From: Kevin Wolf <kwolf@redhat.com>
To: Max Reitz <mreitz@redhat.com>
Cc: Jeff Cody <codyprime@gmail.com>, Stefan Weil <sw@weilnetz.de>,
qemu-devel@nongnu.org, qemu-block@nongnu.org,
Stefano Garzarella <sgarzare@redhat.com>
Subject: Re: [Qemu-devel] [PATCH for-4.1? 1/4] qcow2: Fix .bdrv_has_zero_init()
Date: Tue, 16 Jul 2019 18:54:59 +0200 [thread overview]
Message-ID: <20190716165459.GI7297@linux.fritz.box> (raw)
In-Reply-To: <20190715104508.7568-2-mreitz@redhat.com>
Am 15.07.2019 um 12:45 hat Max Reitz geschrieben:
> If a qcow2 file is preallocated, it can no longer guarantee that it
> initially appears as filled with zeroes.
>
> So implement .bdrv_has_zero_init() by checking whether the file is
> preallocated; if so, forward the call to the underlying storage node,
> except for when it is encrypted: Encrypted preallocated images always
> return effectively random data, so .bdrv_has_zero_init() must always
> return 0 for them.
>
> Reported-by: Stefano Garzarella <sgarzare@redhat.com>
> Signed-off-by: Max Reitz <mreitz@redhat.com>
Hm... This patch only really works directly after image creation (which
is indeed where .bdrv_has_zero_init is used). Why do we have to have a
full qcow2_is_zero() that loops over the whole image just to find out
whether it's preallocated? Wouldn't looking at a single data cluster be
enough?
Kevin
next prev parent reply other threads:[~2019-07-16 16:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-15 10:45 [Qemu-devel] [PATCH for-4.1? 0/4] block: Fix three .bdrv_has_zero_init()s Max Reitz
2019-07-15 10:45 ` [Qemu-devel] [PATCH for-4.1? 1/4] qcow2: Fix .bdrv_has_zero_init() Max Reitz
2019-07-16 16:54 ` Kevin Wolf [this message]
2019-07-17 8:37 ` Max Reitz
2019-07-15 10:45 ` [Qemu-devel] [PATCH for-4.1? 2/4] vdi: " Max Reitz
2019-07-15 10:45 ` [Qemu-devel] [PATCH for-4.1? 3/4] vhdx: " Max Reitz
2019-07-15 10:45 ` [Qemu-devel] [PATCH for-4.1? 4/4] iotests: Convert to preallocated encrypted qcow2 Max Reitz
2019-07-15 14:49 ` [Qemu-devel] [PATCH for-4.1? 0/4] block: Fix three .bdrv_has_zero_init()s Stefano Garzarella
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