linux-kernel - RFC: permit link(2) to work across --bind mounts ?

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Message-ID: <47684DBD.6030502@rtr.ca>
Date:	Tue, 18 Dec 2007 17:46:21 -0500
From:	Mark Lord <lkml@....ca>
To:	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: RFC: permit link(2)  to work across --bind mounts ?

Why does link(2) not support hard-linking across bind mount points
of the same underlying filesystem ?

Is it as simple as something like this patch below (minus the printk)?
Not likely, but then I'm not a filesystem guru.

???

--- old/fs/namei.c	2007-12-15 12:33:13.000000000 -0500
+++ linux/fs/namei.c	2007-12-18 17:37:04.000000000 -0500
@@ -2398,8 +2398,11 @@
 	if (error)
 		goto out;
 	error = -EXDEV;
-	if (old_nd.mnt != nd.mnt)
-		goto out_release;
+	if (old_nd.mnt != nd.mnt) {
+		if (old_nd.mnt->mnt_sb != nd.mnt->mnt_sb)
+			goto out_release;
+		printk("sys_linkat: old_nd.mnt != nd.mnt, but sb is the same. Continuing..\n");
+	}
 	new_dentry = lookup_create(&nd, 0);
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
--
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