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Re: [Qemu-devel] [Qemu-block] [PATCH v3] block/vdi: Use bdrv_flush after

From: Kevin Wolf
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH v3] block/vdi: Use bdrv_flush after metadata updates
Date: Fri, 8 May 2015 12:43:37 +0200
User-agent: Mutt/1.5.21 (2010-09-15)

Am 07.05.2015 um 06:04 hat Zhe Qiu geschrieben:
> From: phoeagon <address@hidden>
> In reference to 
> b0ad5a455d7e5352d4c86ba945112011dbeadfb8~078a458e077d6b0db262c4b05fee51d01de2d1d2,
>  metadata writes to qcow2/cow/qcow/vpc/vmdk are all synced prior to 
> succeeding writes.

The justification for these patches (in 2010!) was more or less that we
didn't know whether the implementations were safe without the flushes.
Many of the flushes added back then have been removed again until today
because they have turned out to be unnecessary.

> Only when write is successful that bdrv_flush is called.
> Signed-off-by: Zhe Qiu <address@hidden>

Please describe why VDI needs this flush to be safe. This is best done
by describing a case where not doing the flush would lead to image
corruption in case of a crash.

To my knowledge, the VDI driver is completely safe without it.


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