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Date: Thu, 14 Feb 2002 01:19:33 -0500
To: Uli Martens <um@scientific.de>
Cc: Christoph Rohland <cr@sap.com>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [patch] tmpfs: incr. link-count on directory rename
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From: Jan Harkes <jaharkes@cs.cmu.edu>
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On Thu, Feb 14, 2002 at 02:07:18AM +0100, Uli Martens wrote:
> When I move a directory into another on a tmpfs filesystem, the
> link-count of the new parent directory isn't getting incremented. 
> (which leads to find getting hickup, which eg. lets dpkg produce a
> "bzip2" binary package without binaries, generally not a nice thing) 

Yeah, that optimization actually breaks on so many filesystems
(AFS/Coda/iso9660/msdos/any filesystem which contains more than 65538
subdirectories in a directory/you name it) that they even provided a
flag to disable it (-noleaf), which in my opinion should always be the
default setting.

Another trick on the 'filesystem side' of things is to set the directory
linkcount to 1. Basically find always subtracts 2 and then as long as
the count is not zero, it will stat the entry to see if it's a
directory. So a directory linkcount of 1 will 'underflow' and find will
work correctly for the first 65535 sub-directories.

It's been on my todo list to use this fix in Coda as we have some link
count issues when we're flipping entries between 'faked' symlinks for
mountpoints/conflicts and real directories.

Jan

> @@ -1085,6 +1085,9 @@
>  {
>         int error = -ENOTEMPTY;
>  
> +       if (S_ISDIR(old_dentry->d_inode->i_mode)) {
> +               new_dir->i_nlink++;
> +       }
>         if (shmem_empty(new_dentry)) {
>                 struct inode *inode = new_dentry->d_inode;
>                 if (inode) {

ps. shouldn't the linkcount of the old_dir get decremented too? Also you
should only change the linkcounts when the operation completed
successfully. i.e. something more like,

--- /tmp/shmem.c.orig	Thu Feb 14 01:17:23 2002
+++ /tmp/shmem.c	Thu Feb 14 01:18:25 2002
@@ -1100,6 +1100,10 @@
 		error = 0;
 		old_dentry->d_inode->i_ctime = old_dir->i_ctime = old_dir->i_mtime = CURRENT_TIME;
 	}
+	if (!error && S_ISDIR(old_dentry->d_inode->i_mode)) {
+	    old_dir->i_nlink--;
+	    new_dir->i_nlink++;
+	}
 	return error;
 }
 
-
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