[PATCH] sys_poll(): fix function definition/negative timeout values

[PATCH] sys_poll(): fix function definition/negative timeout values

[Thomas Meyer]

Fix negative timeout values for x86 userland on x86_64 kernels.
Align sys_poll() definition to glibc's definition.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
---
 fs/select.c              |    2 +-
 include/linux/syscalls.h |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/select.c b/fs/select.c
index d33418f..e782258 100644
--- a/fs/select.c
+++ b/fs/select.c
@@ -912,7 +912,7 @@ static long do_restart_poll(struct restart_block *restart_block)
 }
 
 SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
-		long, timeout_msecs)
+		int, timeout_msecs)
 {
 	struct timespec end_time, *to = NULL;
 	int ret;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 1ff0ec2..8f482e5 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -624,7 +624,7 @@ asmlinkage long sys_socketpair(int, int, int, int __user *);
 asmlinkage long sys_socketcall(int call, unsigned long __user *args);
 asmlinkage long sys_listen(int, int);
 asmlinkage long sys_poll(struct pollfd __user *ufds, unsigned int nfds,
-				long timeout);
+				int timeout);
 asmlinkage long sys_select(int n, fd_set __user *inp, fd_set __user *outp,
 			fd_set __user *exp, struct timeval __user *tvp);
 asmlinkage long sys_old_select(struct sel_arg_struct __user *arg);
-- 
1.7.6.2

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Andi Kleen]

Thomas Meyer <thomas@m3y3r.de> writes:

> Fix negative timeout values for x86 userland on x86_64 kernels.
> Align sys_poll() definition to glibc's definition.

Nack. Please write a compat wrapper that sign extends.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Eric Dumazet]

Le jeudi 15 septembre 2011 à 10:47 -0700, Andi Kleen a écrit :
> Thomas Meyer <thomas@m3y3r.de> writes:
> 
> > Fix negative timeout values for x86 userland on x86_64 kernels.
> > Align sys_poll() definition to glibc's definition.
> 
> Nack. Please write a compat wrapper that sign extends.
> 

Why ?

man poll

int poll(struct pollfd *ufds, unsigned int nfds, int delay); 

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Andi Kleen]

On Thu, Sep 15, 2011 at 08:05:17PM +0200, Eric Dumazet wrote:
> Le jeudi 15 septembre 2011 à 10:47 -0700, Andi Kleen a écrit :
> > Thomas Meyer <thomas@m3y3r.de> writes:
> > 
> > > Fix negative timeout values for x86 userland on x86_64 kernels.
> > > Align sys_poll() definition to glibc's definition.
> > 
> > Nack. Please write a compat wrapper that sign extends.
> > 
> 
> Why ?

Because we shouldn't change existing interfaces and there could
be valid reasons on 64bit for really long delays.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Eric Dumazet]

Le jeudi 15 septembre 2011 à 20:12 +0200, Andi Kleen a écrit :
> On Thu, Sep 15, 2011 at 08:05:17PM +0200, Eric Dumazet wrote:
> > Le jeudi 15 septembre 2011 à 10:47 -0700, Andi Kleen a écrit :
> > > Thomas Meyer <thomas@m3y3r.de> writes:
> > > 
> > > > Fix negative timeout values for x86 userland on x86_64 kernels.
> > > > Align sys_poll() definition to glibc's definition.
> > > 
> > > Nack. Please write a compat wrapper that sign extends.
> > > 
> > 
> > Why ?
> 
> Because we shouldn't change existing interfaces and there could
> be valid reasons on 64bit for really long delays.

I disagree.

Existing interface and POSIX mandates "int delay"

The kernel part of the contract was fine when we supported 32bit only
machines, by chance, because sizeof(int) == sizeof(long).

If you want more than 31 bits delay, then we need a new interface, and
this new interface must also work on 32bit arches (sort of poll64())

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Andrew Morton]

On Thu, 15 Sep 2011 20:21:02 +0200
Eric Dumazet <eric.dumazet@gmail.com> wrote:

> Le jeudi 15 septembre 2011 __ 20:12 +0200, Andi Kleen a __crit :
> > On Thu, Sep 15, 2011 at 08:05:17PM +0200, Eric Dumazet wrote:
> > > Le jeudi 15 septembre 2011 __ 10:47 -0700, Andi Kleen a __crit :
> > > > Thomas Meyer <thomas@m3y3r.de> writes:
> > > > 
> > > > > Fix negative timeout values for x86 userland on x86_64 kernels.
> > > > > Align sys_poll() definition to glibc's definition.
> > > > 
> > > > Nack. Please write a compat wrapper that sign extends.
> > > > 
> > > 
> > > Why ?
> > 
> > Because we shouldn't change existing interfaces and there could
> > be valid reasons on 64bit for really long delays.
> 
> I disagree.
> 
> Existing interface and POSIX mandates "int delay"
> 
> The kernel part of the contract was fine when we supported 32bit only
> machines, by chance, because sizeof(int) == sizeof(long).
> 
> If you want more than 31 bits delay, then we need a new interface, and
> this new interface must also work on 32bit arches (sort of poll64())

So what's happening here?

If the change will break (or alter) existing code which does

	poll(..., something_greater_than_2g)

then I don't think we can apply the patch.  There may be code out there
which breaks, there may not be.  We don't know.  We screwed up, we get
to wear the cost of having done so.

Re: [PATCH] sys_poll(): fix function definition/negative timeout values

[Valdis.Kletnieks]

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On Thu, 15 Sep 2011 14:45:56 +0200, Thomas Meyer said:
> Fix negative timeout values for x86 userland on x86_64 kernels.
> Align sys_poll() definition to glibc's definition.

> -		long, timeout_msecs)
> +		int, timeout_msecs)

Is this going to surprise a non-glibc userspace on any platforms?

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