specifies the cache mode that should be used with the (destination) file. See
the documentation of the emulator's @code{-drive cache=...} option for allowed
values.
+@item -T @var{src_cache}
+specifies the cache mode that should be used with the source file(s). See
+the documentation of the emulator's @code{-drive cache=...} option for allowed
+values.
@end table
Parameters to snapshot subcommand:
Command description:
@table @option
-@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] @var{filename}
+@item check [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] @var{filename}
Perform a consistency check on the disk image @var{filename}. The command can
output in the format @var{ofmt} which is either @code{human} or @code{json}.
The size can also be specified using the @var{size} option with @code{-o},
it doesn't need to be specified separately in this case.
-@item commit [-f @var{fmt}] [-t @var{cache}] @var{filename}
+@item commit [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
Commit the changes recorded in @var{filename} in its base image or backing file.
If the backing file is smaller than the snapshot, then the backing file will be
backing file to match the size of the smaller snapshot, you can safely truncate
it yourself once the commit operation successfully completes.
-@item compare [-f @var{fmt}] [-F @var{fmt}] [-p] [-s] [-q] @var{filename1} @var{filename2}
+The image @var{filename} is emptied after the operation has succeeded. If you do
+not need @var{filename} afterwards and intend to drop it, you may skip emptying
+@var{filename} by specifying the @code{-d} flag.
+
+If the backing chain of the given image file @var{filename} has more than one
+layer, the backing file into which the changes will be committed may be
+specified as @var{base} (which has to be part of @var{filename}'s backing
+chain). If @var{base} is not specified, the immediate backing file of the top
+image (which is @var{filename}) will be used. For reasons of consistency,
+explicitly specifying @var{base} will always imply @code{-d} (since emptying an
+image after committing to an indirect backing file would lead to different data
+being read from the image due to content in the intermediate backing chain
+overruling the commit target).
+
+@item compare [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-s] [-q] @var{filename1} @var{filename2}
Check if two images have the same content. You can compare images with
different format or settings.
@end table
-@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
+@item convert [-c] [-p] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-o @var{options}] [-s @var{snapshot_id_or_name}] [-l @var{snapshot_param}] [-S @var{sparse_size}] @var{filename} [@var{filename2} [...]] @var{output_filename}
Convert the disk image @var{filename} or a snapshot @var{snapshot_param}(@var{snapshot_id_or_name} is deprecated)
to disk image @var{output_filename} using format @var{output_fmt}. It can be optionally compressed (@code{-c}
rewritten, then it is rewritten as uncompressed data.
Image conversion is also useful to get smaller image when using a
-growable format such as @code{qcow} or @code{cow}: the empty sectors
-are detected and suppressed from the destination image.
+growable format such as @code{qcow}: the empty sectors are detected and
+suppressed from the destination image.
@var{sparse_size} indicates the consecutive number of bytes (defaults to 4k)
that must contain only zeros for qemu-img to create a sparse image during
List, apply, create or delete snapshots in image @var{filename}.
-@item rebase [-f @var{fmt}] [-t @var{cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
+@item rebase [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
Changes the backing file of an image. Only the formats @code{qcow2} and
@code{qed} support changing the backing file.
string), then the image is rebased onto no backing file (i.e. it will exist
independently of any backing file).
+@var{cache} specifies the cache mode to be used for @var{filename}, whereas
+@var{src_cache} specifies the cache mode for reading backing files.
+
There are two different modes in which @code{rebase} can operate:
@table @option
@item Safe mode
partitioning tools inside the VM to actually begin using the new space on the
device.
-@item amend [-f @var{fmt}] -o @var{options} @var{filename}
+@item amend [-p] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}
Amends the image format specific @var{options} for the image file
@var{filename}. Not all file formats support this operation.
space. Use @code{qemu-img info} to know the real size used by the
image or @code{ls -ls} on Unix/Linux.
+Supported options:
+@table @code
+@item preallocation
+Preallocation mode (allowed values: @code{off}, @code{falloc}, @code{full}).
+@code{falloc} mode preallocates space for image by calling posix_fallocate().
+@code{full} mode preallocates space for image by writing zeros to underlying
+storage.
+@end table
+
@item qcow2
QEMU image format, the most versatile format. Use it to have smaller
images (useful if your filesystem does not supports holes, for example
provide better performance.
@item preallocation
-Preallocation mode (allowed values: off, metadata). An image with preallocated
-metadata is initially larger but can improve performance when the image needs
-to grow.
+Preallocation mode (allowed values: @code{off}, @code{metadata}, @code{falloc},
+@code{full}). An image with preallocated metadata is initially larger but can
+improve performance when the image needs to grow. @code{falloc} and @code{full}
+preallocations are like the same options of @code{raw} format, but sets up
+metadata also.
@item lazy_refcounts
If this option is set to @code{on}, reference count updates are postponed with
This option can only be enabled if @code{compat=1.1} is specified.
@item nocow
-If this option is set to @code{on}, it will trun off COW of the file. It's only
+If this option is set to @code{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
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 @code{nocow=on}. One can issue @code{lsattr filename} to check if
-the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).
+the NOCOW flag is set or not (Capital 'C' is NOCOW flag).
@end table
projects / mirror_qemu.git / blobdiff