Re: [PATCH v2 1/2] tools subcmd: Add non-waitpid check_if_command_finished()

From: Ian Rogers
Date: Wed Jul 03 2024 - 00:29:02 EST


On Tue, Jul 2, 2024 at 8:24 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hi Ian,
>
> On Sun, Jun 30, 2024 at 09:42:35PM -0700, Ian Rogers wrote:
> > Using waitpid can cause stdout/stderr of the child process to be
> > lost. Use Linux's /prod/<pid>/status file to determine if the process
> > has reached the zombie state. Use the 'status' file rather than 'stat'
> > to avoid issues around skipping the process name.
> >
> > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> > ---
> > tools/lib/subcmd/run-command.c | 33 +++++++++++++++++++++++++++++++++
> > 1 file changed, 33 insertions(+)
> >
> > diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
> > index 4e3a557a2f37..ec06683e77a0 100644
> > --- a/tools/lib/subcmd/run-command.c
> > +++ b/tools/lib/subcmd/run-command.c
> > @@ -2,6 +2,7 @@
> > #include <unistd.h>
> > #include <sys/types.h>
> > #include <sys/stat.h>
> > +#include <ctype.h>
> > #include <fcntl.h>
> > #include <string.h>
> > #include <linux/string.h>
> > @@ -217,8 +218,40 @@ static int wait_or_whine(struct child_process *cmd, bool block)
> >
> > int check_if_command_finished(struct child_process *cmd)
> > {
> > +#ifdef __linux__
>
> Is this really necessary? I don't think we plan to support other OS..

I don't think it'd be unreasonable to say run "perf report" on
Windows, or using wasm inside a web browser. Part of the reason for
doing things this way was to keep the WNOHANG logic although this
change no longer uses it for __linux__.

Thanks,
Ian

> Thanks,
> Namhyung
>
>
> > + char filename[FILENAME_MAX + 12];
> > + char status_line[256];
> > + FILE *status_file;
> > +
> > + /*
> > + * Check by reading /proc/<pid>/status as calling waitpid causes
> > + * stdout/stderr to be closed and data lost.
> > + */
> > + sprintf(filename, "/proc/%d/status", cmd->pid);
> > + status_file = fopen(filename, "r");
> > + if (status_file == NULL) {
> > + /* Open failed assume finish_command was called. */
> > + return true;
> > + }
> > + while (fgets(status_line, sizeof(status_line), status_file) != NULL) {
> > + char *p;
> > +
> > + if (strncmp(status_line, "State:", 6))
> > + continue;
> > +
> > + fclose(status_file);
> > + p = status_line + 6;
> > + while (isspace(*p))
> > + p++;
> > + return *p == 'Z';
> > + }
> > + /* Read failed assume finish_command was called. */
> > + fclose(status_file);
> > + return true;
> > +#else
> > wait_or_whine(cmd, /*block=*/false);
> > return cmd->finished;
> > +#endif
> > }
> >
> > int finish_command(struct child_process *cmd)
> > --
> > 2.45.2.803.g4e1b14247a-goog
> >