From: Kevin Wolf <kwolf@redhat.com>
To: Max Reitz <mreitz@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [PATCH] qcow2: Fix preallocation on block devices
Date: Thu, 7 May 2020 10:39:24 +0200 [thread overview]
Message-ID: <20200507083924.GA6019@linux.fritz.box> (raw)
In-Reply-To: <20200505141801.1096763-1-mreitz@redhat.com>
Am 05.05.2020 um 16:18 hat Max Reitz geschrieben:
> Calling bdrv_getlength() to get the pre-truncate file size will not
> really work on block devices, because they have always the same length,
> and trying to write beyond it will fail with a rather cryptic error
> message.
>
> Instead, we should use qcow2_get_last_cluster() and bdrv_getlength()
> only as a fallback.
>
> Before this patch:
> $ truncate -s 1G test.img
> $ sudo losetup -f --show test.img
> /dev/loop0
> $ sudo qemu-img create -f qcow2 -o preallocation=full /dev/loop0 64M
> Formatting '/dev/loop0', fmt=qcow2 size=67108864 cluster_size=65536
> preallocation=full lazy_refcounts=off refcount_bits=16
> qemu-img: /dev/loop0: Could not resize image: Failed to resize refcount
> structures: No space left on device
>
> With this patch:
> $ sudo qemu-img create -f qcow2 -o preallocation=full /dev/loop0 64M
> Formatting '/dev/loop0', fmt=qcow2 size=67108864 cluster_size=65536
> preallocation=full lazy_refcounts=off refcount_bits=16
> qemu-img: /dev/loop0: Could not resize image: Failed to resize
> underlying file: Preallocation mode 'full' unsupported for this
> non-regular file
>
> So as you can see, it still fails, but now the problem is missing
> support on the block device level, so we at least get a better error
> message.
>
> Note that we cannot preallocate block devices on truncate by design,
> because we do not know what area to preallocate. Their length is always
> the same, the truncate operation does not change it.
>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
Thanks, applied to the block branch.
Kevin
prev parent reply other threads:[~2020-05-07 8:40 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-05 14:18 [PATCH] qcow2: Fix preallocation on block devices Max Reitz
2020-05-07 8:39 ` Kevin Wolf [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200507083924.GA6019@linux.fritz.box \
--to=kwolf@redhat.com \
--cc=mreitz@redhat.com \
--cc=qemu-block@nongnu.org \
--cc=qemu-devel@nongnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).