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When preallocating an encrypted qcow2 image, it just lets the protocol
driver write data and then does not mark the clusters as zero.
Therefore, reading this image will yield effectively random data.
As such, we have not fulfilled the promise of always writing zeroes when
preallocating an image in a while. It seems that nobody has really
cared, so change the documentation to conform to qemu's actual behavior.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190711132935.13070-1-mreitz@redhat.com
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
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This adds a salvaging mode (--salvage) to qemu-img convert which ignores
read errors and treats the respective areas as containing only zeroes.
This can be used for instance to at least partially recover the data
from terminally corrupted qcow2 images.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-id: 20190507203508.18026-3-mreitz@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
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Ideally, it should be self-explanatory. However, keys like "disk size"
arguably really are not self-explanatory. In any case, there is no harm
in going into a some more detail here.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Just writing that --output=json outputs JSON information does not really
help; we should also make a note of what QAPI type the result object
has. (The map subcommand does not emit a QAPI-typed object, but its
section already describes the object structure well enough.)
Signed-off-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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It turns out that having options listed in three places continues to be
a bad idea. I'm still toying with the idea of an improved infrastructure
here, but in the meantime, another bandaid.
There are three locations:
(1) .hx file, formatted as texi
(2) .hx file, formatted as human readable.
(3) .texi file, as section headers, formatted as texi.
You can compare the two summaries within the .hx file like so:
Human-readable command summaries:
`./qemu-img --help | grep 'Command syntax' -A14`
Detokenized texi command summaries:
`grep "@item" qemu-img-cmds.hx | sed -E 's|@var\{([^\}]*?)\}|\1|g'`
You can compare the two separate texi summaries like so:
Texi command summaries:
`grep "@item" qemu-img-cmds.hx"`
Texi command headers:
grep -E "@item.*@var" qemu-img.texi | tail -14
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 20190409210655.777-1-jsnow@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This reverts commit eb461485f4558e362fab905735b50987505bca44.
Now that we introduce an explicit option, these implicit rules are not
used.
Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Explicitly enabling zero detection or compression suppresses copy
offloading during convert. Document it.
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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It has been marked as deprecated since QEMU v2.0 already, so it
is time now to finally remove it.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-id: 1528288551-31641-1-git-send-email-thuth@redhat.com
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
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These are also different and out of order for whatever reason.
I'd like to automate this in the future, but for now let's put
on the band-aid.
In the case of resize, there were options missing from all
three docstrings; the new string is based on the code.
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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This should match the summary ordering, which is alphabetical.
Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Split options out of the "@table @var" section and create a "@table
@option", then use whitespaces and blank lines consistently.
Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kashyap Chamarthy <kchamart@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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qemu-img commit invalidates all images between base and top. This
should be mentioned in the man page.
Suggested-by: Ping Li <pingl@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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The flag is additional precaution against data loss. Perhaps in the future the
operation shrink without this flag will be blocked for all formats, but for now
we need to maintain compatibility with raw.
Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20170918124230.8152-2-pbutsykin@virtuozzo.com
[mreitz: Added a missing space to a warning]
Signed-off-by: Max Reitz <mreitz@redhat.com>
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It's not too surprising when a user specifies the backing file relative
to the current working directory instead of the top layer image. This
causes error when they differ. Though the error message has enough
information to infer the fact about the misunderstanding, it is better
if we document this explicitly, so that users don't have to learn from
mistakes.
Signed-off-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Or, rather, force the open of a backing image if one was specified
for creation. Using a similar -unsafe option as rebase, allow qemu-img
to ignore the backing file validation if possible.
It may not always be possible, as in the existing case when a filesize
for the new image was not specified.
This is accomplished by shifting around the conditionals in
bdrv_img_create, such that a backing file is always opened unless we
provide BDRV_O_NO_BACKING. qemu-img is adjusted to pass this new flag
when -u is provided to create.
Sorry for the heinous looking diffstat, but it's mostly whitespace.
Inspired by: https://bugzilla.redhat.com/show_bug.cgi?id=1213786
Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Add a --preallocation command line option to qemu-img resize which can
be used to set the PreallocMode parameter of blk_truncate().
While touching this code, fix the fact that we did not handle errors
returned by blk_getlength().
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20170613202107.10125-5-mreitz@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
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The measure subcommand calculates the size required by a new image file.
This can be used by users or management tools that need to allocate
space on an LVM volume, SAN LUN, etc before creating or converting an
image file.
Suggested-by: Maor Lipchuk <mlipchuk@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Message-id: 20170705125738.8777-8-stefanha@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
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Document that use of guest virtual sector numbers as the basis for
the initialization vectors is a potential weakness, when combined
with internal snapshots or multiple images using the same passphrase.
This fixes the formatting of the itemized list too.
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170623162419.26068-4-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
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The '--image-opts' flag indicates whether the source filename
includes options. The target filename has to remain in the
plain filename format though, since it needs to be passed to
bdrv_create(). When using --skip-create though, it would be
possible to use image-opts syntax. This adds --target-image-opts
to indicate that the target filename includes options. Currently
this mandates use of the --skip-create flag too.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170515164712.6643-4-berrange@redhat.com
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
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Currently we only print progress information on retrieval of SIGUSR1.
Some systems have a dedicated SIGINFO for this, however, so it should be
handled appropriately if it is available.
Buglink: https://bugs.launchpad.net/qemu/+bug/1662468
Signed-off-by: Max Reitz <mreitz@redhat.com>
Message-id: 20170207235757.2026-1-mreitz@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
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The create and convert subcommands have shorthands to set the
backing_file and, in the case of create, the backing_fmt options for the
new image. However, they have not been documented so far, which is
remedied by this patch.
Reported-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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the convert process is currently completely implemented with sync operations.
That means it reads one buffer and then writes it. No parallelism and each sync
request takes as long as it takes until it is completed.
This can be a big performance hit when the convert process reads and writes
to devices which do not benefit from kernel readahead or pagecache.
In our environment we heavily have the following two use cases when using
qemu-img convert.
a) reading from NFS and writing to iSCSI for deploying templates
b) reading from iSCSI and writing to NFS for backups
In both processes we use libiscsi and libnfs so we have no kernel cache.
This patch changes the convert process to work with parallel running coroutines
which can significantly improve performance for network storage devices:
qemu-img (master)
nfs -> iscsi 22.8 secs
nfs -> ram 11.7 secs
ram -> iscsi 12.3 secs
qemu-img-async (8 coroutines, in-order write disabled)
nfs -> iscsi 11.0 secs
nfs -> ram 10.4 secs
ram -> iscsi 9.0 secs
This patches introduces 2 new cmdline parameters. The -m parameter to specify
the number of coroutines running in parallel (defaults to 8). And the -W parameter to
allow qemu-img to write to the target out of order rather than sequential. This improves
performance as the writes do not have to wait for each other to complete.
Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This adds the skip option which allows qemu-img dd to skip a number of blocks
before copying the input.
A test case was added to test the skip option.
Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
Message-id: 20160810141609.32727-1-fullmanet@gmail.com
Signed-off-by: Max Reitz <mreitz@redhat.com>
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This patch adds a basic dd subcommand analogous to dd(1) to qemu-img.
For the start, this implements the bs, if, of and count options and requires
both if and of to be specified (no stdin/stdout if not specified) and doesn't
support tty, pipes, etc.
The image format must be specified with -O for the output if the raw format
is not the intended one.
Two tests are added to test qemu-img dd.
Signed-off-by: Reda Sallahi <fullmanet@gmail.com>
Message-id: 20160810024312.14544-1-fullmanet@gmail.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
[mreitz: Moved test 158 to 170]
Signed-off-by: Max Reitz <mreitz@redhat.com>
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The command will work this way:
qemu-img --trace "qcow2*" create -f qcow2 1.img 64G
[Quote "qcow2*" to protect against shell globbing as suggested by Eric
Blake <eblake@redhat.com>.
--Stefan]
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1466174654-30130-8-git-send-email-den@openvz.org
Suggested by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This is necessary to enable creation of common qemu-img options which will
be specified before command.
The patch also enables '-V' alias to '--version' (exactly like in other
block utilities) and documents this change.
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1466174654-30130-7-git-send-email-den@openvz.org
CC: Paolo Bonzini <pbonzini@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This options allows to flush the image periodically during write tests.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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With this new option, qemu-img bench can be told to advance the current
offset after each request by a different value than the buffer size.
This is useful for controlling the conditions for cluster allocation in
image formats (e.g. qcow2 cluster allocation with COW in front of the
request, or COW areas that aren't overwritten immediately).
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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This patch adds an option the specify the offset of the first request
made by qemu-img bench. This allows to benchmark misaligned requests.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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This extends qemu-img bench with an option that makes it use sequential
writes instead of reads for the test run.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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This adds a qemu-img command that allows doing some simple benchmarks
for the block layer without involving guest devices and a real VM.
For the start, this implements only a test of sequential reads.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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Currently qemu-img allows an image filename to be passed on the
command line, but unless using the JSON format, it does not have
a way to set any options except the format eg
qemu-img info https://127.0.0.1/images/centos7.iso
This adds a --image-opts arg that indicates that the positional
filename should be interpreted as a full option string, not
just a filename.
qemu-img info --image-opts driver=https,url=https://127.0.0.1/images,sslverify=off
This flag is mutually exclusive with the '-f' / '-F' flags.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Allow creation of user creatable object types with qemu-img
via a new --object command line arg. This will be used to supply
passwords and/or encryption keys to the various block driver
backends via the recently added 'secret' object type.
# printf letmein > mypasswd.txt
# qemu-img info --object secret,id=sec0,file=mypasswd.txt \
...other info args...
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>
Message-Id: <1452718226-25001-1-git-send-email-sitsofe@yahoo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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Many source files have doubled words (eg "the the", "to to",
and so on). Most of these can simply be removed, but a couple
were actual mis-spellings (eg "to to" instead of "to do").
There was even one triple word score "to to to" :-)
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
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Now that bdrv_amend_options() supports a status callback, use it to
display a progress report.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Benoît Canet <benoit.canet@nodalink.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1414404776-4919-3-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Introduce a new parameter for qemu-img commit which may be used to
explicitly specify the backing file into which an image should be
committed if the backing chain has more than a single layer.
[Applied Eric Blake's qemu-img.texi documentation rewording
--Stefan]
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1414159063-25977-12-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Implement progress output for the commit command by querying the
progress of the block job.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1414159063-25977-11-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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After the top image has been committed, it should be emptied unless
specified otherwise.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1414159063-25977-10-git-send-email-mreitz@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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This patch removes support for the cow file format.
Normally we do not break backwards compatibility but in this case there
is no impact and it is the most logical option. Extraordinary claims
require extraordinary evidence so I will show why removing the cow block
driver is the right thing to do.
The cow file format is the disk image format for Usermode Linux, a way
of running a Linux system in userspace. The performance of UML was
never great and it was hacky, but it enjoyed some popularity before
hardware virtualization support became mainstream.
QEMU's block/cow.c is supposed to read this image file format.
Unfortunately the file format was underspecified:
1. Earlier Linux versions used the MAXPATHLEN constant for the backing
filename field. The value of MAXPATHLEN can change, so Linux
switched to a 4096 literal but QEMU has a 1024 literal.
2. Padding was not used on the header struct (both in the Linux kernel
and in QEMU) so the struct layout varied across architectures. In
particular, i386 and x86_64 were different due to int64_t alignment
differences. Linux now uses __attribute__((packed)), QEMU does not.
Therefore:
1. QEMU cow images do not conform to the Linux cow image file format.
2. cow images cannot be shared between different host architectures.
This means QEMU cow images are useless and QEMU has not had bug reports
from users actually hitting these issues.
Let's get rid of this thing, it serves no purpose and no one will be
affected.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1410877464-20481-1-git-send-email-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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preallocation=falloc allocates disk space by posix_fallocate(),
preallocation=full allocates disk space by writing zeros to disk.
Both modes imply preallocation=metadata.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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This patch adds a new option preallocation for raw format, and implements
falloc and full preallocation.
Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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The src_cache option (-T) specifies the cache mode for backing files.
It applies both the image's old backing file as well as the new backing
file:
ret = bdrv_open(&bs_old_backing, backing_name, NULL, NULL, src_flags,
old_backing_drv, &local_err);
if (ret) {
...
}
if (out_baseimg[0]) {
bs_new_backing = bdrv_new("new_backing", &error_abort);
ret = bdrv_open(&bs_new_backing, out_baseimg, NULL, NULL, src_flags,
new_backing_drv, &local_err);
if (ret) {
...
}
}
The documentation only mentions the new backing file but it really
applies to both.
Suggested-by: Jeff Nelson <jenelson@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
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The source cache option takes the same values as the cache option. The
documentation reads a little strange because it starts with "In contrast
the src_cache option ...". The fact that this is comparing with the
previous documented option (the 'cache' option) is implicit. Readers
may be confused, especially if they jump to src_cache without reading
cache documentation first.
Suggested-by: Jeff Nelson <jenelson@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
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qemu-img amend may extensively modify the target image, depending on the
options to be amended (e.g. conversion to qcow2 compat level 0.10 from
1.1 for an image with many unallocated zero clusters). Therefore it
makes sense to allow the user to specify the cache mode to be used.
Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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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 <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Chunyan Liu <cyliu@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Add 'nocow' option so that users could have a chance to set NOCOW flag to
newly created files. It's useful on btrfs file system to enhance performance.
Btrfs has low performance when hosting VM images, even more when the guest
in those VM are also using btrfs as file system. One way to mitigate this bad
performance is to turn off COW attributes on VM files. Generally, there are
two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
all newly created files will be NOCOW. b) per file. Add the NOCOW file
attribute. It could only be done to empty or new files.
This patch tries the second way, according to the option, it could add NOCOW
per file.
For most block drivers, since the create file step is in raw-posix.c, so we
can do setting NOCOW flag ioctl in raw-posix.c only.
But there are some exceptions, like block/vpc.c and block/vdi.c, they are
creating file by calling qemu_open directly. For them, do the same setting
NOCOW flag ioctl work in them separately.
[Fixed up 082.out due to the new 'nocow' creation option
--Stefan]
Signed-off-by: Chunyan Liu <cyliu@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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