Davi Arnaut a écrit :
Eric Dumazet wrote:
Davi Arnaut a écrit :
Asynchronously wait for FUTEX_WAKE operation on a futex if it still contains
a given value. There can be only one futex wait per file descriptor. However,
it can be rearmed (possibly at a different address) anytime.
The pollable futex approach is far superior (send and receive events from
userspace or kernel) to eventfd and fixes (supercedes) FUTEX_FD at the same time.
Building block for pollable semaphores and user-defined events.
Signed-off-by: Davi E. M. Arnaut <[email protected]>
---
fs/pollfs/Makefile | 1
fs/pollfs/futex.c | 154 +++++++++++++++++++++++++++++++++++++++++++++++++++++
init/Kconfig | 7 ++
3 files changed, 162 insertions(+)
Index: linux-2.6/fs/pollfs/Makefile
===================================================================
--- linux-2.6.orig/fs/pollfs/Makefile
+++ linux-2.6/fs/pollfs/Makefile
@@ -3,3 +3,4 @@ pollfs-y := file.o
pollfs-$(CONFIG_POLLFS_SIGNAL) += signal.o
pollfs-$(CONFIG_POLLFS_TIMER) += timer.o
+pollfs-$(CONFIG_POLLFS_FUTEX) += futex.o
Index: linux-2.6/fs/pollfs/futex.c
===================================================================
--- /dev/null
+++ linux-2.6/fs/pollfs/futex.c
@@ -0,0 +1,154 @@
+/*
+ * pollable futex
+ *
+ * Copyright (C) 2007 Davi E. M. Arnaut
+ *
+ * Licensed under the GNU GPL. See the file COPYING for details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/pollfs_fs.h>
+#include <linux/futex.h>
+
+struct futex_event {
+ union {
+ void __user *addr;
+ u64 padding;
+ };
+ int val;
+};
Hum... Here we might have a problem with 64 bit futexes, or private futexes
So I believe this interface is not well defined and not expandable: in case of
future additions to futexes, an old application compiled with an old pollable
futex_event type might fail.
Hmm, how about:
struct futex_event {
union {
void __user *addr;
u64 padding;
};
union {
int val;
s64 val64;
};
/* whatever room is necessary for future improvements */
};
I haven't been keeping up with 64 bit or private futexes. What else
could probably go wrong?
Well, that's the point : This interface is like an ioctl() one : pretty bad if
not properly designed :)
You probably need to stick one field containing one command or version number,
something like that.
struct futex_event {
int type;
union {
void __user *addr;
u64 padding;
};
union {
int val;
s64 val64;
};
};
#define FUTEX_EVENT_SHARED32 1
#define FUTEX_EVENT_SHARED64 2
#define FUTEX_EVENT_PRIVATE32 (128|1)
#define FUTEX_EVENT_PRIVATE64 (128|2)
...
Also, you should take care of alignements constraints (a 32bit user program
might run on a 64bit kernel)
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