linux-kernel - Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

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Date:   Tue, 07 Feb 2017 01:24:37 +0900
From:   "J. R. Okajima" <hooanon05g@...il.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Djalal Harouni <tixxdz@...il.com>, Chris Mason <clm@...com>,
        Theodore Tso <tytso@....edu>,
        Josh Triplett <josh@...htriplett.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Andy Lutomirski <luto@...nel.org>,
        Seth Forshee <seth.forshee@...onical.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Dongsu Park <dongsu@...ocode.com>,
        David Herrmann <dh.herrmann@...glemail.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Alban Crequy <alban.crequy@...il.com>,
        Al Viro <viro@...IV.linux.org.uk>,
        "Serge E. Hallyn" <serge@...lyn.com>, Phil Estes <estesp@...il.com>
Subject: Re: [RFC 1/1] shiftfs: uid/gid shifting bind mount

James Bottomley:
> Yes, I know the problem.  However, I believe most current linux
> filesystems no longer guarantee stable, for the lifetime of the file,
> inode numbers.  The usual docker container root is overlayfs, which,
> similarly doesn't support stable inode numbers.  I see the odd
> complaint about docker with overlayfs having unstable inode numbers,
> but none seems to have any serious repercussions.

I think it serious.
Reusing the backend fs' inum is a good approach which Amir wrote.
Based on this, I'd suggest you to support the hardlinks.

bakend_dentry = lookup_one_len()
if (d_inode->i_nlink != 1)
	shiftfs_inode = ilookup();
if (!shiftfs_inode) {
	shiftfs_inode = new_inode();
	shiftfs_inode->i_ino = bakend_dentry->d_inode->i_ino;
}


J. R. Okajima