doc: Document driver-specific -blockdev options
This documents the driver-specific options for the raw, qcow2 and file block drivers for the man page. For everything else, we refer to the QAPI documentation. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
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qemu-options.hx
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qemu-options.hx
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@ -614,7 +614,18 @@ STEXI
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@item -blockdev @var{option}[,@var{option}[,@var{option}[,...]]]
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@item -blockdev @var{option}[,@var{option}[,@var{option}[,...]]]
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@findex -blockdev
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@findex -blockdev
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Define a new block driver node.
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Define a new block driver node. Some of the options apply to all block drivers,
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other options are only accepted for a specific block driver. See below for a
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list of generic options and options for the most common block drivers.
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Options that expect a reference to another node (e.g. @code{file}) can be
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given in two ways. Either you specify the node name of an already existing node
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(file=@var{node-name}), or you define a new node inline, adding options
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for the referenced node after a dot (file.filename=@var{path},file.aio=native).
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A block driver node created with @option{-blockdev} can be used for a guest
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device by specifying its node name for the @code{drive} property in a
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@option{-device} argument that defines a block device.
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@table @option
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@table @option
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@item Valid options for any block driver node:
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@item Valid options for any block driver node:
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@ -654,6 +665,108 @@ zero write commands. You may even choose "unmap" if @var{discard} is set
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to "unmap" to allow a zero write to be converted to an @code{unmap} operation.
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to "unmap" to allow a zero write to be converted to an @code{unmap} operation.
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@end table
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@end table
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@item Driver-specific options for @code{file}
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This is the protocol-level block driver for accessing regular files.
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@table @code
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@item filename
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The path to the image file in the local filesystem
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@item aio
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Specifies the AIO backend (threads/native, default: threads)
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@end table
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Example:
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@example
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-blockdev driver=file,node-name=disk,filename=disk.img
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@end example
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@item Driver-specific options for @code{raw}
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This is the image format block driver for raw images. It is usually
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stacked on top of a protocol level block driver such as @code{file}.
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@table @code
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@item file
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Reference to or definition of the data source block driver node
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(e.g. a @code{file} driver node)
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@end table
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Example 1:
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@example
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-blockdev driver=file,node-name=disk_file,filename=disk.img
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-blockdev driver=raw,node-name=disk,file=disk_file
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@end example
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Example 2:
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@example
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-blockdev driver=raw,node-name=disk,file.driver=file,file.filename=disk.img
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@end example
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@item Driver-specific options for @code{qcow2}
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This is the image format block driver for qcow2 images. It is usually
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stacked on top of a protocol level block driver such as @code{file}.
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@table @code
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@item file
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Reference to or definition of the data source block driver node
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(e.g. a @code{file} driver node)
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@item backing
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Reference to or definition of the backing file block device (default is taken
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from the image file). It is allowed to pass an empty string here in order to
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disable the default backing file.
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@item lazy-refcounts
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Whether to enable the lazy refcounts feature (on/off; default is taken from the
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image file)
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@item cache-size
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The maximum total size of the L2 table and refcount block caches in bytes
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(default: 1048576 bytes or 8 clusters, whichever is larger)
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@item l2-cache-size
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The maximum size of the L2 table cache in bytes
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(default: 4/5 of the total cache size)
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@item refcount-cache-size
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The maximum size of the refcount block cache in bytes
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(default: 1/5 of the total cache size)
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@item cache-clean-interval
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Clean unused entries in the L2 and refcount caches. The interval is in seconds.
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The default value is 0 and it disables this feature.
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@item pass-discard-request
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Whether discard requests to the qcow2 device should be forwarded to the data
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source (on/off; default: on if discard=unmap is specified, off otherwise)
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@item pass-discard-snapshot
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Whether discard requests for the data source should be issued when a snapshot
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operation (e.g. deleting a snapshot) frees clusters in the qcow2 file (on/off;
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default: on)
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@item pass-discard-other
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Whether discard requests for the data source should be issued on other
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occasions where a cluster gets freed (on/off; default: off)
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@item overlap-check
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Which overlap checks to perform for writes to the image
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(none/constant/cached/all; default: cached). For details or finer
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granularity control refer to the QAPI documentation of @code{blockdev-add}.
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@end table
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Example 1:
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@example
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-blockdev driver=file,node-name=my_file,filename=/tmp/disk.qcow2
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-blockdev driver=qcow2,node-name=hda,file=my_file,overlap-check=none,cache-size=16777216
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@end example
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Example 2:
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@example
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-blockdev driver=qcow2,node-name=disk,file.driver=http,file.filename=http://example.com/image.qcow2
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@end example
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@item Driver-specific options for other drivers
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Please refer to the QAPI documentation of the @code{blockdev-add} QMP command.
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@end table
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@end table
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