Re: [PATCH v4] loop: fix no-unmap write-zeroes request behavior

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On 10/30/19 9:29 PM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> 
> Currently, if the loop device receives a WRITE_ZEROES request, it asks
> the underlying filesystem to punch out the range.  This behavior is
> correct if unmapping is allowed.  However, a NOUNMAP request means that
> the caller doesn't want us to free the storage backing the range, so
> punching out the range is incorrect behavior.
> 
> To satisfy a NOUNMAP | WRITE_ZEROES request, loop should ask the
> underlying filesystem to FALLOC_FL_ZERO_RANGE, which is (according to
> the fallocate documentation) required to ensure that the entire range is
> backed by real storage, which suffices for our purposes.

Applied, thanks Darrick.

-- 
Jens Axboe




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