linux-kernel - Re: [PATCH v2] ovl: provide real_file() and overlayfs get_unmapped

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Message-ID: <20200611021710.GA23230@ZenIV.linux.org.uk>
Date:   Thu, 11 Jun 2020 03:17:10 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        kbuild test robot <lkp@...el.com>, kbuild-all@...ts.01.org,
        Colin Walters <walters@...bum.org>,
        syzbot <syzbot+d6ec23007e951dadf3de@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        overlayfs <linux-unionfs@...r.kernel.org>
Subject: Re: [PATCH v2] ovl: provide real_file() and overlayfs
 get_unmapped_area()

On Wed, Jun 10, 2020 at 06:36:16PM -0700, Matthew Wilcox wrote:

> 	while (file->f_mode & FMODE_OVL_UPPER)
> 		file = file->private_data;
> 	return file;
> 
> Or are you proposing that overlayfs copy FMODE_HUGEPAGES from the
> underlying fs to the overlaying fs?

The latter - that way nobody outside of overlayfs needs to know what
its ->private_data points to, for one thing.  And it's cheaper that
way, obviously.