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SubjectRe: [PATCH 2.6.25-4] getdelays.c: signal handling for log rotation
Scott Wiersdorf wrote:
> This adds a USR1 signal handler to getdelays.c, which causes getdelays
> to close its logfile and reopen it (if '-w logfile' is
> specified). This is useful in situations when getdelays is running for
> a long time (i.e, the log file growing) and you need to rotate the
> logs but don't want to lose any log data.
>
> Signed-off-by: Scott Wiersdorf <scott@perlcode.org>
> ---
> --- Documentation/accounting/getdelays.c 2008-05-15 09:00:12.000000000 -0600
> +++ Documentation/accounting/getdelays.c 2008-06-05 02:23:57.000000000 -0600
> @@ -50,6 +50,7 @@ int dbg;
> int print_delays;
> int print_io_accounting;
> int print_task_context_switch_counts;
> +volatile sig_atomic_t reopen_log = 0;



> __u64 stime, utime;
>
> #define PRINTF(fmt, arg...) { \
> @@ -80,6 +81,7 @@ static void usage(void)
> fprintf(stderr, " -l: listen forever\n");
> fprintf(stderr, " -v: debug on\n");
> fprintf(stderr, " -C: container path\n");
> + fprintf(stderr, "\nSend USR1 to reopen the logfile if -w is used.\n");

Please mention that old data will be lost and that SIGUSR1 will take affect
after some data is received.

> }
>
> /*
> @@ -231,6 +233,30 @@ void print_ioacct(struct taskstats *t)
> (unsigned long long)t->cancelled_write_bytes);
> }
>
> +void catch_usr1(int sig)
> +{
> + reopen_log = 1;
> + signal(sig, catch_usr1);
> +}
> +

Aren't we better of using the newer sigaction primitives? IIRC, signal can be
racy. The man page states "Avoid its use"

> +int reopen_logfile(int fd, char *logfile)
> +{
> + if (fd) {
> + PRINTF("USR1 received. Closing logfile.\n");
> + close(fd);

So sending USR1 causes data to be lost?

> + }
> + fd = open(logfile, O_WRONLY | O_CREAT | O_TRUNC,
> + S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
> + if (fd == -1) {
> + perror("Cannot open output file\n");
> + exit(1);
> + }
> +
> + reopen_log = 0;
> +
> + return fd;
> +}
> +
> int main(int argc, char *argv[])
> {
> int c, rc, rep_len, aggr_len, len2, cmd_type;
> @@ -320,12 +346,8 @@ int main(int argc, char *argv[])
> }
>
> if (write_file) {
> - fd = open(logfile, O_WRONLY | O_CREAT | O_TRUNC,
> - S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
> - if (fd == -1) {
> - perror("Cannot open output file\n");
> - exit(1);
> - }
> + fd = reopen_logfile(fd, logfile);
> + signal(SIGUSR1, catch_usr1); /* only set when write_file is set */
> }
>
> if ((nl_sd = create_nl_socket(NETLINK_GENERIC)) < 0)
> @@ -444,6 +466,9 @@ int main(int argc, char *argv[])
> err(1,"write error\n");
> }
> }
> + if (reopen_log) {
> + fd = reopen_logfile(fd, logfile);
> + }

This seems way of the 80 character space. You have braces that are not required.

> if (!loop)
> goto done;
> break;
>


--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL


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