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

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Message-ID: <alpine.DEB.1.10.0902081340320.18839@alien.or.mcafeemobile.com>
Date:	Sun, 8 Feb 2009 13:50:11 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Michael Kerrisk <mtk.manpages@...il.com>
cc:	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: Why does timerfd() only support CLOCK_REALTIME and 
 CLOCK_MONOTONIC?

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).



- Davide


---
 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 */
 
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