lkml.org 
[lkml]   [2007]   [Jul]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: Fwd: timerfd read only gets single byte?
Michael Kerrisk wrote:
>
> Hi Davide,
>
> While writing a test program to incorporate into the timerfd.2 man page, I
> think I've found a bug. It looks like only the least significant byte of
> ticks is being returned from read(2), even though I am providing a 4 byte
> buffer.
>
> The test program takes 3 command line arguments:
>
> 1) seconds for the initial expiration
> 2) seconds for the timer interval
> 3) number of timer expirations to catch before terminating
>
> I tried running this program and suspending it for a few minutes, to see if
> I could get a large overrun value. When I do this on 2.6.22-rc4 (the built
> kernel I have to hand), I see the following:
>
> ============
> $ ./timerfd_demo 1 1 500
> 0.000: timer started
> 1.005: read: 1; total=1
> 2.005: read: 1; total=2
> 3.005: read: 1; total=3
> 4.005: read: 1; total=4
> 5.006: read: 1; total=5
> ^Z
> [1]+ Stopped ./timerfd_demo 1 1 500
> $ date
> Tue Jul 17 09:18:11 CEST 2007
> $ date
> Tue Jul 17 09:23:40 CEST 2007
> $ fg
> ./timerfd_demo 1 1 500
> 339.769: read: 78; total=83
> 340.004: read: 1; total=84
> 341.004: read: 1; total=85
> ^C
> ==============
>
> The after bringing the program back into the foreground, I would have
> expected to get an overrun count of 334 or thereabouts, but it looks as
> though I'm only getting the least significant byte from read(2).
>
> Cheers,
>
> Michael
>
> [...]

put_user copies sizeof(*ptr) bytes to user space.

Signed-off-by: Davi Arnaut <davi@haxent.com.br


diff --git a/fs/timerfd.c b/fs/timerfd.c
index af9eca5..e9f73f5 100644
--- a/fs/timerfd.c
+++ b/fs/timerfd.c
@@ -140,7 +140,8 @@ static ssize_t timerfd_read(struct file *file, char
__user *buf, size_t count,
}
spin_unlock_irq(&ctx->wqh.lock);
if (ticks)
- res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks);
+ res = put_user(ticks, ((u32 __user *)buf)) ? -EFAULT :
+ sizeof(ticks);
return res;
}

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2007-07-17 13:43    [W:0.033 / U:0.004 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site