Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1289955

Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance

Show all headers | View raw

On Fri, Dec 11, 2015 at 2:18 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 12/11/15 14:12, Andy Lutomirski wrote:
>>>
>>> For the newinstance case st_dev should match between the master and the
>>> slave.  Unfortunately this is not the case for a legacy ptmx, as a
>>> stat() on the master descriptor still returns the st_dev, st_rdev, and
>>> st_ino for the ptmx device node.
>>
>> Sure, but I'm not talking about stat.  I'm saying that we could add a
>> new ioctl that works on any ptmx fd (/dev/ptmx or /dev/pts/ptmx) that
>> answers the question "does this ptmx logically belong to the given
>> devpts filesystem".
>>
>> Since it's not stat, we can make it do whatever we want, including
>> following a link to the devpts instance that isn't f_path or f_inode.
>>
>
> Sure.  My thinking, though, was whether or not we can do something that
> works on legacy kernels, and/or is less intrusive than new ioctls.
>
> What is the actual operation we need?

To do the whole shebang at once:

ioctl(ptmx_fd, TIOCWHATEVER, fd_to_devpts_mount);

returns the slave number if fd_to_devpts_mount points to the right
place or an error if not.

ptsname(fd) logically does:

fd_to_devpts_mount = open("/dev/pts", O_RDONLY | O_DIRECTORY);
int n = ioctl(fd, TIOCWHATEVER, fd_to_devpts_mount);
close(fd_to_devpts_mount);
if (n < 0)
  return some error;
return "/dev/pts/" + n;

I think that all kinds of variants are possible.

--Andy

>
>         -hpa
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-11 20:50 +0100
  Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-11 22:00 +0100
    Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-11 22:20 +0100
  Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Al Viro <viro@ZenIV.linux.org.uk> - 2015-12-11 22:10 +0100
    Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-11 22:30 +0100
      Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-11 22:50 +0100
        Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-11 23:20 +0100
          Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-11 23:30 +0100
            Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-11 23:40 +0100
        Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-11 23:20 +0100
          Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-11 23:50 +0100
            Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Jann Horn <jann@thejh.net> - 2015-12-12 00:00 +0100
              Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-12 00:10 +0100
                Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-12 00:20 +0100
                Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-12 00:40 +0100
              Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-12 00:10 +0100
            Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-12 00:00 +0100
            Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Andy Lutomirski <luto@amacapital.net> - 2015-12-12 00:00 +0100
        Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-11 23:20 +0100
  Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Peter Hurley <peter@hurleysoftware.com> - 2015-12-14 20:50 +0100
    Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-14 21:00 +0100
    Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-19 22:30 +0100
      Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-20 05:30 +0100
        Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance "H. Peter Anvin" <hpa@zytor.com> - 2015-12-20 05:40 +0100
          Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-20 11:00 +0100
            Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance ebiederm@xmission.com (Eric W. Biederman) - 2015-12-21 23:20 +0100
              Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance Linus Torvalds <torvalds@linux-foundation.org> - 2015-12-21 23:30 +0100

csiph-web