is important to do this check before calling is_regular_file() --
+ * that function will do a stat(), which we would have to handle if we
+ * already exported something on @mountpoint. But we cannot, because
+ * we are currently caught up here.
+ * (Note that ideally we would want to resolve relative paths here,
+ * but bdrv_make_absolute_filename() might do the wrong thing for
+ * paths that contain colons, and realpath() would resolve symlinks,
+ * which we do not want: The mount point is not going to be the
+ * symlink's destination, but the link itself.)
+ * So this will not catch all potential clashes, but hopefully at
+ * least the most common one of specifying exactly the same path
+ * string twice.
+ */
+ if (g_hash_table_contains(exports, args->mountpoint)) {
+ error_setg(errp, "There already is a FUSE export on '%s'",
+ args->mountpoint);
+ ret = -EEXIST;
+ goto fail;
+ }
+
+ if (!is_regular_file(args->mountpoint, errp)) {
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ exp->mountpoint = g_strdup(args->mountpoint);
+ exp->writable = blk_exp_args->writable;
+
+ ret = setup_fuse_export(exp, args->mountpoint, errp);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ return 0;
+
+fail:
+ fuse_export_delete(blk_exp);
+ return ret;
+}
+
+/**
+ * Allocates the global @exports hash table.
+ */
+static void init_exports_table(void)
+{
+ if (exports) {
+ return;
+ }
+
+ exports = g_hash_table_new_full(g_str_hash, g_str_equal, g_free, NULL);
+}
+
+/**
+ * Create exp->fuse_session and mount it.
+ */
+static int setup_fuse_export(FuseExport *exp, const char *mountpoint,
+ Error **errp)
+{
+ const char *fuse_argv[4];
+ char *mount_opts;
+ struct fuse_args fuse_args;
+ int ret;
+
+ /* Needs to match what fuse_init() sets. Only max_read must be supplied. */
+ mount_opts = g_strdup_printf("max_read=%zu", FUSE_MAX_BOUNCE_BYTES);
+
+ fuse_argv[0] = ""; /* Dummy program name */
+ fuse_argv[1] = "-o";
+ fuse_argv[2] = mount_opts;
+ fuse_argv[3] = NULL;
+ fuse_args = (struct fuse_args)FUSE_ARGS_INIT(3, (char **)fuse_argv);
+
+ exp->fuse_session = fuse_session_new(&fuse_args, &fuse_ops,
+ sizeof(fuse_ops), exp);
+ g_free(mount_opts);
+ if (!exp->fuse_session) {
+ error_setg(errp, "Failed to set up FUSE session");
+ ret = -EIO;
+ goto fail;
+ }
+
+ ret = fuse_session_mount(exp->fuse_session, mountpoint);
+ if (ret < 0) {
+ error_setg(errp, "Failed to mount FUSE session to export");
+ ret = -EIO;
+ goto fail;
+ }
+ exp->mounted = true;
+
+ g_hash_table_insert(exports, g_strdup(mountpoint), NULL);
+
+ aio_set_fd_handler(exp->common.ctx,
+ fuse_session_fd(exp->fuse_session), true,
+ read_from_fuse_export, NULL, NULL, exp);
+ exp->fd_handler_set_up = true;
+
+ return 0;
+
+fail:
+ fuse_export_shutdown(&exp->common);
+ return ret;
+}
+
+/**
+ * Callback to be invoked when the FUSE session FD can be read from.
+ * (This is basically the FUSE event loop.)
+ */
+static void read_from_fuse_export(void *opaque)
+{
+ FuseExport *exp = opaque;
+ int ret;
+
+ blk_exp_ref(&exp->common);
+
+ do {
+ ret = fuse_session_receive_buf(exp->fuse_session, &exp->fuse_buf);
+ } while (ret == -EINTR);
+ if (ret < 0) {
+ goto out;
+ }
+
+ fuse_session_process_buf(exp->fuse_session, &exp->fuse_buf);
+
+out:
+ blk_exp_unref(&exp->common);
+}
+
+static void fuse_export_shutdown(BlockExport *blk_exp)
+{
+ FuseExport *exp = container_of(blk_exp, FuseExport, common);
+
+ if (exp->fuse_session) {
+ fuse_session_exit(exp->fuse_session);
+
+ if (exp->fd_handler_set_up) {
+ aio_set_fd_handler(exp->common.ctx,
+ fuse_session_fd(exp->fuse_session), true,
+ NULL, NULL, NULL, NULL);
+ exp->fd_handler_set_up = false;
+ }
+ }
+
+ if (exp->mountpoint) {
+ /*
+ * Safe to drop now, because we will not handle any requests
+ * for this export anymore anyway.
+ */
+ g_hash_table_remove(exports, exp->mountpoint);
+ }
+}
+
+static void fuse_export_delete(BlockExport *blk_exp)
+{
+ FuseExport *exp = container_of(blk_exp, FuseExport, common);
+
+ if (exp->fuse_session) {
+ if (exp->mounted) {
+ fuse_session_unmount(exp->fuse_session);
+ }
+
+ fuse_session_destroy(exp->fuse_session);
+ }
+
+ free(exp->fuse_buf.mem);
+ g_free(exp->mountpoint);
+}
+
+/**
+ * Check whether @path points to a regular file. If not, put an
+ * appropriate message into *errp.
+ */
+static bool is_regular_file(const char *path, Error **errp)
+{
+ struct stat statbuf;
+ int ret;
+
+ ret = stat(path, &statbuf);
+ if (ret < 0) {
+ error_setg_errno(errp, errno, "Failed to stat '%s'", path);
+ return false;
+ }
+
+ if (!S_ISREG(statbuf.st_mode)) {
+ error_setg(errp, "'%s' is not a regular file", path);
+ return false;
+ }
+
+ return true;
+}
+
+/**
+ * A chance to set change some parameters supplied to FUSE_INIT.
+ */
+static void fuse_init(void *userdata, struct fuse_conn_info *conn)
+{
+ /*
+ * MIN_NON_ZERO() would not be wrong here, but what we set here
+ * must equal what has been passed to fuse_session_new().
+ * Therefore, as long as max_read must be passed as a mount option
+ * (which libfuse claims will be changed at some point), we have
+ * to set max_read to a fixed value here.
+ */
+ conn->max_read = FUSE_MAX_BOUNCE_BYTES;
+
+ conn->max_write = MIN_NON_ZERO(BDRV_REQUEST_MAX_BYTES, conn->max_write);
+}
+
+static const struct fuse_lowlevel_ops fuse_ops = {
+ .init = fuse_init,
+};
+
+const BlockExportDriver blk_exp_fuse = {
+ .type = BLOCK_EXPORT_TYPE_FUSE,
+ .instance_size = sizeof(FuseExport),
+ .create = fuse_export_create,
+ .delete = fuse_export_delete,
+ .request_shutdown = fuse_export_shutdown,
+};
diff --git a/block/export/meson.build b/block/export/meson.build
index 135b356775..0a08e384c7 100644
--- a/block/export/meson.build
+++ b/block/export/meson.build
@@ -3,3 +3,5 @@ blockdev_ss.add(files('export.c'))
if have_vhost_user_blk_server
blockdev_ss.add(files('vhost-user-blk-server.c'))
endif
+
+blockdev_ss.add(when: fuse, if_true: files('fuse.c'))
generated by cgit v1.2.3-55-g7522 (git 2.39.0) at 2024-12-18 11:52:34 +0100