[lkml]   [2020]   [Feb]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Time Namespaces: CLONE_NEWTIME and clone3()?
On Mon, Feb 17, 2020 at 03:20:55PM +0100, Michael Kerrisk wrote:
> Hello Dmitry, Andrei,
> Is the CLONE_NEWTIME flag intended to be usable with clone3()? The
> mail quoted below implies (in my reading) that this should be possible
> once clone3() is available, which it is by now. (See also [1].)
> If the answer is yes, CLONE_NEWTIME should be usable with clone3(),
> then I have a bug report and a question.
> I successfully used CLONE_NEWTIME with unshare(). But if I try to use
> CLONE_NEWSIGNAL with clone3(), it errors out with EINVAL, because of


> the following check in clone3_args_valid():
> /*
> * - make the CLONE_DETACHED bit reuseable for clone3
> * - make the CSIGNAL bits reuseable for clone3
> */
> if (kargs->flags & (CLONE_DETACHED | CSIGNAL))
> return false;
> The problem is that CLONE_NEWTIME matches one of the bits in the
> CSIGNAL mask. If the intention is to allow CLONE_NEWTIME with
> clone3(), then either the bit needs to be redefined, or the error
> checking in clone3_args_valid() needs to be reworked.

If this is intended to be useable with clone3() the check should be
adapted to allow for CLONE_NEWTIME. (I asked about this a while ago I
But below rather sounds like it should simply be an unshare() flag. The
code seems to set frozen_offsets to true right after copy_namespaces()
in timens_on_fork(new_ns, tsk) and so the offsets can't be changed
anymore unless I'm reading this wrong.
Alternatives seem to either make timens_offsets writable once after fork
and before exec, I guess - though that's probably not going to work
with the vdso judging from timens_on_fork().

The other alternative is that Andrei and Dmitry send me a patch to
enable CLONE_NEWTIME with clone3() by exposing struct timens_offsets (or
a version of it) in the uapi and extend struct clone_args to include a
pointer to a struct timens_offset that is _only_ set when CLONE_NEWTIME
is set.
Though the unshare() way sounds way less invasive simpler.


 \ /
  Last update: 2020-02-17 15:59    [W:0.081 / U:25.108 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site