[PATCH v21 08/30] splice: Make splice from a DAX file use copy_splice_read()

David Howells
2023-05-20T00:01:29Z

Make a read splice from a DAX file go directly to copy_splice_read() to do
the reading as filemap_splice_read() is unlikely to find any pagecache to
splice.

I think this affects only erofs, Ext2, Ext4, fuse and XFS.

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: linux-erofs@lists.ozlabs.org
cc: linux-ext4@vger.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
---

Notes:
ver #21)
- Don't need #ifdef CONFIG_FS_DAX as IS_DAX() is false if !CONFIG_FS_DAX.
- Needs to be in vfs_splice_read(), not generic_file_splice_read().

fs/splice.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 76126b1aafcb..8268248df3a9 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -908,10 +908,10 @@ long vfs_splice_read(struct file *in, loff_t *ppos,
if (unlikely(!in->f_op->splice_read))
return warn_unsupported(in, "read");
/*
- * O_DIRECT doesn't deal with the pagecache, so we allocate a buffer,
- * copy into it and splice that into the pipe.
+ * O_DIRECT and DAX don't deal with the pagecache, so we allocate a
+ * buffer, copy into it and splice that into the pipe.
*/
- if ((in->f_flags & O_DIRECT))
+ if ((in->f_flags & O_DIRECT) || IS_DAX(in->f_mapping->host))
return copy_splice_read(in, ppos, pipe, len, flags);
return in->f_op->splice_read(in, ppos, pipe, len, flags);
}