Re: Why does timerfd() only support CLOCK_REALTIME and CLOCK_MONOTONIC?

Michael Kerrisk
2009-02-08T22:03:59Z

On Mon, Feb 9, 2009 at 10:50 AM, Davide Libenzi <davidel@xmailserver.org> wrote:
> On Mon, 9 Feb 2009, Michael Kerrisk wrote:
>
>> > @@ -186,12 +187,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clo
>> > BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
>> > BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
>> >
>> > - if (flags & ~(TFD_CLOEXEC | TFD_NONBLOCK))
>> > + if ((flags & ~TFD_FLAGS_SET) ||
>> > + invalid_clockid(clockid))
>> > return -EINVAL;
>>
>> Oh! Does this mean that in 2.6.2[789] it wasn't possible to use
>> TFD_TIMER_ABSTIME?
>
> No, sorry, my fault. Patch is wrong. In "create" ATM we accept only
> FCNTL-like flags. In "settime" we get TFD_TIMER_ABSTIME (that needs a
> check too for EINVAL).

That last piece should be a separate patch, that also gets pushed back
into -stable. Do you agree?

M

> ---
> fs/timerfd.c | 13 ++++++-------
> include/linux/posix-timers.h | 1 +
> include/linux/timerfd.h | 15 ++++++++++++---
> kernel/posix-timers.c | 2 +-
> 4 files changed, 20 insertions(+), 11 deletions(-)
>
> Index: linux-2.6.mod/fs/timerfd.c
> ===================================================================
> --- linux-2.6.mod.orig/fs/timerfd.c 2009-02-08 12:32:25.000000000 -0800
> +++ linux-2.6.mod/fs/timerfd.c 2009-02-08 13:44:47.000000000 -0800
> @@ -18,6 +18,7 @@
> #include <linux/spinlock.h>
> #include <linux/time.h>
> #include <linux/hrtimer.h>
> +#include <linux/posix-timers.h>
> #include <linux/anon_inodes.h>
> #include <linux/timerfd.h>
> #include <linux/syscalls.h>
> @@ -186,12 +187,9 @@ SYSCALL_DEFINE2(timerfd_create, int, clo
> BUILD_BUG_ON(TFD_CLOEXEC != O_CLOEXEC);
> BUILD_BUG_ON(TFD_NONBLOCK != O_NONBLOCK);
>
> - if (flags & ~(TFD_CLOEXEC | TFD_NONBLOCK))
> + if ((flags & ~TFD_CREATE_FLAGS) ||
> + invalid_clockid(clockid))
> return -EINVAL;
> - if (clockid != CLOCK_MONOTONIC &&
> - clockid != CLOCK_REALTIME)
> - return -EINVAL;
> -
> ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
> if (!ctx)
> return -ENOMEM;
> @@ -201,7 +199,7 @@ SYSCALL_DEFINE2(timerfd_create, int, clo
> hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
>
> ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
> - flags & (O_CLOEXEC | O_NONBLOCK));
> + flags & TFD_SHARED_FCNTL_FLAGS);
> if (ufd < 0)
> kfree(ctx);
>
> @@ -219,7 +217,8 @@ SYSCALL_DEFINE4(timerfd_settime, int, uf
> if (copy_from_user(&ktmr, utmr, sizeof(ktmr)))
> return -EFAULT;
>
> - if (!timespec_valid(&ktmr.it_value) ||
> + if ((flags & ~TFD_SETTIME_FLAGS) ||
> + !timespec_valid(&ktmr.it_value) ||
> !timespec_valid(&ktmr.it_interval))
> return -EINVAL;
>
> Index: linux-2.6.mod/include/linux/posix-timers.h
> ===================================================================
> --- linux-2.6.mod.orig/include/linux/posix-timers.h 2009-02-08 12:32:25.000000000 -0800
> +++ linux-2.6.mod/include/linux/posix-timers.h 2009-02-08 12:33:12.000000000 -0800
> @@ -84,6 +84,7 @@ struct k_clock {
> struct itimerspec * cur_setting);
> };
>
> +int invalid_clockid(const clockid_t which_clock);
> void register_posix_clock(const clockid_t clock_id, struct k_clock *new_clock);
>
> /* error handlers for timer_create, nanosleep and settime */
> Index: linux-2.6.mod/kernel/posix-timers.c
> ===================================================================
> --- linux-2.6.mod.orig/kernel/posix-timers.c 2009-02-08 12:32:25.000000000 -0800
> +++ linux-2.6.mod/kernel/posix-timers.c 2009-02-08 12:32:57.000000000 -0800
> @@ -205,7 +205,7 @@ static int no_timer_create(struct k_itim
> /*
> * Return nonzero if we know a priori this clockid_t value is bogus.
> */
> -static inline int invalid_clockid(const clockid_t which_clock)
> +int invalid_clockid(const clockid_t which_clock)
> {
> if (which_clock < 0) /* CPU clock, posix_cpu_* will check it */
> return 0;
> Index: linux-2.6.mod/include/linux/timerfd.h
> ===================================================================
> --- linux-2.6.mod.orig/include/linux/timerfd.h 2009-02-08 12:34:25.000000000 -0800
> +++ linux-2.6.mod/include/linux/timerfd.h 2009-02-08 13:47:57.000000000 -0800
> @@ -11,13 +11,22 @@
> /* For O_CLOEXEC and O_NONBLOCK */
> #include <linux/fcntl.h>
>
> -/* Flags for timerfd_settime. */
> +/*
> + * CAREFUL: Check include/asm-generic/fcntl.h when defining
> + * new flags, since they might collide with O_* ones. We want
> + * to re-use O_* flags that couldn't possibly have a meaning
> + * from eventfd, in order to leave a free define-space for
> + * shared O_* flags.
> + */
> #define TFD_TIMER_ABSTIME (1 << 0)
> -
> -/* Flags for timerfd_create. */
> #define TFD_CLOEXEC O_CLOEXEC
> #define TFD_NONBLOCK O_NONBLOCK
>
> +#define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK)
> +#define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS
> +#define TFD_SETTIME_FLAGS TFD_TIMER_ABSTIME
> +#define TFD_FLAGS_SET (TFD_SHARED_FCNTL_FLAGS | TFD_TIMER_ABSTIME)
> +
>
> #endif /* _LINUX_TIMERFD_H */