hello list,
when doing "cat /proc/uptime" or similar files, the
routine which prepares the buffer gets called twice.
this is because "cat" reads two times from the file,
as a system-call-trace shows:
# strace -f cat /proc/uptime
...
read(3, "5241.09 5082.74\n", 1024) = 16
...
read(3, "", 1024) = 0
...
this leads to uptime_read_proc() being called two times,
the second time with parameter off=16, but since this
is ignored, the work is done twice: clock_...gettime(),
cputime_to_timespec(), sprintf(), proc_calc_metrics()
and so on.
insert a printk-statement if you don't beleive this.
btw, there's no wrong information produced because of this,
because *page points to the same location both calls.
a simple way to get rid of this:
static int uptime_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
struct timespec uptime;
struct timespec idle;
int len;
cputime_t idletime;
+ if (off)
+ return 0;
cputime_add(init_task.utime, init_task.stime);
do_posix_clock_monotonic_gettime(&uptime);
cputime_to_timespec(idletime, &idle);
len = sprintf(page,"%lu.%02lu %lu.%02lu\n",
...
and so on.
this affects possibly all /proc files which ignore the offset parameter
and are evaluated(?) with "cat".
regards,
h.rosmanith
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