Hi.
In this thread[1] we've been discussing whether you can
get an invalid answer if you open /proc/loadavg because
of a context switch in the kernel.
I read your howto about the seq_fs[2], but the callback of
the /proc/loadavg uses the old method.
I read the function and I notice that it expects to write all
the data at one (and doesn't honor count, ie: uses sprintf
instead of snprintf).
So, my questions are:
- Is the following call of sprintf atomic?
- Is there a non-zero probability of getting wrong
data from this call or a similar one?
Thanks.
linux-2.6.13.2/fs/proc/proc_misc.c:
--------------------------------------------------
static int loadavg_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
int a, b, c;
int len;
a = avenrun[0] + (FIXED_1/200);
b = avenrun[1] + (FIXED_1/200);
c = avenrun[2] + (FIXED_1/200);
len = sprintf(page,"%d.%02d %d.%02d %d.%02d %ld/%d %d\n",
LOAD_INT(a), LOAD_FRAC(a),
LOAD_INT(b), LOAD_FRAC(b),
LOAD_INT(c), LOAD_FRAC(c),
nr_running(), nr_threads, last_pid);
return proc_calc_metrics(page, start, off, count, eof, len);
}
[1]http://lists.debian.org/debian-isp/2005/10/threads.html#00011
[2]http://www.kernelnewbies.org/documents/seq_file_howto.txt
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