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[Qemu-devel] Qemu-img convert with -B
From: |
Brad Campbell |
Subject: |
[Qemu-devel] Qemu-img convert with -B |
Date: |
Wed, 27 Apr 2011 11:05:48 +0800 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.14) Gecko/20110223 Lightning/1.0b2 Thunderbird/3.1.8 |
G'day all,
I see there is a bug raised about the behaviour of qemu-img when used to
convert using an output backing file. It allocates every sector whether
or not it already exists in the output backing file.
I'm walking my way through the block driver to try and get a handle on
why this is the case.
The comment in qemu-img.c is :
/* If the output image is being created as a copy on
write image,
copy all sectors even the ones containing only NUL
bytes,
because they may differ from the sectors in the base
image.
Can someone verify these assumptions for me please?
- I can bdrv_open() a file that has a chain of backing files, and the
following is true :
- bdrv_read() returns the most recently allocated sector contents (or 0)
- bdrv_is_allocated() will return false only if that sector is not
allocated in _any_ of the files in the chain
If these assumptions are true, can anyone see a logical error in
bdrv_open() both the input file and the out_baseimg, and where sectors
are allocated comparing them to see if the are the same. If so, not
allocating those in the output file?
I'm assuming the comment above is to allow for the case that someone
specifies the output backing file being different from the last input
backing file.
Am I missing something?
Regards,
Brad
- [Qemu-devel] Qemu-img convert with -B,
Brad Campbell <=
- Re: [Qemu-devel] Qemu-img convert with -B, Stefan Hajnoczi, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Brad Campbell, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Kevin Wolf, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Brad Campbell, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Kevin Wolf, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Brad Campbell, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Brad Campbell, 2011/04/27
- Re: [Qemu-devel] Qemu-img convert with -B, Kevin Wolf, 2011/04/28
- Re: [Qemu-devel] Qemu-img convert with -B, Brad Campbell, 2011/04/28