[PATCH v20 21/32] xfs: Provide a splice-read stub

[David Howells <dhowells@redhat.com>]

Provide a splice_read stub for XFS.  This does a stat count and a shutdown
check before proceeding.  For buffered I/O, it emits a new trace line and
locks the inode across the call to filemap_splice_read() and adds to the
stats afterwards.  Splicing from DAX files either copies the data into a
buffer (DIO) or splices from the pagecache.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: 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
---
 fs/xfs/xfs_file.c  | 33 ++++++++++++++++++++++++++++++++-
 fs/xfs/xfs_trace.h |  2 +-
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index aede746541f8..bb1ec755a709 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -306,6 +306,37 @@ xfs_file_read_iter(
 	return ret;
 }
 
+STATIC ssize_t
+xfs_file_splice_read(
+	struct file		*in,
+	loff_t			*ppos,
+	struct pipe_inode_info	*pipe,
+	size_t			len,
+	unsigned int		flags)
+{
+	struct inode		*inode = file_inode(in);
+	struct xfs_inode	*ip = XFS_I(inode);
+	struct xfs_mount	*mp = ip->i_mount;
+	ssize_t			ret = 0;
+
+	XFS_STATS_INC(mp, xs_read_calls);
+
+	if (xfs_is_shutdown(mp))
+		return -EIO;
+
+	if (in->f_flags & O_DIRECT)
+		return direct_splice_read(in, ppos, pipe, len, flags);
+
+	trace_xfs_file_splice_read(ip, *ppos, len);
+
+	xfs_ilock(ip, XFS_IOLOCK_SHARED);
+	ret = filemap_splice_read(in, ppos, pipe, len, flags);
+	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
+	if (ret > 0)
+		XFS_STATS_ADD(mp, xs_read_bytes, ret);
+	return ret;
+}
+
 /*
  * Common pre-write limit and setup checks.
  *
@@ -1423,7 +1454,7 @@ const struct file_operations xfs_file_operations = {
 	.llseek		= xfs_file_llseek,
 	.read_iter	= xfs_file_read_iter,
 	.write_iter	= xfs_file_write_iter,
-	.splice_read	= generic_file_splice_read,
+	.splice_read	= xfs_file_splice_read,
 	.splice_write	= iter_file_splice_write,
 	.iopoll		= iocb_bio_iopoll,
 	.unlocked_ioctl	= xfs_file_ioctl,
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index cd4ca5b1fcb0..4db669203149 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -1445,7 +1445,6 @@ DEFINE_RW_EVENT(xfs_file_direct_write);
 DEFINE_RW_EVENT(xfs_file_dax_write);
 DEFINE_RW_EVENT(xfs_reflink_bounce_dio_write);
 
-
 DECLARE_EVENT_CLASS(xfs_imap_class,
 	TP_PROTO(struct xfs_inode *ip, xfs_off_t offset, ssize_t count,
 		 int whichfork, struct xfs_bmbt_irec *irec),
@@ -1535,6 +1534,7 @@ DEFINE_SIMPLE_IO_EVENT(xfs_zero_eof);
 DEFINE_SIMPLE_IO_EVENT(xfs_end_io_direct_write);
 DEFINE_SIMPLE_IO_EVENT(xfs_end_io_direct_write_unwritten);
 DEFINE_SIMPLE_IO_EVENT(xfs_end_io_direct_write_append);
+DEFINE_SIMPLE_IO_EVENT(xfs_file_splice_read);
 
 DECLARE_EVENT_CLASS(xfs_itrunc_class,
 	TP_PROTO(struct xfs_inode *ip, xfs_fsize_t new_size),