GNU bug report logs - #22053
'call-with-container' fails when CONFIG_DEVPTS_MULTIPLE_INSTANCES is not set

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Message #20 received at 22053 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Efraim Flashner <efraim <at> flashner.co.il>
Cc: David Thompson <dthompson2 <at> worcester.edu>, 22053 <at> debbugs.gnu.org
Subject: Re: bug#22053: silent failure on guix environment foo --container
Date: Mon, 30 Nov 2015 13:51:12 +0100

Efraim Flashner <efraim <at> flashner.co.il> skribis:

> On Mon, 30 Nov 2015 13:22:34 +0100
> ludo <at> gnu.org (Ludovic Courtès) wrote:
>
>> Efraim Flashner <efraim <at> flashner.co.il> skribis:
>> 
>> > On Sun, 29 Nov 2015 22:20:33 +0100
>> > ludo <at> gnu.org (Ludovic Courtès) wrote:
>> >  
>> >> Efraim Flashner <efraim <at> flashner.co.il> skribis:
>> >> 
>> >>  [...]  
>> >> 
>> >> The failure is:
>> >> 
>> >> --8<---------------cut here---------------start------------->8---
>> >> 21228 mount("none", "/tmp/guix-directory.5sVcGc//dev/pts", "devpts", MS_NOSUID|MS_NOEXEC, "newinstance,ptmxmode=0666,mode=6"...) = -1 EPERM (Operation not permitted)
>> >> 21228 exit_group(1)                     = ?
>> >> --8<---------------cut here---------------end--------------->8---
>> >> 
>> >> The problem may be that the kernel does not support
>> >> CONFIG_DEVPTS_MULTIPLE_INSTANCES.  Could you check that in
>> >> /proc/config.gz or similar?  
>> >
>> > # CONFIG_DEVPTS_MULTIPLE_INSTANCES is not set  
>> 
>> QED.  :-)  However, the daemon needs it too.  Don’t you have problems
>> with guix-daemon as well, when building things locally on that machine?
>> 
>> Ludo’.
>
> Not at all, I've been building things all day.

I’ve realized that the daemon has a fallback case for this situation, in
libstore/build.cc:

--8<---------------cut here---------------start------------->8---
  /* Mount a new devpts on /dev/pts.  Note that this
     requires the kernel to be compiled with
     CONFIG_DEVPTS_MULTIPLE_INSTANCES=y (which is the case
     if /dev/ptx/ptmx exists). */
  if (pathExists("/dev/pts/ptmx") &&
      !pathExists(chrootRootDir + "/dev/ptmx")
      && dirsInChroot.find("/dev/pts") == dirsInChroot.end())
  {
      if (mount("none", (chrootRootDir + "/dev/pts").c_str(), "devpts", 0, "newinstance,mode=0620") == -1)
          throw SysError("mounting /dev/pts");
      createSymlink("/dev/pts/ptmx", chrootRootDir + "/dev/ptmx");

      /* Make sure /dev/pts/ptmx is world-writable.  With some
         Linux versions, it is created with permissions 0.  */
      chmod_(chrootRootDir + "/dev/pts/ptmx", 0666);
  }
--8<---------------cut here---------------end--------------->8---

David, should we do something similar?

Thanks,
Ludo’.

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