Messages in this thread | | | Date | Tue, 7 Oct 2003 04:11:26 -0400 | From | Jakub Jelinek <> | Subject | Re: POSIX message queues |
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On Tue, Oct 07, 2003 at 09:50:16AM +0200, Peter Waechtler wrote: > > On Sunday, October 05, 2003, at 08:32PM, Jakub Jelinek <jakub@redhat.com> wrote: > > >> Speaking of librt - I should not have to link in pthreads and the > >> run-time overhead associated with it (locking stdio etc.) just so I > >> can use shm_open(). Any chance of fixing this? > > > >That overhead is mostly gone in current glibcs (when using NPTL): > >a) e.g. locking is done unconditionally even when libpthread is not present > > (it is just lock cmpxchgl, inlined) > > > a "lock cmpxchg" is > 100 cycles (according to a recent Linux Journal article > from Paul McKenney: 107ns on 700MHz PentiumIII)
Here is exactly what it does on IA-32/i686+:
# define lll_lock(futex) \ (void) ({ int ignore1, ignore2; \ __asm __volatile ("cmpl $0, %%gs:%P6\n\t" \ "je,pt 0f\n\t" \ "lock\n" \ "0:\tcmpxchgl %1, %2\n\t" \ "jnz _L_mutex_lock_%=\n\t" \ ".subsection 1\n\t" \ ".type _L_mutex_lock_%=,@function\n" \ "_L_mutex_lock_%=:\n\t" \ "leal %2, %%ecx\n\t" \ "call __lll_mutex_lock_wait\n\t" \ "jmp 1f\n\t" \ ".size _L_mutex_lock_%=,.-_L_mutex_lock_%=\n" \ ".previous\n" \ "1:" \ : "=a" (ignore1), "=c" (ignore2), "=m" (futex) \ : "0" (0), "1" (1), "m" (futex), \ "i" (offsetof (tcbhead_t, multiple_threads)) \ : "memory"); })
> you suggested naming the syscall number symbols NR_mq_open instead of > NR_sys_mq_open. In the stub I want to overload some syscalls (e.g. mq_open) > but others not (e.g. mq_timedsend). > > How to deal with that?
The syscall is still mq_open, isn't it? So it should be __NR_mq_open. You simply put the ones where you want to implement them directly in the kernel into syscalls.list (and add sysdeps/generic/mq_*.c stubs; also, mq_{timed,}{receive,send} are cancellation points according to POSIX 2003, so they need to be marked as such). Where you need to do some handling before/after the syscall in userland, you simply write mq_open.c etc. and use INLINE_SYSCALL (or INTERNAL_SYSCALL) in it.
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