docs/system: put qemu-block-drivers body in an included file

This removes the "only" directives, and lets us use the conventional
"DESCRIPTION" section in the manpage.

This temporarily drops the qemu-block-drivers documentation
from the system manual, but it will be put back (in the
right place in the toctree) in a later commit.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200228153619.9906-14-peter.maydell@linaro.org
Message-id: 20200226113034.6741-14-pbonzini@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: Added commit message note about temporarily losing
qemu-block-drivers from the system manual]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 954 insertions, 0 deletions

diff --git a/docs/system/qemu-block-drivers.rst.inc b/docs/system/qemu-block-drivers.rst.inc
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+Disk image file formats
+~~~~~~~~~~~~~~~~~~~~~~~
+
+QEMU supports many image file formats that can be used with VMs as well as with
+any of the tools (like ``qemu-img``). This includes the preferred formats
+raw and qcow2 as well as formats that are supported for compatibility with
+older QEMU versions or other hypervisors.
+
+Depending on the image format, different options can be passed to
+``qemu-img create`` and ``qemu-img convert`` using the ``-o`` option.
+This section describes each format and the options that are supported for it.
+
+.. program:: image-formats
+.. option:: raw
+
+  Raw disk image format. This format has the advantage of
+  being simple and easily exportable to all other emulators. If your
+  file system supports *holes* (for example in ext2 or ext3 on
+  Linux or NTFS on Windows), then only the written sectors will reserve
+  space. Use ``qemu-img info`` to know the real size used by the
+  image or ``ls -ls`` on Unix/Linux.
+
+  Supported options:
+
+  .. program:: raw
+  .. option:: preallocation
+
+    Preallocation mode (allowed values: ``off``, ``falloc``,
+    ``full``). ``falloc`` mode preallocates space for image by
+    calling ``posix_fallocate()``. ``full`` mode preallocates space
+    for image by writing data to underlying storage. This data may or
+    may not be zero, depending on the storage location.
+
+.. program:: image-formats
+.. option:: qcow2
+
+  QEMU image format, the most versatile format. Use it to have smaller
+  images (useful if your filesystem does not supports holes, for example
+  on Windows), zlib based compression and support of multiple VM
+  snapshots.
+
+  Supported options:
+
+  .. program:: qcow2
+  .. option:: compat
+
+    Determines the qcow2 version to use. ``compat=0.10`` uses the
+    traditional image format that can be read by any QEMU since 0.10.
+    ``compat=1.1`` enables image format extensions that only QEMU 1.1 and
+    newer understand (this is the default). Amongst others, this includes
+    zero clusters, which allow efficient copy-on-read for sparse images.
+
+  .. option:: backing_file
+
+    File name of a base image (see ``create`` subcommand)
+
+  .. option:: backing_fmt
+
+    Image format of the base image
+
+  .. option:: encryption
+
+    This option is deprecated and equivalent to ``encrypt.format=aes``
+
+  .. option:: encrypt.format
+
+    If this is set to ``luks``, it requests that the qcow2 payload (not
+    qcow2 header) be encrypted using the LUKS format. The passphrase to
+    use to unlock the LUKS key slot is given by the ``encrypt.key-secret``
+    parameter. LUKS encryption parameters can be tuned with the other
+    ``encrypt.*`` parameters.
+
+    If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
+    The encryption key is given by the ``encrypt.key-secret`` parameter.
+    This encryption format is considered to be flawed by modern cryptography
+    standards, suffering from a number of design problems:
+
+    - The AES-CBC cipher is used with predictable initialization vectors based
+      on the sector number. This makes it vulnerable to chosen plaintext attacks
+      which can reveal the existence of encrypted data.
+    - The user passphrase is directly used as the encryption key. A poorly
+      chosen or short passphrase will compromise the security of the encryption.
+    - In the event of the passphrase being compromised there is no way to
+      change the passphrase to protect data in any qcow images. The files must
+      be cloned, using a different encryption passphrase in the new file. The
+      original file must then be securely erased using a program like shred,
+      though even this is ineffective with many modern storage technologies.
+
+    The use of this is no longer supported in system emulators. Support only
+    remains in the command line utilities, for the purposes of data liberation
+    and interoperability with old versions of QEMU. The ``luks`` format
+    should be used instead.
+
+  .. option:: encrypt.key-secret
+
+    Provides the ID of a ``secret`` object that contains the passphrase
+    (``encrypt.format=luks``) or encryption key (``encrypt.format=aes``).
+
+  .. option:: encrypt.cipher-alg
+
+    Name of the cipher algorithm and key length. Currently defaults
+    to ``aes-256``. Only used when ``encrypt.format=luks``.
+
+  .. option:: encrypt.cipher-mode
+
+    Name of the encryption mode to use. Currently defaults to ``xts``.
+    Only used when ``encrypt.format=luks``.
+
+  .. option:: encrypt.ivgen-alg
+
+    Name of the initialization vector generator algorithm. Currently defaults
+    to ``plain64``. Only used when ``encrypt.format=luks``.
+
+  .. option:: encrypt.ivgen-hash-alg
+
+    Name of the hash algorithm to use with the initialization vector generator
+    (if required). Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
+
+  .. option:: encrypt.hash-alg
+
+    Name of the hash algorithm to use for PBKDF algorithm
+    Defaults to ``sha256``. Only used when ``encrypt.format=luks``.
+
+  .. option:: encrypt.iter-time
+
+    Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
+    Defaults to ``2000``. Only used when ``encrypt.format=luks``.
+
+  .. option:: cluster_size
+
+    Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster
+    sizes can improve the image file size whereas larger cluster sizes generally
+    provide better performance.
+
+  .. option:: preallocation
+
+    Preallocation mode (allowed values: ``off``, ``metadata``, ``falloc``,
+    ``full``). An image with preallocated metadata is initially larger but can
+    improve performance when the image needs to grow. ``falloc`` and ``full``
+    preallocations are like the same options of ``raw`` format, but sets up
+    metadata also.
+
+  .. option:: lazy_refcounts
+
+    If this option is set to ``on``, reference count updates are postponed with
+    the goal of avoiding metadata I/O and improving performance. This is
+    particularly interesting with :option:`cache=writethrough` which doesn't batch
+    metadata updates. The tradeoff is that after a host crash, the reference count
+    tables must be rebuilt, i.e. on the next open an (automatic) ``qemu-img
+    check -r all`` is required, which may take some time.
+
+    This option can only be enabled if ``compat=1.1`` is specified.
+
+  .. option:: nocow
+
+    If this option is set to ``on``, it will turn off COW of the file. It's only
+    valid on btrfs, no effect on other file systems.
+
+    Btrfs has low performance when hosting a VM image file, even more
+    when the guest on the VM also using btrfs as file system. Turning off
+    COW is a way to mitigate this bad performance. Generally there are two
+    ways to turn off COW on btrfs:
+
+    - Disable it by mounting with nodatacow, then all newly created files
+      will be NOCOW.
+    - For an empty file, add the NOCOW file attribute. That's what this
+      option does.
+
+    Note: this option is only valid to new or empty files. If there is
+    an existing file which is COW and has data blocks already, it couldn't
+    be changed to NOCOW by setting ``nocow=on``. One can issue ``lsattr
+    filename`` to check if the NOCOW flag is set or not (Capital 'C' is
+    NOCOW flag).
+
+.. program:: image-formats
+.. option:: qed
+
+   Old QEMU image format with support for backing files and compact image files
+   (when your filesystem or transport medium does not support holes).
+
+   When converting QED images to qcow2, you might want to consider using the
+   ``lazy_refcounts=on`` option to get a more QED-like behaviour.
+
+   Supported options:
+
+   .. program:: qed
+   .. option:: backing_file
+
+      File name of a base image (see ``create`` subcommand).
+
+   .. option:: backing_fmt
+
+     Image file format of backing file (optional).  Useful if the format cannot be
+     autodetected because it has no header, like some vhd/vpc files.
+
+   .. option:: cluster_size
+
+     Changes the cluster size (must be power-of-2 between 4K and 64K). Smaller
+     cluster sizes can improve the image file size whereas larger cluster sizes
+     generally provide better performance.
+
+   .. option:: table_size
+
+     Changes the number of clusters per L1/L2 table (must be
+     power-of-2 between 1 and 16).  There is normally no need to
+     change this value but this option can between used for
+     performance benchmarking.
+
+.. program:: image-formats
+.. option:: qcow
+
+  Old QEMU image format with support for backing files, compact image files,
+  encryption and compression.
+
+  Supported options:
+
+   .. program:: qcow
+   .. option:: backing_file
+
+     File name of a base image (see ``create`` subcommand)
+
+   .. option:: encryption
+
+     This option is deprecated and equivalent to ``encrypt.format=aes``
+
+   .. option:: encrypt.format
+
+     If this is set to ``aes``, the image is encrypted with 128-bit AES-CBC.
+     The encryption key is given by the ``encrypt.key-secret`` parameter.
+     This encryption format is considered to be flawed by modern cryptography
+     standards, suffering from a number of design problems enumerated previously
+     against the ``qcow2`` image format.
+
+     The use of this is no longer supported in system emulators. Support only
+     remains in the command line utilities, for the purposes of data liberation
+     and interoperability with old versions of QEMU.
+
+     Users requiring native encryption should use the ``qcow2`` format
+     instead with ``encrypt.format=luks``.
+
+   .. option:: encrypt.key-secret
+
+     Provides the ID of a ``secret`` object that contains the encryption
+     key (``encrypt.format=aes``).
+
+.. program:: image-formats
+.. option:: luks
+
+  LUKS v1 encryption format, compatible with Linux dm-crypt/cryptsetup
+
+  Supported options:
+
+  .. program:: luks
+  .. option:: key-secret
+
+    Provides the ID of a ``secret`` object that contains the passphrase.
+
+  .. option:: cipher-alg
+
+    Name of the cipher algorithm and key length. Currently defaults
+    to ``aes-256``.
+
+  .. option:: cipher-mode
+
+    Name of the encryption mode to use. Currently defaults to ``xts``.
+
+  .. option:: ivgen-alg
+
+    Name of the initialization vector generator algorithm. Currently defaults
+    to ``plain64``.
+
+  .. option:: ivgen-hash-alg
+
+    Name of the hash algorithm to use with the initialization vector generator
+    (if required). Defaults to ``sha256``.
+
+  .. option:: hash-alg
+
+    Name of the hash algorithm to use for PBKDF algorithm
+    Defaults to ``sha256``.
+
+  .. option:: iter-time
+
+    Amount of time, in milliseconds, to use for PBKDF algorithm per key slot.
+    Defaults to ``2000``.
+
+.. program:: image-formats
+.. option:: vdi
+
+  VirtualBox 1.1 compatible image format.
+
+  Supported options:
+
+  .. program:: vdi
+  .. option:: static
+
+    If this option is set to ``on``, the image is created with metadata
+    preallocation.
+
+.. program:: image-formats
+.. option:: vmdk
+
+  VMware 3 and 4 compatible image format.
+
+  Supported options:
+
+  .. program: vmdk
+  .. option:: backing_file
+
+    File name of a base image (see ``create`` subcommand).
+
+  .. option:: compat6
+
+    Create a VMDK version 6 image (instead of version 4)
+
+  .. option:: hwversion
+
+    Specify vmdk virtual hardware version. Compat6 flag cannot be enabled
+    if hwversion is specified.
+
+  .. option:: subformat
+
+    Specifies which VMDK subformat to use. Valid options are
+    ``monolithicSparse`` (default),
+    ``monolithicFlat``,
+    ``twoGbMaxExtentSparse``,
+    ``twoGbMaxExtentFlat`` and
+    ``streamOptimized``.
+
+.. program:: image-formats
+.. option:: vpc
+
+  VirtualPC compatible image format (VHD).
+
+  Supported options:
+
+  .. program:: vpc
+  .. option:: subformat
+
+    Specifies which VHD subformat to use. Valid options are
+    ``dynamic`` (default) and ``fixed``.
+
+.. program:: image-formats
+.. option:: VHDX
+
+  Hyper-V compatible image format (VHDX).
+
+  Supported options:
+
+  .. program:: VHDX
+  .. option:: subformat
+
+    Specifies which VHDX subformat to use. Valid options are
+    ``dynamic`` (default) and ``fixed``.
+
+    .. option:: block_state_zero
+
+      Force use of payload blocks of type 'ZERO'.  Can be set to ``on`` (default)
+      or ``off``.  When set to ``off``, new blocks will be created as
+      ``PAYLOAD_BLOCK_NOT_PRESENT``, which means parsers are free to return
+      arbitrary data for those blocks.  Do not set to ``off`` when using
+      ``qemu-img convert`` with ``subformat=dynamic``.
+
+    .. option:: block_size
+
+      Block size; min 1 MB, max 256 MB.  0 means auto-calculate based on
+      image size.
+
+    .. option:: log_size
+
+      Log size; min 1 MB.
+
+Read-only formats
+~~~~~~~~~~~~~~~~~
+
+More disk image file formats are supported in a read-only mode.
+
+.. program:: image-formats
+.. option:: bochs
+
+  Bochs images of ``growing`` type.
+
+.. program:: image-formats
+.. option:: cloop
+
+  Linux Compressed Loop image, useful only to reuse directly compressed
+  CD-ROM images present for example in the Knoppix CD-ROMs.
+
+.. program:: image-formats
+.. option:: dmg
+
+  Apple disk image.
+
+.. program:: image-formats
+.. option:: parallels
+
+  Parallels disk image format.
+
+Using host drives
+~~~~~~~~~~~~~~~~~
+
+In addition to disk image files, QEMU can directly access host
+devices. We describe here the usage for QEMU version >= 0.8.3.
+
+Linux
+^^^^^
+
+On Linux, you can directly use the host device filename instead of a
+disk image filename provided you have enough privileges to access
+it. For example, use ``/dev/cdrom`` to access to the CDROM.
+
+CD
+  You can specify a CDROM device even if no CDROM is loaded. QEMU has
+  specific code to detect CDROM insertion or removal. CDROM ejection by
+  the guest OS is supported. Currently only data CDs are supported.
+
+Floppy
+  You can specify a floppy device even if no floppy is loaded. Floppy
+  removal is currently not detected accurately (if you change floppy
+  without doing floppy access while the floppy is not loaded, the guest
+  OS will think that the same floppy is loaded).
+  Use of the host's floppy device is deprecated, and support for it will
+  be removed in a future release.
+
+Hard disks
+  Hard disks can be used. Normally you must specify the whole disk
+  (``/dev/hdb`` instead of ``/dev/hdb1``) so that the guest OS can
+  see it as a partitioned disk. WARNING: unless you know what you do, it
+  is better to only make READ-ONLY accesses to the hard disk otherwise
+  you may corrupt your host data (use the ``-snapshot`` command
+  line option or modify the device permissions accordingly).
+
+Windows
+^^^^^^^
+
+CD
+  The preferred syntax is the drive letter (e.g. ``d:``). The
+  alternate syntax ``\\.\d:`` is supported. ``/dev/cdrom`` is
+  supported as an alias to the first CDROM drive.
+
+  Currently there is no specific code to handle removable media, so it
+  is better to use the ``change`` or ``eject`` monitor commands to
+  change or eject media.
+
+Hard disks
+  Hard disks can be used with the syntax: ``\\.\PhysicalDriveN``
+  where *N* is the drive number (0 is the first hard disk).
+
+  WARNING: unless you know what you do, it is better to only make
+  READ-ONLY accesses to the hard disk otherwise you may corrupt your
+  host data (use the ``-snapshot`` command line so that the
+  modifications are written in a temporary file).
+
+Mac OS X
+^^^^^^^^
+
+``/dev/cdrom`` is an alias to the first CDROM.
+
+Currently there is no specific code to handle removable media, so it
+is better to use the ``change`` or ``eject`` monitor commands to
+change or eject media.
+
+Virtual FAT disk images
+~~~~~~~~~~~~~~~~~~~~~~~
+
+QEMU can automatically create a virtual FAT disk image from a
+directory tree. In order to use it, just type:
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -hdb fat:/my_directory
+
+Then you access access to all the files in the ``/my_directory``
+directory without having to copy them in a disk image or to export
+them via SAMBA or NFS. The default access is *read-only*.
+
+Floppies can be emulated with the ``:floppy:`` option:
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -fda fat:floppy:/my_directory
+
+A read/write support is available for testing (beta stage) with the
+``:rw:`` option:
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -fda fat:floppy:rw:/my_directory
+
+What you should *never* do:
+
+- use non-ASCII filenames
+- use "-snapshot" together with ":rw:"
+- expect it to work when loadvm'ing
+- write to the FAT directory on the host system while accessing it with the guest system
+
+NBD access
+~~~~~~~~~~
+
+QEMU can access directly to block device exported using the Network Block Device
+protocol.
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -hdb nbd://my_nbd_server.mydomain.org:1024/
+
+If the NBD server is located on the same host, you can use an unix socket instead
+of an inet socket:
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -hdb nbd+unix://?socket=/tmp/my_socket
+
+In this case, the block device must be exported using qemu-nbd:
+
+.. parsed-literal::
+
+  qemu-nbd --socket=/tmp/my_socket my_disk.qcow2
+
+The use of qemu-nbd allows sharing of a disk between several guests:
+
+.. parsed-literal::
+
+  qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2
+
+and then you can use it with two guests:
+
+.. parsed-literal::
+
+  |qemu_system| linux1.img -hdb nbd+unix://?socket=/tmp/my_socket
+  |qemu_system| linux2.img -hdb nbd+unix://?socket=/tmp/my_socket
+
+If the nbd-server uses named exports (supported since NBD 2.9.18, or with QEMU's
+own embedded NBD server), you must specify an export name in the URI:
+
+.. parsed-literal::
+
+  |qemu_system| -cdrom nbd://localhost/debian-500-ppc-netinst
+  |qemu_system| -cdrom nbd://localhost/openSUSE-11.1-ppc-netinst
+
+The URI syntax for NBD is supported since QEMU 1.3.  An alternative syntax is
+also available.  Here are some example of the older syntax:
+
+.. parsed-literal::
+
+  |qemu_system| linux.img -hdb nbd:my_nbd_server.mydomain.org:1024
+  |qemu_system| linux2.img -hdb nbd:unix:/tmp/my_socket
+  |qemu_system| -cdrom nbd:localhost:10809:exportname=debian-500-ppc-netinst
+
+
+
+Sheepdog disk images
+~~~~~~~~~~~~~~~~~~~~
+
+Sheepdog is a distributed storage system for QEMU.  It provides highly
+available block level storage volumes that can be attached to
+QEMU-based virtual machines.
+
+You can create a Sheepdog disk image with the command:
+
+.. parsed-literal::
+
+  qemu-img create sheepdog:///IMAGE SIZE
+
+where *IMAGE* is the Sheepdog image name and *SIZE* is its
+size.
+
+To import the existing *FILENAME* to Sheepdog, you can use a
+convert command.
+
+.. parsed-literal::
+
+  qemu-img convert FILENAME sheepdog:///IMAGE
+
+You can boot from the Sheepdog disk image with the command:
+
+.. parsed-literal::
+
+  |qemu_system| sheepdog:///IMAGE
+
+You can also create a snapshot of the Sheepdog image like qcow2.
+
+.. parsed-literal::
+
+  qemu-img snapshot -c TAG sheepdog:///IMAGE
+
+where *TAG* is a tag name of the newly created snapshot.
+
+To boot from the Sheepdog snapshot, specify the tag name of the
+snapshot.
+
+.. parsed-literal::
+
+  |qemu_system| sheepdog:///IMAGE#TAG
+
+You can create a cloned image from the existing snapshot.
+
+.. parsed-literal::
+
+  qemu-img create -b sheepdog:///BASE#TAG sheepdog:///IMAGE
+
+where *BASE* is an image name of the source snapshot and *TAG*
+is its tag name.
+
+You can use an unix socket instead of an inet socket:
+
+.. parsed-literal::
+
+  |qemu_system| sheepdog+unix:///IMAGE?socket=PATH
+
+If the Sheepdog daemon doesn't run on the local host, you need to
+specify one of the Sheepdog servers to connect to.
+
+.. parsed-literal::
+
+  qemu-img create sheepdog://HOSTNAME:PORT/IMAGE SIZE
+  |qemu_system| sheepdog://HOSTNAME:PORT/IMAGE
+
+iSCSI LUNs
+~~~~~~~~~~
+
+iSCSI is a popular protocol used to access SCSI devices across a computer
+network.
+
+There are two different ways iSCSI devices can be used by QEMU.
+
+The first method is to mount the iSCSI LUN on the host, and make it appear as
+any other ordinary SCSI device on the host and then to access this device as a
+/dev/sd device from QEMU. How to do this differs between host OSes.
+
+The second method involves using the iSCSI initiator that is built into
+QEMU. This provides a mechanism that works the same way regardless of which
+host OS you are running QEMU on. This section will describe this second method
+of using iSCSI together with QEMU.
+
+In QEMU, iSCSI devices are described using special iSCSI URLs. URL syntax:
+
+::
+
+  iscsi://[<username>[%<password>]@]<host>[:<port>]/<target-iqn-name>/<lun>
+
+Username and password are optional and only used if your target is set up
+using CHAP authentication for access control.
+Alternatively the username and password can also be set via environment
+variables to have these not show up in the process list:
+
+::
+
+  export LIBISCSI_CHAP_USERNAME=<username>
+  export LIBISCSI_CHAP_PASSWORD=<password>
+  iscsi://<host>/<target-iqn-name>/<lun>
+
+Various session related parameters can be set via special options, either
+in a configuration file provided via '-readconfig' or directly on the
+command line.
+
+If the initiator-name is not specified qemu will use a default name
+of 'iqn.2008-11.org.linux-kvm[:<uuid>'] where <uuid> is the UUID of the
+virtual machine. If the UUID is not specified qemu will use
+'iqn.2008-11.org.linux-kvm[:<name>'] where <name> is the name of the
+virtual machine.
+
+Setting a specific initiator name to use when logging in to the target:
+
+::
+
+  -iscsi initiator-name=iqn.qemu.test:my-initiator
+
+Controlling which type of header digest to negotiate with the target:
+
+::
+
+  -iscsi header-digest=CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+
+These can also be set via a configuration file:
+
+::
+
+  [iscsi]
+    user = "CHAP username"
+    password = "CHAP password"
+    initiator-name = "iqn.qemu.test:my-initiator"
+    # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+    header-digest = "CRC32C"
+
+Setting the target name allows different options for different targets:
+
+::
+
+  [iscsi "iqn.target.name"]
+    user = "CHAP username"
+    password = "CHAP password"
+    initiator-name = "iqn.qemu.test:my-initiator"
+    # header digest is one of CRC32C|CRC32C-NONE|NONE-CRC32C|NONE
+    header-digest = "CRC32C"
+
+How to use a configuration file to set iSCSI configuration options:
+
+.. parsed-literal::
+
+  cat >iscsi.conf <<EOF
+  [iscsi]
+    user = "me"
+    password = "my password"
+    initiator-name = "iqn.qemu.test:my-initiator"
+    header-digest = "CRC32C"
+  EOF
+
+  |qemu_system| -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
+    -readconfig iscsi.conf
+
+How to set up a simple iSCSI target on loopback and access it via QEMU:
+this example shows how to set up an iSCSI target with one CDROM and one DISK
+using the Linux STGT software target. This target is available on Red Hat based
+systems as the package 'scsi-target-utils'.
+
+.. parsed-literal::
+
+  tgtd --iscsi portal=127.0.0.1:3260
+  tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.qemu.test
+  tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 \\
+      -b /IMAGES/disk.img --device-type=disk
+  tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 2 \\
+      -b /IMAGES/cd.iso --device-type=cd
+  tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
+
+  |qemu_system| -iscsi initiator-name=iqn.qemu.test:my-initiator \\
+    -boot d -drive file=iscsi://127.0.0.1/iqn.qemu.test/1 \\
+    -cdrom iscsi://127.0.0.1/iqn.qemu.test/2
+
+GlusterFS disk images
+~~~~~~~~~~~~~~~~~~~~~
+
+GlusterFS is a user space distributed file system.
+
+You can boot from the GlusterFS disk image with the command:
+
+URI:
+
+.. parsed-literal::
+
+  |qemu_system| -drive file=gluster[+TYPE]://[HOST}[:PORT]]/VOLUME/PATH
+                               [?socket=...][,file.debug=9][,file.logfile=...]
+
+JSON:
+
+.. parsed-literal::
+
+  |qemu_system| 'json:{"driver":"qcow2",
+                           "file":{"driver":"gluster",
+                                    "volume":"testvol","path":"a.img","debug":9,"logfile":"...",
+                                    "server":[{"type":"tcp","host":"...","port":"..."},
+                                              {"type":"unix","socket":"..."}]}}'
+
+*gluster* is the protocol.
+
+*TYPE* specifies the transport type used to connect to gluster
+management daemon (glusterd). Valid transport types are
+tcp and unix. In the URI form, if a transport type isn't specified,
+then tcp type is assumed.
+
+*HOST* specifies the server where the volume file specification for
+the given volume resides. This can be either a hostname or an ipv4 address.
+If transport type is unix, then *HOST* field should not be specified.
+Instead *socket* field needs to be populated with the path to unix domain
+socket.
+
+*PORT* is the port number on which glusterd is listening. This is optional
+and if not specified, it defaults to port 24007. If the transport type is unix,
+then *PORT* should not be specified.
+
+*VOLUME* is the name of the gluster volume which contains the disk image.
+
+*PATH* is the path to the actual disk image that resides on gluster volume.
+
+*debug* is the logging level of the gluster protocol driver. Debug levels
+are 0-9, with 9 being the most verbose, and 0 representing no debugging output.
+The default level is 4. The current logging levels defined in the gluster source
+are 0 - None, 1 - Emergency, 2 - Alert, 3 - Critical, 4 - Error, 5 - Warning,
+6 - Notice, 7 - Info, 8 - Debug, 9 - Trace
+
+*logfile* is a commandline option to mention log file path which helps in
+logging to the specified file and also help in persisting the gfapi logs. The
+default is stderr.
+
+You can create a GlusterFS disk image with the command:
+
+.. parsed-literal::
+
+  qemu-img create gluster://HOST/VOLUME/PATH SIZE
+
+Examples
+
+.. parsed-literal::
+
+  |qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img
+  |qemu_system| -drive file=gluster+tcp://1.2.3.4/testvol/a.img
+  |qemu_system| -drive file=gluster+tcp://1.2.3.4:24007/testvol/dir/a.img
+  |qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]/testvol/dir/a.img
+  |qemu_system| -drive file=gluster+tcp://[1:2:3:4:5:6:7:8]:24007/testvol/dir/a.img
+  |qemu_system| -drive file=gluster+tcp://server.domain.com:24007/testvol/dir/a.img
+  |qemu_system| -drive file=gluster+unix:///testvol/dir/a.img?socket=/tmp/glusterd.socket
+  |qemu_system| -drive file=gluster+rdma://1.2.3.4:24007/testvol/a.img
+  |qemu_system| -drive file=gluster://1.2.3.4/testvol/a.img,file.debug=9,file.logfile=/var/log/qemu-gluster.log
+  |qemu_system| 'json:{"driver":"qcow2",
+                           "file":{"driver":"gluster",
+                                    "volume":"testvol","path":"a.img",
+                                    "debug":9,"logfile":"/var/log/qemu-gluster.log",
+                                    "server":[{"type":"tcp","host":"1.2.3.4","port":24007},
+                                              {"type":"unix","socket":"/var/run/glusterd.socket"}]}}'
+  |qemu_system| -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
+                                       file.debug=9,file.logfile=/var/log/qemu-gluster.log,
+                                       file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
+                                       file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
+
+Secure Shell (ssh) disk images
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+You can access disk images located on a remote ssh server
+by using the ssh protocol:
+
+.. parsed-literal::
+
+  |qemu_system| -drive file=ssh://[USER@]SERVER[:PORT]/PATH[?host_key_check=HOST_KEY_CHECK]
+
+Alternative syntax using properties:
+
+.. parsed-literal::
+
+  |qemu_system| -drive file.driver=ssh[,file.user=USER],file.host=SERVER[,file.port=PORT],file.path=PATH[,file.host_key_check=HOST_KEY_CHECK]
+
+*ssh* is the protocol.
+
+*USER* is the remote user.  If not specified, then the local
+username is tried.
+
+*SERVER* specifies the remote ssh server.  Any ssh server can be
+used, but it must implement the sftp-server protocol.  Most Unix/Linux
+systems should work without requiring any extra configuration.
+
+*PORT* is the port number on which sshd is listening.  By default
+the standard ssh port (22) is used.
+
+*PATH* is the path to the disk image.
+
+The optional *HOST_KEY_CHECK* parameter controls how the remote
+host's key is checked.  The default is ``yes`` which means to use
+the local ``.ssh/known_hosts`` file.  Setting this to ``no``
+turns off known-hosts checking.  Or you can check that the host key
+matches a specific fingerprint:
+``host_key_check=md5:78:45:8e:14:57:4f:d5:45:83:0a:0e:f3:49:82:c9:c8``
+(``sha1:`` can also be used as a prefix, but note that OpenSSH
+tools only use MD5 to print fingerprints).
+
+Currently authentication must be done using ssh-agent.  Other
+authentication methods may be supported in future.
+
+Note: Many ssh servers do not support an ``fsync``-style operation.
+The ssh driver cannot guarantee that disk flush requests are
+obeyed, and this causes a risk of disk corruption if the remote
+server or network goes down during writes.  The driver will
+print a warning when ``fsync`` is not supported:
+
+::
+
+  warning: ssh server ssh.example.com:22 does not support fsync
+
+With sufficiently new versions of libssh and OpenSSH, ``fsync`` is
+supported.
+
+NVMe disk images
+~~~~~~~~~~~~~~~~
+
+NVM Express (NVMe) storage controllers can be accessed directly by a userspace
+driver in QEMU.  This bypasses the host kernel file system and block layers
+while retaining QEMU block layer functionalities, such as block jobs, I/O
+throttling, image formats, etc.  Disk I/O performance is typically higher than
+with ``-drive file=/dev/sda`` using either thread pool or linux-aio.
+
+The controller will be exclusively used by the QEMU process once started. To be
+able to share storage between multiple VMs and other applications on the host,
+please use the file based protocols.
+
+Before starting QEMU, bind the host NVMe controller to the host vfio-pci
+driver.  For example:
+
+.. parsed-literal::
+
+  # modprobe vfio-pci
+  # lspci -n -s 0000:06:0d.0
+  06:0d.0 0401: 1102:0002 (rev 08)
+  # echo 0000:06:0d.0 > /sys/bus/pci/devices/0000:06:0d.0/driver/unbind
+  # echo 1102 0002 > /sys/bus/pci/drivers/vfio-pci/new_id
+
+  # |qemu_system| -drive file=nvme://HOST:BUS:SLOT.FUNC/NAMESPACE
+
+Alternative syntax using properties:
+
+.. parsed-literal::
+
+  |qemu_system| -drive file.driver=nvme,file.device=HOST:BUS:SLOT.FUNC,file.namespace=NAMESPACE
+
+*HOST*:*BUS*:*SLOT*.\ *FUNC* is the NVMe controller's PCI device
+address on the host.
+
+*NAMESPACE* is the NVMe namespace number, starting from 1.
+
+Disk image file locking
+~~~~~~~~~~~~~~~~~~~~~~~
+
+By default, QEMU tries to protect image files from unexpected concurrent
+access, as long as it's supported by the block protocol driver and host
+operating system. If multiple QEMU processes (including QEMU emulators and
+utilities) try to open the same image with conflicting accessing modes, all but
+the first one will get an error.
+
+This feature is currently supported by the file protocol on Linux with the Open
+File Descriptor (OFD) locking API, and can be configured to fall back to POSIX
+locking if the POSIX host doesn't support Linux OFD locking.
+
+To explicitly enable image locking, specify "locking=on" in the file protocol
+driver options. If OFD locking is not possible, a warning will be printed and
+the POSIX locking API will be used. In this case there is a risk that the lock
+will get silently lost when doing hot plugging and block jobs, due to the
+shortcomings of the POSIX locking API.
+
+QEMU transparently handles lock handover during shared storage migration.  For
+shared virtual disk images between multiple VMs, the "share-rw" device option
+should be used.
+
+By default, the guest has exclusive write access to its disk image. If the
+guest can safely share the disk image with other writers the
+``-device ...,share-rw=on`` parameter can be used.  This is only safe if
+the guest is running software, such as a cluster file system, that
+coordinates disk accesses to avoid corruption.
+
+Note that share-rw=on only declares the guest's ability to share the disk.
+Some QEMU features, such as image file formats, require exclusive write access
+to the disk image and this is unaffected by the share-rw=on option.
+
+Alternatively, locking can be fully disabled by "locking=off" block device
+option. In the command line, the option is usually in the form of
+"file.locking=off" as the protocol driver is normally placed as a "file" child
+under a format driver. For example:
+
+::
+
+  -blockdev driver=qcow2,file.filename=/path/to/image,file.locking=off,file.driver=file
+
+To check if image locking is active, check the output of the "lslocks" command
+on host and see if there are locks held by the QEMU process on the image file.
+More than one byte could be locked by the QEMU instance, each byte of which
+reflects a particular permission that is acquired or protected by the running
+block driver.