Re: [Qemu-devel] Re: qemu disk on vfat

[Jim C. Brown]

On Mon, May 08, 2006 at 08:36:15PM -0500, Anthony Liguori wrote:
> Jim C. Brown wrote:
> >Aactually, the bug is in vfat not in qemu-img.
> >
>
> Not really.  POSIX doesn't mandate that ftruncate() increase a file
> size.  This is a Linux-ism and is only valid for filesystems that
> support holes (which vfat doesn't).
>
> Regards,
>
> Anthony Liguori
>

Ok, so in that case this is something qemu-img should handle on its own then.
(Since we're not likely to see a "fix" in either glibc or the kernel for this,
and it has the potential to be a portability issue.)

On Mon, May 08, 2006 at 07:50:24PM -0400, Jim C. Brown wrote:
> qemu-img correctly uses ftruncate() which is suppose to make the file sparse
> if the underlying filesystem supports it, but it should fall back to adding 
> zeros
> to the end of the file. On vfat you aren't able to seek past the end of a file
> period, so this doesn't work.

Turns out I was wrong about this too.

http://www.mail-archive.com/address@hidden/msg00556.html

Here is a patch that silently handles the Linux/vfat case using lseek().

-- 
Infinite complexity begets infinite beauty.
Infinite precision begets infinite perfection.

block.patch
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