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 <dhowells@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner <brauner@kernel.org>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-8-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/splice.c b/fs/splice.c
index fe3309f..76126b1 100644 (file)
--- a/fs/splice.c
+++ b/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);