linux-kernel - Re: [GIT PULL] xen: xenfs fixes for 4.9-rc2

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Message-ID: <CA+55aFz52bo7HJLNoorBW20yrLY7svVJu+BHS3KYA0Zy_kPfgQ@mail.gmail.com>
Date:   Mon, 24 Oct 2016 20:28:25 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Vrabel <dvrabel@...tab.net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [GIT PULL] xen: xenfs fixes for 4.9-rc2

On Mon, Oct 24, 2016 at 9:37 AM, David Vrabel <dvrabel@...tab.net> wrote:
>
> I think the changes are trivial and uncontroversial.

Hmm. Sadly, they are also buggy.

This:

                if (files->mode & S_IFLNK) {

is simply wrong. The correct test for S_IFLNK is to do

                if ((files->mode & S_IFMT) == S_IFLNK) {

and quite frankly, the right model is almost certainly to just do a
switch-statement that does something like

                switch (files->mode & S_IFMT) {
                case S_IFLNK:
                        ...
                case S_IFREG:
                case 0:
                        ....
                default:
                        ..error..

because maybe somebody wants to add other cases later (and even if
not, it's just wrong to randomly change any other mode into S_IFREG).

And while I could easily do an evil merge and fix that part up, I
really don't want to do things like that. So I'm not going to pull
this.

               Linus