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Re: [Qemu-devel] block: Review of .has_zero_init use

From: Peter Lieven
Subject: Re: [Qemu-devel] block: Review of .has_zero_init use
Date: Wed, 26 Jun 2013 07:59:27 +0200

Am 26.06.2013 um 05:14 schrieb Bharata B Rao <address@hidden>:

> On Tue, Jun 25, 2013 at 01:39:11PM +0200, Kevin Wolf wrote:
>> Can you please review for the gluster, rbd, sheepdog and ssh driver
>> whether it's safe to assume that the image reads back as zeros after
>> bdrv_create?
> Gluster supports both file and block backends. While the above is true for
> file backend (which uses ftruncate), the same is not true for
> block backend (which uses lvcreate & lvresize).
> So overall it is not safe to assume that an image on GlusterFS volume
> reads back as zeroes after create.

Okay, so for safety we have to return has_zero_init = 0. Erroneously assuming
a device is zero initialized can bring severe filesystem corruption.

Do you see a way to query the information of the underlaying
backend from the storage and return 1 or 0 conditionally?


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