On Mon, Nov 26, 2012 at 11:03 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Mon, Nov 26, 2012 at 2:08 AM, Karel Zak <kzak@xxxxxxxxxx> wrote:
>>
>> It would be nice to have prctl(1) implemented like prlimit(1), it
>> means to support --set as well as --get operations.
>>
>> prctl --set-endian=big --set-name=foo
>>
>> prctl --pid 123 # return all --get-*
>>
>> prctl --get-name --pid 123
>>
>>> I also notice the similar capsh(1) program for doing
>>> so with capabilities. Perhaps these could be merged
>>> to a setpriv(1) command or something for tweaking all
>>> these knobs before exec?
>>
>> hmm.. capsh(1) is libcap baby and it probably makes sense to maintain
>> it on the same place like libcap.
>
> Taking a quick look through prctl:
>
>
> PR_GET/SET_CHILD_SUBREAPER: Very useful, but probably wants to be its own tool
>
For example, the tool below would probably be quite handy, but I don't
think it would make too much sense as part of a hypothetical prctl(1).
(I'll send this as a proper patch later on, after I make its
interface a little less silly.)
---wait_all_descendents.c---
#include <stdio.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/prctl.h>
#include <unistd.h>
#include <errno.h>
static volatile sig_atomic_t exec_failed = 0;
static volatile int exec_errno;
static int wait_all_children(pid_t child_pid)
{
while (1) {
siginfo_t si;
if (waitid(P_ALL, 0, &si, WEXITED) != 0) {
if (errno == ECHILD) {
if (child_pid)
fprintf(stderr, "Warning: child never exited\n");
return 0;
} else {
perror("waitid");
return 1;
}
}
if (si.si_pid == child_pid) {
child_pid = 0;
fprintf(stderr, "Immediate child exited\n");
}
}
}
int main(int argc, char **argv)
{
if (argc < 2) {
printf("Usage: wait_descendents PROGRAM [ARGS]...\n");
return 1;
}
if (signal(SIGCHLD, SIG_DFL)) {
perror("signal");
return 127;
}
if (prctl(PR_SET_CHILD_SUBREAPER, 1, 0, 0, 0) != 0) {
perror("PR_SET_CHILD_SUBREAPER");
return 127;
}
pid_t child_pid = vfork();
if (child_pid == -1) {
perror("fork");
return 1;
} else if (child_pid == 0) {
/* We're the child. */
execvp(argv[1], argv + 1);
exec_failed = 1;
exec_errno = errno;
_exit(1);
} else {
if (exec_failed) {
errno = exec_errno;
perror(argv[1]);
return 127;
}
return wait_all_children(child_pid);
}
}
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