splice: Make splice from an O_DIRECT fd use copy_splice_read()

Make a read splice from a file descriptor that's open O_DIRECT use
copy_splice_read() to do the reading as filemap_splice_read() is unlikely
to find any pagecache to splice.

Signed-off-by: David Howells <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Christian Brauner <[email protected]>
cc: Al Viro <[email protected]>
cc: Jens Axboe <[email protected]>
cc: [email protected]
cc: [email protected]
cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: dhowells

fs/splice.c

@@ -907,6 +907,12 @@ 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.
+	 */
+	if ((in->f_flags & O_DIRECT))
+		return copy_splice_read(in, ppos, pipe, len, flags);
 	return in->f_op->splice_read(in, ppos, pipe, len, flags);
 }
 EXPORT_SYMBOL_GPL(vfs_splice_read);