From: Paolo Bonzini <pbonzini@redhat.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org, stefanha@redhat.com
Subject: Re: [Qemu-devel] [PATCH v5 12/21] block: define get_block_status return value
Date: Tue, 06 May 2014 15:20:42 +0200 [thread overview]
Message-ID: <5368E1AA.2080609@redhat.com> (raw)
In-Reply-To: <20140506130829.GD3941@noname.str.redhat.com>
Il 06/05/2014 15:08, Kevin Wolf ha scritto:
>> This is true, because bdrv_get_block_status does not ask the backing
>> file whether it is zero in the backing file. Thus, reading from the
>> backing file does not guarantee to read zeroes.
>
> Aha, this paragraph is the key. :-)
>
> I assumed that bdrv_get_block_status() does ask the backing file, but
> apparently it doesn't. The current meaning of BDRV_BLOCK_ZERO is
> therefore not simply "sectors read as zero", but "sectors read as zero
> and this is determined by bs itself (mostly, except for the backing file
> size)".
Exactly.
> Is it a good idea to rely on this or would it be reasonable for
> bdrv_get_block_status() to look at the backing file for returning ZERO
> sometime in the future? I think that could be useful information in some
> cases.
It is reasonable, for example SCSI emulation could use it. However, it
would be a different API (like bdrv_is_allocated_above). It would be
very similar to get_block_status() in qemu-img.c.
Paolo
next prev parent reply other threads:[~2014-05-06 13:20 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-04 17:00 [Qemu-devel] [PATCH v5 00/21] Add qemu-img subcommand to dump file metadata Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 01/21] cow: make reads go at a decent speed Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 02/21] cow: make writes go at a less indecent speed Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 03/21] cow: do not call bdrv_co_is_allocated Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 04/21] block: keep bs->total_sectors up to date even for growable block devices Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 05/21] block: make bdrv_co_is_allocated static Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 06/21] block: do not use ->total_sectors in bdrv_co_is_allocated Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 07/21] block: remove bdrv_is_allocated_above/bdrv_co_is_allocated_above distinction Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 08/21] block: expect errors from bdrv_co_is_allocated Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 09/21] qemu-img: always probe the input image for allocated sectors Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 10/21] block: make bdrv_has_zero_init return false for copy-on-write-images Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 11/21] block: introduce bdrv_get_block_status API Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 12/21] block: define get_block_status return value Paolo Bonzini
2014-05-05 14:34 ` Kevin Wolf
2014-05-05 14:58 ` Paolo Bonzini
2014-05-06 11:34 ` Kevin Wolf
2014-05-06 12:31 ` Paolo Bonzini
2014-05-06 13:08 ` Kevin Wolf
2014-05-06 13:20 ` Paolo Bonzini [this message]
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 13/21] block: return get_block_status data and flags for formats Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 14/21] block: use bdrv_has_zero_init to return BDRV_BLOCK_ZERO Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 15/21] block: return BDRV_BLOCK_ZERO past end of backing file Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 16/21] qemu-img: add a "map" subcommand Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 17/21] docs, qapi: document qemu-img map Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 18/21] raw-posix: return get_block_status data and flags Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 19/21] raw-posix: report unwritten extents as zero Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 20/21] block: add default get_block_status implementation for protocols Paolo Bonzini
2013-09-04 17:00 ` [Qemu-devel] [PATCH v5 21/21] block: look for zero blocks in bs->file Paolo Bonzini
2013-09-05 13:55 ` [Qemu-devel] [PATCH v5 00/21] Add qemu-img subcommand to dump file metadata Stefan Hajnoczi
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