debugging rlimit

[Eric Blake]

How am I supposed to debug code related to rlimit, when it appears that
gdb/strace resets it to default values?

$ cat foo.c
#include <stdio.h>
#include <unistd.h>
#include <sys/resource.h>
int main(void) {
struct rlimit r;
if (!getrlimit(RLIMIT_NOFILE, &r))
printf("%ld %ld\n", r.rlim_cur, r.rlim_max);
return 0;
}
$ ./foo
256 3200
$ (ulimit -n 1000; ./foo)
1000 3200
$ (ulimit -n 1000; strace -o /dev/null ./foo)
256 3200

Since rlimit is intertwined with getdtablesize(), I'd like to be able to
debug a process that starts with a different limit than normal.

[Corinna Vinschen]

Post by Eric Blake
How am I supposed to debug code related to rlimit, when it appears that
gdb/strace resets it to default values?
$ cat foo.c
#include <stdio.h>
#include <unistd.h>
#include <sys/resource.h>
int main(void) {
struct rlimit r;
if (!getrlimit(RLIMIT_NOFILE, &r))
printf("%ld %ld\n", r.rlim_cur, r.rlim_max);
return 0;
}
$ ./foo
256 3200
$ (ulimit -n 1000; ./foo)
1000 3200
$ (ulimit -n 1000; strace -o /dev/null ./foo)
256 3200
Since rlimit is intertwined with getdtablesize(), I'd like to be able to
debug a process that starts with a different limit than normal.

You can workaround this problem by attaching to the process after it
started. In the dumbest possible way, you can add something like this
to main:

1 printf ("PID %u, waiting...\n", getpid ());
2 sleep (10);
3 printf ("Here I am\n");

Attach to the process during the sleep period, and, in GDB, set a
breakpoint to line 3 and continue execution.


Corinna