xfs: Provide a splice-read wrapper

xfs: Provide a splice-read wrapper

Provide a splice_read wrapper for XFS.  This does a stat count and a
shutdown check before proceeding, then emits a new trace line and locks the
inode across the call to filemap_splice_read() and adds to the stats
afterwards.  Splicing from direct I/O or DAX is handled by the caller.

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Darrick J. Wong <djwong@kernel.org>
cc: linux-xfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-25-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>