From 370e8328d7c9e0959c31b3ea97f4a49252333307 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 22 Sep 2016 17:24:38 +0200 Subject: [PATCH] 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 Reviewed-by: Eric Blake Reviewed-by: Max Reitz --- qemu-options.hx | 115 +++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 114 insertions(+), 1 deletion(-) diff --git a/qemu-options.hx b/qemu-options.hx index db20866629..896ff177c3 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -614,7 +614,18 @@ STEXI @item -blockdev @var{option}[,@var{option}[,@var{option}[,...]]] @findex -blockdev -Define a new block driver node. +Define a new block driver node. Some of the options apply to all block drivers, +other options are only accepted for a specific block driver. See below for a +list of generic options and options for the most common block drivers. + +Options that expect a reference to another node (e.g. @code{file}) can be +given in two ways. Either you specify the node name of an already existing node +(file=@var{node-name}), or you define a new node inline, adding options +for the referenced node after a dot (file.filename=@var{path},file.aio=native). + +A block driver node created with @option{-blockdev} can be used for a guest +device by specifying its node name for the @code{drive} property in a +@option{-device} argument that defines a block device. @table @option @item Valid options for any block driver node: @@ -654,6 +665,108 @@ zero write commands. You may even choose "unmap" if @var{discard} is set to "unmap" to allow a zero write to be converted to an @code{unmap} operation. @end table +@item Driver-specific options for @code{file} + +This is the protocol-level block driver for accessing regular files. + +@table @code +@item filename +The path to the image file in the local filesystem +@item aio +Specifies the AIO backend (threads/native, default: threads) +@end table +Example: +@example +-blockdev driver=file,node-name=disk,filename=disk.img +@end example + +@item Driver-specific options for @code{raw} + +This is the image format block driver for raw images. It is usually +stacked on top of a protocol level block driver such as @code{file}. + +@table @code +@item file +Reference to or definition of the data source block driver node +(e.g. a @code{file} driver node) +@end table +Example 1: +@example +-blockdev driver=file,node-name=disk_file,filename=disk.img +-blockdev driver=raw,node-name=disk,file=disk_file +@end example +Example 2: +@example +-blockdev driver=raw,node-name=disk,file.driver=file,file.filename=disk.img +@end example + +@item Driver-specific options for @code{qcow2} + +This is the image format block driver for qcow2 images. It is usually +stacked on top of a protocol level block driver such as @code{file}. + +@table @code +@item file +Reference to or definition of the data source block driver node +(e.g. a @code{file} driver node) + +@item backing +Reference to or definition of the backing file block device (default is taken +from the image file). It is allowed to pass an empty string here in order to +disable the default backing file. + +@item lazy-refcounts +Whether to enable the lazy refcounts feature (on/off; default is taken from the +image file) + +@item cache-size +The maximum total size of the L2 table and refcount block caches in bytes +(default: 1048576 bytes or 8 clusters, whichever is larger) + +@item l2-cache-size +The maximum size of the L2 table cache in bytes +(default: 4/5 of the total cache size) + +@item refcount-cache-size +The maximum size of the refcount block cache in bytes +(default: 1/5 of the total cache size) + +@item cache-clean-interval +Clean unused entries in the L2 and refcount caches. The interval is in seconds. +The default value is 0 and it disables this feature. + +@item pass-discard-request +Whether discard requests to the qcow2 device should be forwarded to the data +source (on/off; default: on if discard=unmap is specified, off otherwise) + +@item pass-discard-snapshot +Whether discard requests for the data source should be issued when a snapshot +operation (e.g. deleting a snapshot) frees clusters in the qcow2 file (on/off; +default: on) + +@item pass-discard-other +Whether discard requests for the data source should be issued on other +occasions where a cluster gets freed (on/off; default: off) + +@item overlap-check +Which overlap checks to perform for writes to the image +(none/constant/cached/all; default: cached). For details or finer +granularity control refer to the QAPI documentation of @code{blockdev-add}. +@end table + +Example 1: +@example +-blockdev driver=file,node-name=my_file,filename=/tmp/disk.qcow2 +-blockdev driver=qcow2,node-name=hda,file=my_file,overlap-check=none,cache-size=16777216 +@end example +Example 2: +@example +-blockdev driver=qcow2,node-name=disk,file.driver=http,file.filename=http://example.com/image.qcow2 +@end example + +@item Driver-specific options for other drivers +Please refer to the QAPI documentation of the @code{blockdev-add} QMP command. + @end table ETEXI