linux-kernel - Re: [PATCH] fs: ext4: inode->i

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Message-ID: <20170629183053.GA4178@fieldses.org>
Date:   Thu, 29 Jun 2017 14:30:53 -0400
From:   "J. Bruce Fields" <bfields@...ldses.org>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     William Koh <kkc6196@...com>, Andreas Dilger <adilger@...ger.ca>,
        Theodore Ts'o <tytso@....edu>,
        linux-ext4 <linux-ext4@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        xfs <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH] fs: ext4: inode->i_generation not assigned 0.

On Thu, Jun 29, 2017 at 10:25:28AM -0700, Darrick J. Wong wrote:
> Was there ever a version of NFS (or more generally callers of the
> exportfs code) that couldn't deal with i_generation in the file handle,
> and therefore we invented this generation hack to work around the loss
> of the generation information?
> 
> There's a comment in xfs_fs_encode_fh about not supporting 64bit inodes
> with subtree_check (which seems to require one ino/gen pair for the file
> and a second pair for the file's parent) on NFSv2 because v2 doesn't
> provide enough space for all the file handle information, but that's the
> furthest I got with lazy-mining the git history. :)

There's a comment in fs/ext4/super.c:ext4_nfs_get_inode

	* Currently we don't know the generation for parent directory, so
	* a generation of 0 means "accept any"

But I don't see that used.

It was used once upon a time; I see it actually used in old 2.5 code in
nfsd_get_dentry.  Hm.

--b.