Revision e35bdc123a4ace9f4d3fccaaf88907014e2438cd authored by Kevin Wolf on 05 October 2018, 16:57:40 UTC, committed by Kevin Wolf on 05 November 2018, 14:09:55 UTC
If a management application builds the block graph node by node, the protocol layer doesn't inherit its read-only option from the format layer any more, so it must be set explicitly. Backing files should work on read-only storage, but at the same time, a block job like commit should be able to reopen them read-write if they are on read-write storage. However, without option inheritance, reopen only changes the read-only option for the root node (typically the format layer), but not the protocol layer, so reopening fails (the format layer wants to get write permissions, but the protocol layer is still read-only). A simple workaround for the problem in the management tool would be to open the protocol layer always read-write and to make only the format layer read-only for backing files. However, sometimes the file is actually stored on read-only storage and we don't know whether the image can be opened read-write (for example, for NBD it depends on the server we're trying to connect to). This adds an option that makes QEMU try to open the image read-write, but allows it to degrade to a read-only mode without returning an error. The documentation for this option is consciously phrased in a way that allows QEMU to switch to a better model eventually: Instead of trying when the image is first opened, making the read-only flag dynamic and changing it automatically whenever the first BLK_PERM_WRITE user is attached or the last one is detached would be much more useful behaviour. Unfortunately, this more useful behaviour is also a lot harder to implement, and libvirt needs a solution now before it can switch to -blockdev, so let's start with this easier approach for now. Instead of adding a new auto-read-only option, turning the existing read-only into an enum (with a bool alternate for compatibility) was considered, but it complicated the implementation to the point that it didn't seem to be worth it. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com>
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qemu-img-cmds.hx
HXCOMM Keep the list of subcommands sorted by name.
HXCOMM Use DEFHEADING() to define headings in both help text and texi
HXCOMM Text between STEXI and ETEXI are copied to texi version and
HXCOMM discarded from C version
HXCOMM DEF(command, callback, arg_string) is used to construct
HXCOMM command structures and help message.
HXCOMM HXCOMM can be used for comments, discarded from both texi and C
HXCOMM When amending the TEXI sections, please remember to copy the usage
HXCOMM over to the per-command sections in qemu-img.texi.
STEXI
@table @option
ETEXI
DEF("amend", img_amend,
"amend [--object objectdef] [--image-opts] [-p] [-q] [-f fmt] [-t cache] -o options filename")
STEXI
@item amend [--object @var{objectdef}] [--image-opts] [-p] [-q] [-f @var{fmt}] [-t @var{cache}] -o @var{options} @var{filename}
ETEXI
DEF("bench", img_bench,
"bench [-c count] [-d depth] [-f fmt] [--flush-interval=flush_interval] [-n] [--no-drain] [-o offset] [--pattern=pattern] [-q] [-s buffer_size] [-S step_size] [-t cache] [-w] [-U] filename")
STEXI
@item bench [-c @var{count}] [-d @var{depth}] [-f @var{fmt}] [--flush-interval=@var{flush_interval}] [-n] [--no-drain] [-o @var{offset}] [--pattern=@var{pattern}] [-q] [-s @var{buffer_size}] [-S @var{step_size}] [-t @var{cache}] [-w] [-U] @var{filename}
ETEXI
DEF("check", img_check,
"check [--object objectdef] [--image-opts] [-q] [-f fmt] [--output=ofmt] [-r [leaks | all]] [-T src_cache] [-U] filename")
STEXI
@item check [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [--output=@var{ofmt}] [-r [leaks | all]] [-T @var{src_cache}] [-U] @var{filename}
ETEXI
DEF("commit", img_commit,
"commit [--object objectdef] [--image-opts] [-q] [-f fmt] [-t cache] [-b base] [-d] [-p] filename")
STEXI
@item commit [--object @var{objectdef}] [--image-opts] [-q] [-f @var{fmt}] [-t @var{cache}] [-b @var{base}] [-d] [-p] @var{filename}
ETEXI
DEF("compare", img_compare,
"compare [--object objectdef] [--image-opts] [-f fmt] [-F fmt] [-T src_cache] [-p] [-q] [-s] [-U] filename1 filename2")
STEXI
@item compare [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-F @var{fmt}] [-T @var{src_cache}] [-p] [-q] [-s] [-U] @var{filename1} @var{filename2}
ETEXI
DEF("convert", img_convert,
"convert [--object objectdef] [--image-opts] [--target-image-opts] [-U] [-C] [-c] [-p] [-q] [-n] [-f fmt] [-t cache] [-T src_cache] [-O output_fmt] [-B backing_file] [-o options] [-l snapshot_param] [-S sparse_size] [-m num_coroutines] [-W] filename [filename2 [...]] output_filename")
STEXI
@item convert [--object @var{objectdef}] [--image-opts] [--target-image-opts] [-U] [-c] [-p] [-q] [-n] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-O @var{output_fmt}] [-B @var{backing_file}] [-o @var{options}] [-l @var{snapshot_param}] [-S @var{sparse_size}] [-m @var{num_coroutines}] [-W] @var{filename} [@var{filename2} [...]] @var{output_filename}
ETEXI
DEF("create", img_create,
"create [--object objectdef] [-q] [-f fmt] [-b backing_file] [-F backing_fmt] [-u] [-o options] filename [size]")
STEXI
@item create [--object @var{objectdef}] [-q] [-f @var{fmt}] [-b @var{backing_file}] [-F @var{backing_fmt}] [-u] [-o @var{options}] @var{filename} [@var{size}]
ETEXI
DEF("dd", img_dd,
"dd [--image-opts] [-U] [-f fmt] [-O output_fmt] [bs=block_size] [count=blocks] [skip=blocks] if=input of=output")
STEXI
@item dd [--image-opts] [-U] [-f @var{fmt}] [-O @var{output_fmt}] [bs=@var{block_size}] [count=@var{blocks}] [skip=@var{blocks}] if=@var{input} of=@var{output}
ETEXI
DEF("info", img_info,
"info [--object objectdef] [--image-opts] [-f fmt] [--output=ofmt] [--backing-chain] [-U] filename")
STEXI
@item info [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [--backing-chain] [-U] @var{filename}
ETEXI
DEF("map", img_map,
"map [--object objectdef] [--image-opts] [-f fmt] [--output=ofmt] [-U] filename")
STEXI
@item map [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--output=@var{ofmt}] [-U] @var{filename}
ETEXI
DEF("measure", img_measure,
"measure [--output=ofmt] [-O output_fmt] [-o options] [--size N | [--object objectdef] [--image-opts] [-f fmt] [-l snapshot_param] filename]")
STEXI
@item measure [--output=@var{ofmt}] [-O @var{output_fmt}] [-o @var{options}] [--size @var{N} | [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [-l @var{snapshot_param}] @var{filename}]
ETEXI
DEF("snapshot", img_snapshot,
"snapshot [--object objectdef] [--image-opts] [-U] [-q] [-l | -a snapshot | -c snapshot | -d snapshot] filename")
STEXI
@item snapshot [--object @var{objectdef}] [--image-opts] [-U] [-q] [-l | -a @var{snapshot} | -c @var{snapshot} | -d @var{snapshot}] @var{filename}
ETEXI
DEF("rebase", img_rebase,
"rebase [--object objectdef] [--image-opts] [-U] [-q] [-f fmt] [-t cache] [-T src_cache] [-p] [-u] -b backing_file [-F backing_fmt] filename")
STEXI
@item rebase [--object @var{objectdef}] [--image-opts] [-U] [-q] [-f @var{fmt}] [-t @var{cache}] [-T @var{src_cache}] [-p] [-u] -b @var{backing_file} [-F @var{backing_fmt}] @var{filename}
ETEXI
DEF("resize", img_resize,
"resize [--object objectdef] [--image-opts] [-f fmt] [--preallocation=prealloc] [-q] [--shrink] filename [+ | -]size")
STEXI
@item resize [--object @var{objectdef}] [--image-opts] [-f @var{fmt}] [--preallocation=@var{prealloc}] [-q] [--shrink] @var{filename} [+ | -]@var{size}
ETEXI
STEXI
@end table
ETEXI
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