linux-kernel - Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE

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Message-ID: <20200612015842.GC23230@ZenIV.linux.org.uk>
Date:   Fri, 12 Jun 2020 02:58:42 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        overlayfs <linux-unionfs@...r.kernel.org>,
        linux-kernel@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...radead.org>,
        Colin Walters <walters@...bum.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        syzbot <syzbot+d6ec23007e951dadf3de@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH v4 1/2] hugetlb: use f_mode & FMODE_HUGETLBFS to identify
 hugetlbfs files

On Thu, Jun 11, 2020 at 05:46:43PM -0700, Mike Kravetz wrote:
> The routine is_file_hugepages() checks f_op == hugetlbfs_file_operations
> to determine if the file resides in hugetlbfs.  This is problematic when
> the file is on a union or overlay.  Instead, define a new file mode
> FMODE_HUGETLBFS which is set when a hugetlbfs file is opened.  The mode
> can easily be copied to other 'files' derived from the original hugetlbfs
> file.
> 
> With this change hugetlbfs_file_operations can be static as it should be.
> 
> There is also a (duplicate) set of shm file operations used for the routine
> is_file_shm_hugepages().  Instead of setting/using special f_op's, just
> propagate the FMODE_HUGETLBFS mode.  This means is_file_shm_hugepages() and
> the duplicate f_ops can be removed.

s/HUGETLBFS/HUGEPAGES/, please.

> While cleaning things up, change the name of is_file_hugepages() to
> is_file_hugetlbfs().  The term hugepages is a bit ambiguous.

Don't, especially since the very next patch adds such on overlayfs...

Incidentally, can a hugetlbfs be a lower layer, while the upper one
is a normal filesystem?  What should happen on copyup?