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Re: [Qemu-devel] [PATCH 1/6] libqblock APIs
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 1/6] libqblock APIs |
Date: |
Mon, 03 Sep 2012 16:05:06 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 |
Il 03/09/2012 15:56, Eric Blake ha scritto:
> Exactly how does the *pnum argument work? This interface looks like it
> isn't fully thought out yet. Either I want to know if a chunk of
> sectors is allocated (I supply start and length of sectors to check),
> regardless of how many sectors beyond that point are also allocated
> (pnum makes no sense);
pnum makes sense if the [start, start+length) range includes both
allocated and unallocated sectors.
> or I want to know how many sectors are allocated
> from a given point (I supply start, and the function returns length, so
> nb_sectors makes no sense).
This operation could be O(number of blocks in disk) worst case, so it
makes sense to provide nb_sectors as an upper bound. nb_sectors is
typically dictated by the size of your buffer.
That said, QEMU's internal bdrv_is_allocated function does have one not
entirely appealing property: the block at start + *pnum might have the
same state as the block at start + *pnum - 1, even if *pnum < length.
We may want to work around this in libqblock, but we could also simply
document it.
Paolo
> Either way, I think you are supplying too
> many parameters for how I envision checking for allocated sectors.
- [Qemu-devel] [PATCH 0/6] libqblock, qemu block layer library, Wenchao Xia, 2012/09/03
- Re: [Qemu-devel] [PATCH 1/6] libqblock APIs, Eric Blake, 2012/09/03
- Re: [Qemu-devel] [PATCH 1/6] libqblock APIs, Wenchao Xia, 2012/09/04
- Re: [Qemu-devel] [PATCH 1/6] libqblock APIs, Eric Blake, 2012/09/04
- Re: [Qemu-devel] [PATCH 1/6] libqblock APIs, Paolo Bonzini, 2012/09/04
Re: [Qemu-devel] [PATCH 1/6] libqblock APIs, Blue Swirl, 2012/09/03
[Qemu-devel] [PATCH 3/6] libqblock error handling, Wenchao Xia, 2012/09/03