linux-kernel - Re: Why does timerfd() only support CLOCK_REALTIME and CLOCK

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Message-ID: <cfd18e0f0902081353t70f9e107g28f8003f356f84db@mail.gmail.com>
Date:	Mon, 9 Feb 2009 10:53:03 +1300
From:	Michael Kerrisk <mtk.manpages@...glemail.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, stable@...nel.org
Subject: Re: Why does timerfd() only support CLOCK_REALTIME and 
	CLOCK_MONOTONIC?

On Mon, Feb 9, 2009 at 10:50 AM, Davide Libenzi <davidel@...ilserver.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 */
>
>



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git
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