Re: udev and devfs - The final word

David Lang
2004-01-05T03:06:14Z

Linus, what Andries is saying is that if you export a directory (say
/home) the process of exporting it somehow uses the /dev device number so
if the server reboots and gets a different device number for the partition
that /home is on the clients won't see it as the same export, breaking the
NFS requirement that a server can be rebooted.

I don't agree with him becouse if the NFS server does include /dev info in
what it shows to the outside world it's already broken.

David Lang

On Sun, 4 Jan 2004, Linus Torvalds wrote:

> Date: Sun, 4 Jan 2004 18:52:56 -0800 (PST)
> From: Linus Torvalds <torvalds@osdl.org>
> To: Andries Brouwer <aebr@win.tue.nl>
> Cc: Rob Love <rml@ximian.com>, rob@landley.net,
> Pascal Schmidt <der.eremit@email.de>, linux-kernel@vger.kernel.org,
> Greg KH <greg@kroah.com>
> Subject: Re: udev and devfs - The final word
>
>
>
> On Sun, 4 Jan 2004, Andries Brouwer wrote:
> >
> > Surprise! Are you leaving POSIX? Or ditching NFS?
> > Or demanding that NFS servers must never reboot?
>
> Ok, Andries, time for you to take a deep breath, and calm down. Because
> your arguments are getting ridiculous in the extreme.
>
> A NFS server is sure as hell not going to export _its_ dynamic /dev to its
> clients. That would be not just stupid, but crazy. Next you tell me that
> you were using devfs and exporting that over NFS.
>
> A NFS server is going to export something _totally_ different than its own
> /dev directory - it needs to be _client_-specific anyway. That's true with
> stable numbers too, btw - ever tried to mount a Solaris /dev on a Linux
> client? No workee.
>
> > A common Unix idiom is testing for the identity
> > of two files by comparing st_ino and st_dev.
> > A broken idiom?
>
> No. It still works. Even if the device numbers change across reboots.
>
> Why? Becuase that _program_ sure as hell isn't running across a reboot.
>
> And again, this is not something we haven't seen before. Have you ever
> looked at the "st_dev" values? Try once - look at what it returns for a
> NFS-mounted filesystem. Ponder. Notice how it already is NOT stable across
> reboots.
>
> In other words, the stuff you're complaining about is all stuff that
> nobody has _ever_ been able to rely on, and that has nothign to do with
> udev or anythign else. It all just shows how 100% right I am for saying
> that you cannot rely on stable numbers.
>
> So I repeat: calm down, and think it through.
>
> Linus
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