splice: Make splice from a DAX file use copy_splice_read()

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>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
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
Link: https://lore.kernel.org/r/20230522135018.2742245-9-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/splice.c b/fs/splice.c
index 76126b1aafcbe6853b3029f28603be58b9e676bc..8268248df3a908d7e617c945904f0e15a9a05acc 100644 (file)
--- 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);
 }