vfs: no fallback for ->copy_file_range

Now that we have generic_copy_file_range(), remove it as a fallback
case when offloads fail. This puts the responsibility for executing
fallbacks on the filesystems that implement ->copy_file_range and
allows us to add operational validity checks to
generic_copy_file_range().

Rework vfs_copy_file_range() to call a new do_copy_file_range()
helper to execute the copying callout, and move calls to
generic_file_copy_range() into filesystem methods where they
currently return failures.

[Amir] overlayfs is not responsible of executing the fallback.
It is the responsibility of the underlying filesystem.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

1 files changed, 16 insertions, 9 deletions

diff --git a/fs/read_write.c b/fs/read_write.c
index 676b02fae589..b63dcb4e4fe9 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1595,6 +1595,19 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
 }
 EXPORT_SYMBOL(generic_copy_file_range);
 
+static ssize_t do_copy_file_range(struct file *file_in, loff_t pos_in,
+				  struct file *file_out, loff_t pos_out,
+				  size_t len, unsigned int flags)
+{
+	if (file_out->f_op->copy_file_range)
+		return file_out->f_op->copy_file_range(file_in, pos_in,
+						       file_out, pos_out,
+						       len, flags);
+
+	return generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
+				       flags);
+}
+
 /*
  * copy_file_range() differs from regular file read and write in that it
  * specifically allows return partial success.  When it does so is up to
@@ -1655,15 +1668,9 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
 		}
 	}
 
-	if (file_out->f_op->copy_file_range) {
-		ret = file_out->f_op->copy_file_range(file_in, pos_in, file_out,
-						      pos_out, len, flags);
-		if (ret != -EOPNOTSUPP)
-			goto done;
-	}
-
-	ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
-				      flags);
+	ret = do_copy_file_range(file_in, pos_in, file_out, pos_out, len,
+				flags);
+	WARN_ON_ONCE(ret == -EOPNOTSUPP);
 done:
 	if (ret > 0) {
 		fsnotify_access(file_in);