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Subjectsignalfd() not handling sigqueue() sigval data correctly
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Hi Davide,

I was doing some playing about with signalfd(), and seem to have encountered a
bug: when a signalfd read() fetches data for a signal that was sent by
sigqueue(), the data accompanying the signal is not returned. Instead
ssi_int/ssi_ptr is zero.

I've not looked into the cause of the problem, but the programs below can be
used to demonstrate it.

Here's an example run:

# Run in the background, waiting for signal 44.
$ ./signalfd_sigval 44 &
./signalfd_sigval: PID = 14783
[1] 14783
# Send signal 44 to PID 14783 with accompanying data 123
$ ./sigqueue 14783 44 123
/home/mtk/alp/signals/sigqueue: PID = 14784
Got signal 44
ssi_code= -1
ssi_pid = 14784
ssi_uid = 1000
ssi_int = 0 <= should be 123 here
ssi_ptr = 0 <= and here the hex version of 123

Could you take a look at this?

Cheers,

Michael


/* signalfd_sigval.c */

#define _GNU_SOURCE
#include <sys/syscall.h>
#include <unistd.h>
#include <stdint.h>
#include <signal.h>
#if defined(__i386__)
#define __NR_signalfd 321
#endif

struct signalfd_siginfo {
uint32_t ssi_signo;
int32_t ssi_errno;
int32_t ssi_code;
uint32_t ssi_pid;
uint32_t ssi_uid;
int32_t ssi_fd;
uint32_t ssi_tid;
uint32_t ssi_band;
uint32_t ssi_overrun;
uint32_t ssi_trapno;
int32_t ssi_status;
int32_t ssi_int;
uint64_t ssi_ptr;
uint64_t ssi_utime;
uint64_t ssi_stime;
uint64_t ssi_addr;
uint8_t __pad[48];
};

static int
signalfd(int ufd, sigset_t const *mask)
{
#define SIZEOF_SIG (_NSIG / 8)
#define SIZEOF_SIGSET (SIZEOF_SIG > sizeof(sigset_t) ? \
sizeof(sigset_t): SIZEOF_SIG)
return syscall(__NR_signalfd, ufd, mask, SIZEOF_SIGSET);
}

// #include <sys/signalfd.h>
#include <signal.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); } while (0)

int
main(int argc, char *argv[])
{
sigset_t mask;
int sfd;
struct signalfd_siginfo fdsi;
ssize_t s;

if (argc != 2) {
fprintf(stderr, "Usage: %s sig-num\n", argv[0]);
exit(EXIT_FAILURE);
}

printf("%s: PID = %ld\n", argv[0], (long) getpid());

sigemptyset(&mask);
sigaddset(&mask, atoi(argv[1]));

if (sigprocmask(SIG_BLOCK, &mask, NULL) == -1)
errExit("sigprocmask");

sfd = signalfd(-1, &mask);
if (sfd == -1)
errExit("signalfd");

for (;;) {
s = read(sfd, &fdsi, sizeof(struct signalfd_siginfo));
if (s != sizeof(struct signalfd_siginfo))
errExit("read");

printf("Got signal %d\n", fdsi.ssi_signo);
printf(" ssi_code= %d\n", fdsi.ssi_code);
printf(" ssi_pid = %d\n", fdsi.ssi_pid);
printf(" ssi_uid = %d\n", fdsi.ssi_uid);
printf(" ssi_int = %d\n", fdsi.ssi_int);
printf(" ssi_ptr = %llx\n", fdsi.ssi_ptr);
}
}



/* sigqueue.c */

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)

int
main(int argc, char *argv[])
{
union sigval sv;

if (argc != 4) {
fprintf(stderr, "Usage: %s pid sig-num data\n", argv[0]);
exit(EXIT_FAILURE);
}

printf("%s: PID = %ld\n", argv[0], (long) getpid());

sv.sival_int = atoi(argv[3]);
if (sigqueue(atoi(argv[1]), atoi(argv[2]), sv) == -1)
errExit("sigqueue");

exit(EXIT_SUCCESS);
}



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