linux-kernel - Re: regression, bisected: openpty fails from 3.7 onwards without devpts

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Message-ID: <20130110162907.GB26279@breakpoint.cc>
Date:	Thu, 10 Jan 2013 17:29:07 +0100
From:	Florian Westphal <fw@...len.de>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	Florian Westphal <fw@...len.de>, linux-kernel@...r.kernel.org,
	gaowanlong@...fujitsu.com, gregkh@...uxfoundation.org,
	frank@...htenheld.de
Subject: Re: regression, bisected: openpty fails from 3.7 onwards without
 devpts

Alan Cox <alan@...ux.intel.com> wrote:
> On Thu, 10 Jan 2013 15:46:26 +0100
> Florian Westphal <fw@...len.de> wrote:
> > Frank Lichtenheld discovered that openpty() doesn't work anymore when
> > /dev/pts is not present.
> > 
> > We bisected this down to
> > 
> > commit bbb63c514a3464342967237a51a21ea8f61ab951
> > Author: Wanlong Gao <gaowanlong@...fujitsu.com>
> > Subject: drivers:tty:fix up ENOIOCTLCMD error handling

[..]

> > #include <stdio.h>
> > #include <pty.h>
> > int main(void) {
> >  int pty_fd, tty_fd;
> >  if (openpty(&pty_fd, &tty_fd, NULL, NULL, NULL) != 0) {
> >   perror("openpty");
> >   return 1;
> >  }
> > return 0;
> > }
> > ----
> > [ compile with cc -lutil pty.c -o pty ]
> > 
> > If devpts is available or above commit reverted openpty works again.
> 
> The commit is fairly general - what we need to do here is to figure out
> which specific thing trips up openpty so we can put the error on that
> back as it was (or find a better way) so it still works.
> 
> Can you attach an strace of the working/failing cases without /dev/pts 

Sure, attached.  /dev/pts is not present.
Both traces are from the same machine, with same kernel version (except
above commit reverted).

View attachment "openpty.ok.trace.txt" of type "text/plain" (8187 bytes)

View attachment "openpty.fail.trace.txt" of type "text/plain" (3650 bytes)