On Mon, Feb 17, 2014 at 04:08:17PM +0100, Lukas Czerner wrote:

Introduce new FALLOC_FL_ZERO_RANGE flag for fallocate. This has the same
functionality as xfs ioctl XFS_IOC_ZERO_RANGE.

It can be used to convert a range of file to zeros preferably without
issuing data IO. Blocks should be preallocated for the regions that span
holes in the file, and the entire range is preferable converted to
unwritten extents - even though file system may choose to zero out the
extent or do whatever which will result in reading zeros from the range
while the range remains allocated for the file.

This can be also used to preallocate blocks past EOF in the same way as
with fallocate. Flag FALLOC_FL_KEEP_SIZE which should cause the inode
size to remain the same.

You can test this feature yourself using xfstests, of fallocate(1) however
you'll need patches for util_linux, xfsprogs and xfstests which you
can find here:

http://people.redhat.com/lczerner/zero_range/

I'll post the patches after we agree and merge the kernel functionality.

I tested this mostly with a subset of xfstests using fsx and fsstress and
even with new generic/290 which is just a copy of xfs/290 usinz fzero
command for xfs_io instead of zero (which uses ioctl). I was testing on
x86_64 and ppc64 with block sizes of 1024, 2048 and 4096.

You also want to convert xfs/242 to be a generic test - it uses the
_generic_test_punch helper to test all the corner cases across
different extent type transitions.

./check generic/076 generic/232 generic/013 generic/070 generic/269 generic/083 generic/117 generic/068 generic/231 generic/127 generic/091 generic/075 generic/112 generic/263 generic/091 generic/075 generic/256 generic/255 generic/316 generic/300 generic/290;

Note that there is a work in progress on FALLOC_FL_COLLAPSE_RANGE which
touches the same area as this pach set does, so we should figure out
which one should go first and modify the other on top of it.

I was going to push the FALLOC_FL_COLLAPSE_RANGE stuff through
the XFS tree once it was done - perhaps you and Namjae can get
together and work out which order the patch series should go.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com