Re: [PATCH] ring-buffer: Fix polling on trace_pipe

Martin Lau
2014-07-15T20:20:50Z

Yes, I think it should go to both stable and 3.16.

Thanks,
--Martin

On Tue, Jul 15, 2014 at 03:46:12PM -0400, Steven Rostedt wrote:
> On Thu, 10 Jul 2014 15:20:30 -0700
> Martin Lau <kafai@fb.com> wrote:
>
> > Hi Steve,
> >
> > Do you have a chance to give it another try?
> >
>
> OK, I finally got around to testing it. Yep I see your point. Do you
> think it should go to 3.16 and stable? I can add it to my next git pull
> request.
>
> Also, I modified your test such that it wouldn't hang on failure, but
> detects that it hung and returns a exit value to add this to my
> testing. That is, it exits with zero on success and non zero on failure.
>
> -- Steve

> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/types.h>
> #include <sys/wait.h>
> #include <sys/stat.h>
> #include <sys/epoll.h>
> #include <fcntl.h>
> #include <unistd.h>
> #include <assert.h>
> #include <signal.h>
> #include <errno.h>
>
> static const char * debugfs_list[] = {
> "/debug/tracing",
> "/sys/kernel/debug/tracing",
> "/d/tracing",
> NULL,
> };
>
> static const char *debugfs;
> static int markfd;
> static int trace_pipe_fd;
>
> static void alog(const char *name, int ret)
> {
> printf("%d: %s: %d\n", getpid(), name, ret);
> }
>
> static const char *find_debugfs(void)
> {
> struct stat st;
> int i;
> int r;
>
> for (i = 0; debugfs_list[i]; i++) {
> r = stat(debugfs_list[i], &st);
> if (r < 0)
> continue;
> if (S_ISDIR(st.st_mode))
> return debugfs_list[i];
> }
> return NULL;
> }
>
> static char * make_path(const char *file)
> {
> char *path;
> int size;
>
> size = strlen(debugfs) + strlen(file) + 2;
> path = malloc(size);
> if (!path) {
> perror("malloc");
> exit(-1);
> }
> sprintf(path, "%s/%s", debugfs, file);
> return path;
> }
>
> static void mark_write(const char *str)
> {
> int ret;
> ret = write(markfd, str, strlen(str));
> alog("write(markfd)", ret);
> }
>
> static void read_trace_pipe(void)
> {
> char buf[1024];
> int r;
>
> while ((r = read(trace_pipe_fd, buf, 1024)) > 0)
> printf("%.*s", r, buf);
> }
>
> int main (int argc, char **argv)
> {
> struct epoll_event ee;
> char *marker;
> char *pipe;
> int efd;
> int ret;
> pid_t dwrt_pid;
>
> debugfs = find_debugfs();
> if (!debugfs) {
> fprintf(stderr, "Could not find debugfs\n");
> exit(-1);
> }
>
> marker = make_path("trace_marker");
> pipe = make_path("trace_pipe");
>
> markfd = open(marker, O_WRONLY);
> if (markfd < 0) {
> perror("marker");
> exit(-1);
> }
> trace_pipe_fd = open(pipe, O_RDONLY|O_NONBLOCK);
> if (trace_pipe_fd < 0) {
> perror("trace_pipe");
> exit(-1);
> }
>
> efd = epoll_create(1);
> if (efd < 0) {
> perror("epoll_create");
> exit(-1);
> }
>
> mark_write("some data");
> memset(&ee, 0, sizeof(ee));
> ee.events = EPOLLIN;
> ret = epoll_ctl(efd, EPOLL_CTL_ADD, trace_pipe_fd, &ee);
> if (ret < 0) {
> perror("epoll_ctl");
> exit(-1);
> }
> alog("waiting data......", 0);
> ret = epoll_wait(efd, &ee, 1, -1);
> alog("epoll_wait()", ret);
> read_trace_pipe();
> dwrt_pid = fork();
> assert(dwrt_pid != -1);
> if (dwrt_pid > 0) {
> int status;
> sleep(10);
> mark_write("more data");
> sleep(10);
> ret = waitpid(dwrt_pid, &status, WNOHANG);
> if (ret != dwrt_pid) {
> alog("Poll never finished!", 0);
> kill(dwrt_pid, 9);
> exit(-1);
> }
> if (WEXITSTATUS(status) != 0) {
> alog("Something failed on polling!",
> WEXITSTATUS(status));
> exit(-1);
> }
> } else {
> alog("waiting form more data......", 0);
> ret = epoll_wait(efd, &ee, 1, -1);
> alog("epoll_wait()", ret);
> read_trace_pipe();
> if (ret < 0)
> exit(errno);
> }
> exit (0);
> }