On Sat, Oct 12, 2019 at 01:46:54PM +0200, Michael Kerrisk (man-pages) wrote:
On 10/12/19 9:48 AM, Christian Brauner wrote:
On Sat, Oct 12, 2019 at 08:53:34AM +0200, Michael Kerrisk (man-pages) wrote:
Hello Aleksa,
On Sat, 12 Oct 2019 at 00:12, Aleksa Sarai cyphar@cyphar.com wrote:
On 2019-10-11, Michael Kerrisk mtk.manpages@gmail.com wrote:
Why CLONE3_CLEAR_SIGHAND rather than just CLONE_CLEAR_SIGHAND?
I don't care much how we name this apart from the "_CLEAR_SIGHAND" suffix. But see for a little rationale below.
There are no more flag bits left for the classic clone()/clone2() (the last one was used up by CLONE_PIDFD) -- thus this flag is clone3()-only.
Yes, I understand that. But, I'm not sure that the "3" in the prefix is necessary. "CLONE_" still seems better to me.
Consider this: sometime in the near future we will probably have time namespaces. The new flag for those namespaces will only be usable with clone3(). It should NOT be called CLONE3_NEWTIME, but rather CLONE_NEWTIME (or similar), because that same flag will presumably also be used in other APIs such as unshare() and setns(). (Hmm -- I
There are some noteable differences though. CLONE_NEWTIME takes the CSIGNAL bit which is in the range of a 32bit integer and thus useable by unshare() too. The same does not hold for CLONE{3}_CLEAR_SIGHAND. You can't pass it to unshare(). unshare() also just deals with namespace-relevant stuff so CLONE{3}_CLEAR_SIGHAND doesn't make much sense there.
Sure, but going forward there's very likely to be more CLONE flags for whatever reason, and some will be usable just in clone3() while others will be more widely used (in other APIs such as unshare() and setns()). Using two different prefixes for these flags (CLONE_/CLONE3_) would be just confusing. AFAICS, the CLONE3_
I do agree with that part. And as I said in my previous mail, I don't care about the prefix.
prefix really provides no advantage, but does have the potential to cause confusion down the track for the aforementioned reasons. (Furthermore... Shudder! What if there's a clone4() one day. I know you might say: "won't happen, we got things right this time", but API history suggests that "right" now not infrequently becomes "oops" later.) I do recommend CLONE_ for all the flags...
I do love your trust in our ability to design syscalls (//Cc Aleksa ;)). :)
wonder if we are going to need a new unshare2() or some such...)
We still have one 32bit bit left (CLONE_DETACHED) which we can't reuse with clone()/clone2() but we can reuse with clone3(). We can simply earmark it for namespace-related stuff and thus still have one bit left for unshare() before we have to go for unshare2() (If we have to go there at all since I'm not sure how much more namespaces we can come up with.).
I'm sure there'll be more namespaces...
Let's hope not. :) Anyway, no real reason to do unshare2() any time soon. :)
Christian