waitpid: support 'PID:inode' process addressing format

Adding support for the 'PID:inode' format to address a
process ensures that waitpid(1) safely polls the status
of the expected process in a race-free manner. Worthy of
note is that with the addition of the getino(1) command
the aforementioned task becomes trivially simple.

Example:
        waitpid $(getino -p 123456)

Signed-off-by: Christian Goeschel Ndjomouo <cgoesc2@wgu.edu>

diff --git a/misc-utils/waitpid.c b/misc-utils/waitpid.c
index b9b88c32818268071ea8aa1cd7dcafa59052e270..d73a393c09f3f6905b9c92238b2f30f50b17c2e4 100644 (file)
--- a/misc-utils/waitpid.c
+++ b/misc-utils/waitpid.c
@@ -35,6 +35,7 @@
 #include "exitcodes.h"
 #include "timeutils.h"
 #include "optutils.h"
+#include "pidutils.h"
 
 #define EXIT_TIMEOUT_EXPIRED 3
 
@@ -43,6 +44,7 @@
 struct process_info {
        pid_t           pid;
        int             pidfd;
+       uint64_t        pidfd_ino;
 };
 
 /* list of processes specified by PIDs on the command line */
@@ -57,19 +59,35 @@ struct waitpid_control {
        struct timespec timeout;
 };
 
-static void parse_pids(struct process_info *pinfos, size_t n_strings, char * const *strings)
+static void parse_pids_or_err(struct process_info *pinfos, size_t n_strings, char * const *strings)
 {
        for (size_t i = 0; i < n_strings; i++) {
-               pinfos[i].pid = strtopid_or_err(strings[i], _("invalid PID argument"));
+               struct process_info *pi = &pinfos[i];
+               ul_parse_pid_str_or_err(strings[i], &pi->pid, &pi->pidfd_ino);
        }
 }
 
-static void open_pidfds(const struct waitpid_control *ctl, struct process_info *pinfos, size_t n_pids)
+static inline int get_pidfd(const struct waitpid_control *ctl, struct process_info *pi)
+{
+       int fd;
+
+       if (pi->pidfd_ino) {
+               fd = ul_get_valid_pidfd(pi->pid, pi->pidfd_ino);
+               if (fd < 0 && ctl->verbose)
+                       warnx(_("pidfd inode %"PRIu64" not found for pid %d"),
+                                       pi->pidfd_ino, pi->pid);
+       } else {
+               fd = pidfd_open(pi->pid, 0);
+       }
+       return fd;
+}
+
+static void open_pidfds_or_err(const struct waitpid_control *ctl, struct process_info *pinfos, size_t n_pids)
 {
        for (size_t i = 0; i < n_pids; i++) {
                struct process_info *pi = &pinfos[i];
 
-               pi->pidfd = pidfd_open(pi->pid, 0);
+               pi->pidfd = get_pidfd(ctl, pi);
                if (pi->pidfd < 0) {
                        if (ctl->allow_exited && errno == ESRCH) {
                                if (ctl->verbose)
@@ -165,9 +183,14 @@ static void wait_for_exits(const struct waitpid_control *ctl, int epll,
 static void __attribute__((__noreturn__)) usage(void)
 {
        FILE *out = stdout;
-
+       char *pid_arg = NULL;
+#ifdef USE_PIDFD_INO_SUPPORT
+       pid_arg = "PID[:inode]";
+#else
+       pid_arg = "PID";
+#endif
        fputs(USAGE_HEADER, out);
-       fprintf(out, _(" %s [options] pid...\n"), program_invocation_short_name);
+       fprintf(out, _(" %s [options] %s...\n"), program_invocation_short_name, pid_arg);
 
        fputs(USAGE_OPTIONS, out);
        fputs(_(" -v, --verbose           be more verbose\n"), out);
@@ -255,8 +278,8 @@ int main(int argc, char **argv)
 
        proc_infos = xcalloc(n_pids, sizeof(*proc_infos));
 
-       parse_pids(proc_infos, argc - pid_idx, argv + pid_idx);
-       open_pidfds(&ctl, proc_infos, n_pids);
+       parse_pids_or_err(proc_infos, argc - pid_idx, argv + pid_idx);
+       open_pidfds_or_err(&ctl, proc_infos, n_pids);
 
        timeoutfd = open_timeoutfd(&ctl);
        epoll = epoll_create(n_pids);