GIT: unionfs2-2.6.27.y: Unionfs: fix readonly nfs2/3 permission handling

[Erez Zadok]

commit f9d2daab7e9b64792b3f095d52dce5d2833e3a3d
Author: Erez Zadok <ezk at cs.sunysb.edu>
Date:   Tue Sep 22 17:35:15 2009 -0400

    Unionfs: fix readonly nfs2/3 permission handling
    
    In unionfs_permission: NFSv2/3 return EACCES on readonly-exported, locally
    readonly-mounted file systems, instead of EROFS like other file systems do.
    So we have no choice here but to intercept this and ignore it for NFS
    branches marked readonly.  Specifically, we avoid using NFS's own "broken"
    ->permission method, and rely on generic_permission() to do basic checking
    for us.
    
    Signed-off-by: Erez Zadok <ezk at cs.sunysb.edu>

diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index 7c17093..7e86273 100644
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -843,6 +843,20 @@ static int unionfs_permission(struct inode *inode, int mask)
 		}
 
 		/*
+		 * NFS HACK: NFSv2/3 return EACCES on readonly-exported,
+		 * locally readonly-mounted file systems, instead of EROFS
+		 * like other file systems do.  So we have no choice here
+		 * but to intercept this and ignore it for NFS branches
+		 * marked readonly.  Specifically, we avoid using NFS's own
+		 * "broken" ->permission method, and rely on
+		 * generic_permission() to do basic checking for us.
+		 */
+		if (err && err == -EACCES &&
+		    is_robranch_super(inode->i_sb, bindex) &&
+		    lower_inode->i_sb->s_magic == NFS_SUPER_MAGIC)
+			err = generic_permission(lower_inode, mask, NULL);
+
+		/*
 		 * The permissions are an intersection of the overall directory
 		 * permissions, so we fail if one fails.
 		 */