Re: [PATCH 21/38] union-mount: Support for mounting union mount file systems

[Miklos Szeredi]

On Wed, 4 Aug 2010, Valerie Aurora wrote:
> I went for MS_WHITEOUT and MS_FALLTHRU, and added the checks for the
> ops being non-null.

This bit me.  Mount failing with EINVAL is a big PITA.

Miklos


Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2010-08-05 11:06:56.000000000 +0200
+++ linux-2.6/fs/namespace.c	2010-08-05 11:39:19.000000000 +0200
@@ -1387,6 +1387,7 @@ check_mnt_union(struct path *mntpnt, str
 		return 0;
 
 #ifndef CONFIG_UNION_MOUNT
+	printk(KERN_INFO "union mount: not supported by the kernel\n");
 	return -EINVAL;
 #endif
 	for (p = lower_mnt; p; p = next_mnt(p, lower_mnt)) {
@@ -1396,17 +1397,23 @@ check_mnt_union(struct path *mntpnt, str
 			return -EBUSY;
 	}
 
-	if (!IS_ROOT(mntpnt->dentry))
+	if (!IS_ROOT(mntpnt->dentry)) {
+		printk(KERN_INFO "union mount: not root\n");
 		return -EINVAL;
+	}
 
 	if (mnt_flags & MNT_READONLY)
 		return -EROFS;
 
-	if (!(topmost_mnt->mnt_sb->s_flags & MS_WHITEOUT))
+	if (!(topmost_mnt->mnt_sb->s_flags & MS_WHITEOUT)) {
+		printk(KERN_INFO "union mount: whiteout not supported by fs\n");
 		return -EINVAL;
+	}
 
-	if (!(topmost_mnt->mnt_sb->s_flags & MS_FALLTHRU))
+	if (!(topmost_mnt->mnt_sb->s_flags & MS_FALLTHRU)) {
+		printk(KERN_INFO "union mount: fallthrough not supported by fs\n");
 		return -EINVAL;
+	}
 
 	/* XXX top level mount should only be mounted once */
 
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