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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5368E1AA.2080609@redhat.com \
--to=pbonzini@redhat.com \
--cc=kwolf@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=stefanha@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.