Re: [PATCH] copy: adjust fiemap handling of sparse files

[Pádraig Brady]

On 10/02/11 10:01, Pádraig Brady wrote:
> $ fallocate -l $((1<<29)) /tmp/t.f
> $ strace -e _llseek cp-before /tmp/t.f /dev/null 2>&1 | wc -l
> 180
> $ strace -e _llseek cp /tmp/t.f /dev/null 2>&1 | wc -l
> 0
> 
> Hmm, the above suggests to me that we could use the
> FIEMAP_EXTENT_UNWRITTEN flag, so as to skip the read()
> for these allocated but unwritten (zero) extents.
> We could treat such extents like holes, except we
> would only generate holes in the dest with SPARSE_ALWAYS.

First pass at the above attached.
I still need to check on BTRFS etc.
and I can probably clean up the code a bit more

cheers,
Pádraig.

fiemap-empty.diff
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