Re: [PATCH v4 5/6] xfs: create delalloc bmapi wrapper for full extent allocation

[Christoph Hellwig <hch@infradead.org>]

On Fri, Feb 01, 2019 at 09:32:55AM -0500, Brian Foster wrote:
> The writeback delalloc conversion code is racy with respect to
> changes in the currently cached file mapping. This stems from the
> fact that the bmapi allocation code requires a file range to
> allocate and the writeback conversion code assumes the range of the
> currently cached mapping is still valid with respect to the fork. It
> may not be valid, however, because the ilock is cycled (potentially
> multiple times) between the time the cached mapping was populated
> and the delalloc conversion occurs.
> 
> To facilitate a solution to this problem, create a new
> xfs_bmapi_delalloc() wrapper to xfs_bmapi_write() that takes a file
> (FSB) offset and attempts to allocate whatever delalloc extent backs
> the offset. Use a new bmapi flag to cause xfs_bmapi_write() to set
> the range based on the extent backing the bno parameter unless bno
> lands in a hole. If bno does land in a hole, fall back to the
> current behavior (which may result in an error or quietly skipping
> holes in the specified range depending on other parameters). This
> patch does not change behavior.
> 
> [hch: Rename helper function and tweak interface.]
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good.  Feel free to drop the [hch: ] note and replace my
signoff for that with a:

Reviewed-by: Christoph Hellwig <hch@lst.de>

for the whole patch.