Re: [PATCH] ipc/msg: add msgsnd_timed and msgrcv_timed syscall for system V message queue
From: Arnd Bergmann <arnd@kernel.org>
Date: 2021-02-27 12:30:43
Also in:
linux-api, linux-arch, linux-arm-kernel, lkml
On Sat, Feb 27, 2021 at 7:52 AM Eric Gao [off-list ref] wrote:
sometimes, we need the msgsnd or msgrcv syscall can return after a limited time, so that the business thread do not be blocked here all the time. In this case, I add the msgsnd_timed and msgrcv_timed syscall that with time parameter, which has a unit of ms. Signed-off-by: Eric Gao <redacted>
I have no opinion on whether we want or need this, but I'll have a look at the implementation, to see if the ABI makes sense.
quoted hunk ↗ jump to hunk
index 8fd8c17..42b7db5 100644--- a/arch/mips/kernel/syscalls/syscall_n32.tbl +++ b/arch/mips/kernel/syscalls/syscall_n32.tbl@@ -381,3 +381,5 @@ 440 n32 process_madvise sys_process_madvise 441 n32 epoll_pwait2 compat_sys_epoll_pwait2 442 n32 mount_setattr sys_mount_setattr +443 n32 msgrcv_timed sys_msgrcv_timed +444 n32 msgsnd_timed sys_msgsnd_timeddiff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl index 090d29c..0f1f6ee 100644 --- a/arch/mips/kernel/syscalls/syscall_o32.tbl +++ b/arch/mips/kernel/syscalls/syscall_o32.tbl@@ -430,3 +430,5 @@ 440 o32 process_madvise sys_process_madvise 441 o32 epoll_pwait2 sys_epoll_pwait2 compat_sys_epoll_pwait2 442 o32 mount_setattr sys_mount_setattr +443 o32 msgrcv_timed sys_msgrcv_timed +444 o32 msgsnd_timed sys_msgsnd_timed
I think mips n32 and o32 both need to use the compat version when running on a 64-bit kernel, while your patch makes them use the native version.
quoted hunk ↗ jump to hunk
@@ -905,7 +906,15 @@ static long do_msgsnd(int msqid, long mtype, void __user *mtext, ipc_unlock_object(&msq->q_perm); rcu_read_unlock(); - schedule(); + + /* sometimes, we need msgsnd syscall return after a given time */ + if (timeoutms <= 0) { + schedule(); + } else { + timeoutms = schedule_timeout(timeoutms); + if (timeoutms == 0) + timeoutflag = true; + }
I wonder if this should be schedule_timeout_interruptible() or at least schedule_timeout_killable() instead of schedule_timeout(). If it should, this should probably be done as a separate change.
+COMPAT_SYSCALL_DEFINE5(msgsnd_timed, int, msqid, compat_uptr_t, msgp,
+ compat_ssize_t, msgsz, int, msgflg, compat_long_t, timeoutms)
+{
+ struct compat_msgbuf __user *up = compat_ptr(msgp);
+ compat_long_t mtype;
+
+ timeoutms = (timeoutms + 9) / 10;
+
+ if (get_user(mtype, &up->mtype))
+ return -EFAULT;
+
+ return do_msgsnd(msqid, mtype, up->mtext, (ssize_t)msgsz, msgflg, (long)timeoutms);
+}
My preference would be to simplify both the timed and non-timed version by
moving the get_user() into do_msgsnd() and using in_compat_task() to pick
the right type. Same for the receive side of course. If you do this,
watch out for
x32 support, which uses the 64-bit version.
Arnd