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Re: [Qemu-devel] [PATCH 3/4] block/parallels: Don't update header until
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH 3/4] block/parallels: Don't update header until the first actual write |
Date: |
Fri, 27 Oct 2017 11:09:19 +0200 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 27.10.2017 um 10:57 hat Jeff Cody geschrieben:
> The on disk image format 'inuse' header field is updated blindly if the
> image is opened RDWR. This can cause problems if the QEMU runstate is
> set to INMIGRATE, at which point the underlying file is set to INACTIVE.
> This causes an assert in bdrv_co_pwritev().
>
> Do something similar to what is done in VHDX; latch the first write, and
> update the header the first time we modify the file.
>
> Signed-off-by: Jeff Cody <address@hidden>
For VHDX, it seems that we have to have the header update in the write
path anyway, so it might be justifiable, but I think for parallels, it's
just ugly.
The conservative approach to this would be doing the header write in
.bdrv_open() only if BDRV_O_INACTIVE is cleared, and otherwise do it
during .bdrv_invalidate_cache().
By the way, random design thought: It might make sense to change
.bdrv_open() so that it always opens inactive images and then call
.bdrv_invalidate_cache() (possibly renamed to .bdrv_activate())
unconditionally even without migration.
Kevin