fix live migration

[qemu.git] / qemu-img.texi

diff --git a/qemu-img.texi b/qemu-img.texi
index 6fc3c28e0d6492bfd61fd03ad9346be48677ac14..60b83fc11a458f4122af805a6f3541cfabd7d03e 100644 (file)
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -4,6 +4,16 @@ usage: qemu-img command [command options]
 @c man end
 @end example
 
+@c man begin DESCRIPTION
+qemu-img allows you to create, convert and modify images offline. It can handle
+all image formats supported by QEMU.
+
+@b{Warning:} Never use qemu-img to modify images in use by a running virtual
+machine or any other process; this may destroy the image. Also, be aware that
+querying an image that is being modified by another process may encounter
+inconsistent state.
+@c man end
+
 @c man begin OPTIONS
 
 The following commands are supported:
@@ -18,6 +28,10 @@ Command parameters:
 is the disk image format. It is guessed automatically in most cases. See below
 for a description of the supported disk formats.
 
+@item --backing-chain
+will enumerate information about backing files in a disk image chain. Refer
+below for further description.
+
 @item size
 is the disk image size in bytes. Optional suffixes @code{k} or @code{K}
 (kilobyte, 1024) @code{M} (megabyte, 1024k) and @code{G} (gigabyte, 1024M)
@@ -70,10 +84,15 @@ lists all snapshots in the given image
 Command description:
 
 @table @option
-@item check [-f @var{fmt}] @var{filename}
+@item check [-f @var{fmt}] [-r [leaks | all]] @var{filename}
 
 Perform a consistency check on the disk image @var{filename}.
 
+If @code{-r} is specified, qemu-img tries to repair any inconsistencies found
+during the check. @code{-r leaks} repairs only cluster leaks, whereas
+@code{-r all} fixes all kinds of errors, with a higher risk of choosing the
+wrong fix or hiding corruption that has already occurred.
+
 Only the formats @code{qcow2}, @code{qed} and @code{vdi} support
 consistency checks.
 
@@ -114,12 +133,28 @@ created as a copy on write image of the specified base image; the
 @var{backing_file} should have the same content as the input's base image,
 however the path, image format, etc may differ.
 
-@item info [-f @var{fmt}] @var{filename}
+@item info [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] @var{filename}
 
 Give information about the disk image @var{filename}. Use it in
 particular to know the size reserved on disk which can be different
 from the displayed size. If VM snapshots are stored in the disk image,
-they are displayed too.
+they are displayed too. The command can output in the format @var{ofmt}
+which is either @code{human} or @code{json}.
+
+If a disk image has a backing file chain, information about each disk image in
+the chain can be recursively enumerated by using the option @code{--backing-chain}.
+
+For instance, if you have an image chain like:
+
+@example
+base.qcow2 <- snap1.qcow2 <- snap2.qcow2
+@end example
+
+To enumerate information about each disk image in the above chain, starting from top to base, do:
+
+@example
+qemu-img info --backing-chain snap2.qcow2
+@end example
 
 @item snapshot [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot} ] @var{filename}
 
@@ -132,7 +167,9 @@ Changes the backing file of an image. Only the formats @code{qcow2} and
 
 The backing file is changed to @var{backing_file} and (if the image format of
 @var{filename} supports this) the backing file format is changed to
-@var{backing_fmt}.
+@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty
+string), then the image is rebased onto no backing file (i.e. it will exist
+independently of any backing file).
 
 There are two different modes in which @code{rebase} can operate:
 @table @option
@@ -232,6 +269,29 @@ to grow.
 
 @end table
 
+@item qed
+Image format with support for backing files and compact image files (when your
+filesystem or transport medium does not support holes).  Good performance due
+to less metadata than the more featureful qcow2 format, especially with
+cache=writethrough or cache=directsync.  Consider using qcow2 which will soon
+have a similar optimization and is most actively developed.
+
+Supported options:
+@table @code
+@item backing_file
+File name of a base image (see @option{create} subcommand).
+@item 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.
+@item 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.
+@item 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 be
+used for performance benchmarking.
+@end table
 
 @item qcow
 Old QEMU image format. Left for compatibility.