overlayfs: Implement splice-read

Implement splice-read for overlayfs by passing the request down a layer
rather than going through generic_file_splice_read() which is going to be
changed to assume that ->read_folio() is present on buffered files.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Christian Brauner <brauner@kernel.org>
cc: Christoph Hellwig <hch@lst.de>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: John Hubbard <jhubbard@nvidia.com>
cc: David Hildenbrand <david@redhat.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Miklos Szeredi <miklos@szeredi.hu>
cc: Amir Goldstein <amir73il@gmail.com>
cc: linux-unionfs@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/20230522135018.2742245-11-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 7c04f033aadd75d36d078d3ca1d1669867605a2b..86197882ff35128424dd0ddd2d26058d68100847 100644 (file)
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -419,6 +419,27 @@ out_unlock:
        return ret;
 }
 
+static ssize_t ovl_splice_read(struct file *in, loff_t *ppos,
+                              struct pipe_inode_info *pipe, size_t len,
+                              unsigned int flags)
+{
+       const struct cred *old_cred;
+       struct fd real;
+       ssize_t ret;
+
+       ret = ovl_real_fdget(in, &real);
+       if (ret)
+               return ret;
+
+       old_cred = ovl_override_creds(file_inode(in)->i_sb);
+       ret = vfs_splice_read(real.file, ppos, pipe, len, flags);
+       revert_creds(old_cred);
+       ovl_file_accessed(in);
+
+       fdput(real);
+       return ret;
+}
+
 /*
  * Calling iter_file_splice_write() directly from overlay's f_op may deadlock
  * due to lock order inversion between pipe->mutex in iter_file_splice_write()
@@ -695,7 +716,7 @@ const struct file_operations ovl_file_operations = {
        .fallocate      = ovl_fallocate,
        .fadvise        = ovl_fadvise,
        .flush          = ovl_flush,
-       .splice_read    = generic_file_splice_read,
+       .splice_read    = ovl_splice_read,
        .splice_write   = ovl_splice_write,
 
        .copy_file_range        = ovl_copy_file_range,