From 40055951a7afbfc037c6c7351d72a5c5d83ed99b Mon Sep 17 00:00:00 2001 From: Max Reitz Date: Tue, 22 Jul 2014 22:58:42 +0200 Subject: qemu-img: Allow source cache mode specification Many qemu-img subcommands only read the source file(s) once. For these use cases, a full write-back cache is unnecessary and mainly clutters host cache memory. Though this is generally no concern as cache memory is freely available and can be scaled by the host OS, it may become a concern with thin provisioning. For these cases, it makes sense to allow users to freely specify the source cache mode (e.g. use no cache at all). This commit adds a new switch (-T) for the qemu-img subcommands check, compare, convert and rebase to specify the cache to be used for source images (the backing file in case of rebase). Signed-off-by: Max Reitz Reviewed-by: Eric Blake Signed-off-by: Kevin Wolf --- qemu-img.texi | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) (limited to 'qemu-img.texi') diff --git a/qemu-img.texi b/qemu-img.texi index 514be90f7d..688b28d87b 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -72,6 +72,9 @@ down to the nearest 512 bytes. You may use the common size suffixes like 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} +in contrast specifies the cache mode that should be used with the source +file(s). @end table Parameters to snapshot subcommand: @@ -113,7 +116,7 @@ Skip the creation of the target volume 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}. @@ -172,7 +175,7 @@ the backing file, the backing file will not be truncated. If you want the 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} +@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. @@ -213,7 +216,7 @@ Error on reading data @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} @@ -325,7 +328,7 @@ source code. 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. @@ -336,6 +339,9 @@ The backing file is changed to @var{backing_file} and (if the image format of 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 the new backing file. + There are two different modes in which @code{rebase} can operate: @table @option @item Safe mode -- cgit v1.2.1