On Friday 27 April 2012 01:07:42 Rich Felker wrote: > On Fri, Apr 27, 2012 at 12:58:33AM -0400, Mike Frysinger wrote: > > On Thursday 26 April 2012 23:08:36 Rich Felker wrote: > > > On Thu, Apr 26, 2012 at 10:50:57PM -0400, Mike Frysinger wrote: > > > > > This patch adds a test for __UCLIBC_VFORK_USES_CLONE__ feature > > > > > definition which an architecture may define if vfork is implemented > > > > > using clone. > > > > > > > > err, if your kernel arch doesn't have vfork, why is it defining > > > > __NR_vfork ? i.e. the uClibc logic should not require > > > > __UCLIBC_VFORK_USES_CLONE__. it can deduce that itself by saying "if > > > > !vfork && !fork && clone". > > > > > > I don't think !fork belongs in the test. Implementing vfork with clone > > > is better than implementing it as just a duplicate of fork. But I'm > > > not sure how having macros for this can be useful at all since, > > > whatever syscall is used to implement vfork, it has to be written in > > > asm unless it's just a duplicate of fork. > > > > if we've got a C-callable clone(), i think we can implement a C vfork() > > on top of that. it'd be a tail call, so the semantics of parallel stack > > usage should be the same. > > > > i know ia64 implements vfork() with clone(), but it does it in asm, so > > that doesn't make my case :p. > > The standard libc wrapper API for the clone syscall does not return > twice. It calls a function (function pointer argument) in the new > thread/process. This makes it useless for implementing vfork.
err, yeah, i was thinking it only took flags > theory it could be designed to return in the child as well if the > called function returns, but I think the usual behavior is for it to > call SYS_exit (exit thread) in that case.. probably could be done with a bit of care in C and writing a dedicated clone func, but i don't think this would really gain anything, and would be hard to write in a way that didn't just end up bloating. since every arch has implemented vfork() and clone() in assembly anyways, requiring someone who doesn't have a __NR_vfork isn't anything new. as mentioned, ia64 already does this, and looking a little closer, seems that mips does as well. -mike
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