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Date: Wed, 4 Jun 2014 14:41:48 +0200
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20140604124148.GE11073@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [RFC 4/5] block: Add AIO followers
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To: Max Reitz <mreitz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Fam Zheng <famz@redhat.com>, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Sat, May 31, 2014 at 08:43:11PM +0200, Max Reitz wrote:
> If a long-running operation on a BDS wants to always remain in the same
> AIO context, it somehow needs to keep track of the BDS changing its
> context. This adds a function for registering callbacks on a BDS which
> are called whenever the BDS is attached or detached from an AIO context.
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c                   | 55 +++++++++++++++++++++++++++++++++++++++++++++++
>  include/block/block_int.h | 40 ++++++++++++++++++++++++++++++++++
>  2 files changed, 95 insertions(+)

Great, we definitely need this mechanism.  Block jobs can also use it
later.

Usually QEMU calls this a "notifier" rather than a "follower".  For
example, see include/qemu/notifier.h and bdrv_add_close_notifier().

Stefan