pgrep: add pwait

.gitignore

@@ -39,6 +39,7 @@ pgrep
 pidof
 pkill
 pmap
+pwait
 procps-ng-*.tar.xz
 proc/.depend
 proc/libprocps.la

Makefile.am

@@ -49,6 +49,9 @@ bin_PROGRAMS = \
 	uptime \
 	vmstat \
 	w
+if BUILD_PWAIT
+bin_PROGRAMS += pwait
+endif
 else
 usrbin_exec_PROGRAMS += \
 	ps/pscommand \
@@ -81,6 +84,10 @@ dist_man_MANS += \
 	sysctl.8 \
 	sysctl.conf.5 \
 	ps/ps.1
+
+if BUILD_PWAIT
+dist_man_MANS += pwait.1
+endif
 endif
 
 EXTRA_DIST = \
@@ -192,6 +199,9 @@ free_SOURCES = free.c lib/strutils.c lib/fileutils.c
 pgrep_SOURCES = pgrep.c lib/fileutils.c lib/nsutils.c
 pkill_SOURCES = pgrep.c lib/fileutils.c lib/nsutils.c
 pmap_SOURCES = pmap.c lib/fileutils.c
+if BUILD_PWAIT
+pwait_SOURCES = pgrep.c lib/fileutils.c lib/nsutils.c
+endif
 if !CYGWIN
 pwdx_SOURCES = pwdx.c lib/fileutils.c
 pwdx_LDADD= $(CYGWINFLAGS)

configure.ac

@@ -10,6 +10,7 @@ AM_INIT_AUTOMAKE([foreign 1.11 subdir-objects -Wall -Wno-portability tar-pax no-
 AM_SILENT_RULES([yes])
 AC_CONFIG_SRCDIR([free.c])
 AC_CONFIG_HEADERS([config.h])
+AC_LANG([C])
 
 # Checks for programs.
 AC_USE_SYSTEM_EXTENSIONS
@@ -125,6 +126,21 @@ AC_TRY_COMPILE([#include <errno.h>],
 		AC_MSG_RESULT(yes),
 		AC_MSG_RESULT(no))
 
+AC_CHECK_FUNC([pidfd_open], [enable_pwait=yes], [
+  AC_MSG_CHECKING([for __NR_pidfd_open])
+  AC_COMPILE_IFELSE([AC_LANG_SOURCE([
+#include <sys/syscall.h>
+#ifndef __NR_pidfd_open
+#error __NR_pidfd_open not defined
+#endif
+    ])], [enable_pwait=yes], [enable_pwait=no])
+  AC_MSG_RESULT([$enable_pwait])
+])
+if test "$enable_pwait" = yes; then
+  AC_DEFINE([ENABLE_PWAIT], [1], [Enable pwait])
+fi
+AM_CONDITIONAL([BUILD_PWAIT], [test x$enable_pwait = xyes])
+
 dnl watch8bit must be before the AC_ARG_WITH set as it sets up ncurses
 AC_SUBST([WITH_WATCH8BIT])
 AC_ARG_ENABLE([watch8bit],

pgrep.1

@@ -9,13 +9,16 @@
 .\"
 .TH PGREP "1" "2020-06-04" "procps-ng" "User Commands"
 .SH NAME
-pgrep, pkill \- look up or signal processes based on name and other attributes
+pgrep, pkill, pwait \- look up, signal, or wait for processes based on name and other attributes
 .SH SYNOPSIS
 .B pgrep
 [options] pattern
 .br
 .B pkill
 [options] pattern
+.br
+.B pwait
+[options] pattern
 .SH DESCRIPTION
 .B pgrep
 looks through the currently running processes and lists the process IDs which
@@ -41,6 +44,9 @@ OR
 will send the specified signal (by default
 .BR SIGTERM )
 to each process instead of listing them on stdout.
+.PP
+.B pwait
+will wait for each process instead of listing them on stdout.
 .SH OPTIONS
 .TP
 \fB\-\fR\fIsignal\fP
@@ -54,7 +60,9 @@ only.)
 \fB\-c\fR, \fB\-\-count\fR
 Suppress normal output; instead print a count of matching processes.  When
 count does not match anything, e.g. returns zero, the command will return
-non-zero value.
+non-zero value. Note that for pkill and pwait, the count is the number of
+matching processes, not the processes that were successfully signaled or waited
+for.
 .TP
 \fB\-d\fR, \fB\-\-delimiter\fR \fIdelimiter\fP
 Sets the string used to delimit each process ID in the output (by default a
@@ -77,9 +85,10 @@ is set, the full command line is used.
 \fB\-g\fR, \fB\-\-pgroup\fR \fIpgrp\fP,...
 Only match processes in the process group IDs listed.  Process group 0 is
 translated into
-.BR pgrep 's
+.BR pgrep 's,
+.BR pkill 's,
 or
-.BR pkill 's
+.BR pwait 's
 own process group.
 .TP
 \fB\-G\fR, \fB\-\-group\fR \fIgid\fP,...
@@ -114,9 +123,10 @@ Only match processes whose parent process ID is listed.
 \fB\-s\fR, \fB\-\-session\fR \fIsid\fP,...
 Only match processes whose process session ID is listed.  Session ID 0
 is translated into
-.BR pgrep 's
+.BR pgrep 's,
+.BR pkill 's,
 or
-.BR pkill 's
+.BR pwait 's
 own session ID.
 .TP
 \fB\-t\fR, \fB\-\-terminal\fR \fIterm\fP,...
@@ -134,6 +144,8 @@ symbolical value may be used.
 \fB\-v\fR, \fB\-\-inverse\fR\fR
 Negates the matching.  This option is usually used in
 .BR pgrep 's
+or
+.BR pwait 's
 context.  In
 .BR pkill 's
 context the short option is disabled to avoid accidental usage of the option.
@@ -141,6 +153,8 @@ context the short option is disabled to avoid accidental usage of the option.
 \fB\-w\fR, \fB\-\-lightweight\fR\fR
 Shows all thread ids instead of pids in
 .BR pgrep 's
+or
+.BR pwait 's
 context.  In
 .BR pkill 's
 context this option is disabled.
@@ -152,8 +166,8 @@ match the
 .IR pattern .
 .TP
 \fB\-F\fR, \fB\-\-pidfile\fR \fIfile\fR
-Read \fIPID\fRs from \fIfile\fR.  This option is perhaps more useful for
+Read \fIPID\fRs from \fIfile\fR.  This option is more useful for
-.B pkill
+.BR pkill or pwait
 than
 .BR pgrep .
 .TP
@@ -223,8 +237,8 @@ $ renice +4 $(pgrep chrome)
 .PD 0
 .TP
 0
-One or more processes matched the criteria. For pkill the process must also
+One or more processes matched the criteria. For pkill and pwait, one or more
-have been successfully signalled.
+processes must also have been successfully signalled or waited for.
 .TP
 1
 No processes matched or none of them could be signalled.
@@ -241,9 +255,10 @@ the output of /proc/\fIpid\fP/stat.  Use the \fB\-f\fR option to match against t
 complete command line, /proc/\fIpid\fP/cmdline.
 .PP
 The running
-.B pgrep
+.BR pgrep ,
+.BR pkill ,
 or
-.B pkill
+.B pwait
 process will never report itself as a
 match.
 .SH BUGS

pgrep.c

@@ -38,6 +38,11 @@
 #include <stdbool.h>
 #include <time.h>
 
+#if defined(ENABLE_PWAIT) && !defined(HAVE_PIDFD_OPEN)
+#include <sys/epoll.h>
+#include <sys/syscall.h>
+#endif
+
 /* EXIT_SUCCESS is 0 */
 /* EXIT_FAILURE is 1 */
 #define EXIT_USAGE 2
@@ -60,7 +65,13 @@
 	(x) = (x) * 5 / 4 + 4; \
 } while (0)
 
-static int i_am_pkill = 0;
+static enum {
+    PGREP = 0,
+    PKILL,
+#ifdef ENABLE_PWAIT
+    PWAIT,
+#endif
+} prog_mode;
 
 struct el {
 	long	num;
@@ -112,17 +123,24 @@ static int __attribute__ ((__noreturn__)) usage(int opt)
 	fputs(USAGE_HEADER, fp);
 	fprintf(fp, _(" %s [options] <pattern>\n"), program_invocation_short_name);
 	fputs(USAGE_OPTIONS, fp);
-	if (i_am_pkill == 0) {
+	switch (prog_mode) {
+	case PGREP:
 		fputs(_(" -d, --delimiter <string>  specify output delimiter\n"),fp);
 		fputs(_(" -l, --list-name           list PID and process name\n"),fp);
 		fputs(_(" -a, --list-full           list PID and full command line\n"),fp);
 		fputs(_(" -v, --inverse             negates the matching\n"),fp);
 		fputs(_(" -w, --lightweight         list all TID\n"), fp);
-	}
+		break;
-	if (i_am_pkill == 1) {
+	case PKILL:
 		fputs(_(" -<sig>, --signal <sig>    signal to send (either number or name)\n"), fp);
 		fputs(_(" -q, --queue <value>       integer value to be sent with the signal\n"), fp);
 		fputs(_(" -e, --echo                display what is killed\n"), fp);
+		break;
+#ifdef ENABLE_PWAIT
+	case PWAIT:
+		fputs(_(" -e, --echo                display PIDs before waiting\n"), fp);
+		break;
+#endif
 	}
 	fputs(_(" -c, --count               count of matching processes\n"), fp);
 	fputs(_(" -f, --full                use full process name to match\n"), fp);
@@ -669,11 +687,8 @@ static struct el * select_procs (int *num)
 				xerrx(EXIT_FAILURE, _("internal error"));
 			}
 
-			// pkill does not need subtasks!
+			// pkill and pwait don't support -w, but this is checked in getopt
-			// this control is still done at
+			if (opt_threads) {
-			// argparse time, but a further
-			// control is free
-			if (opt_threads && !i_am_pkill) {
 				while (readtask(ptp, &task, &subtask)){
 					// don't add redundant tasks
 					if (task.XXXID == subtask.XXXID)
@@ -722,6 +737,13 @@ static int signal_option(int *argc, char **argv)
 	return -1;
 }
 
+#if defined(ENABLE_PWAIT) && !defined(HAVE_PIDFD_OPEN)
+static int pidfd_open (pid_t pid, unsigned int flags)
+{
+	return syscall(__NR_pidfd_open, pid, flags);
+}
+#endif
+
 static void parse_opts (int argc, char **argv)
 {
 	char opts[64] = "";
@@ -766,16 +788,21 @@ static void parse_opts (int argc, char **argv)
 		{NULL, 0, NULL, 0}
 	};
 
-	if (strstr (program_invocation_short_name, "pkill")) {
+#ifdef ENABLE_PWAIT
+	if (strcmp (program_invocation_short_name, "pwait") == 0) {
+		prog_mode = PWAIT;
+		strcat (opts, "e");
+	} else
+#endif
+        if (strcmp (program_invocation_short_name, "pkill") == 0) {
 		int sig;
-		i_am_pkill = 1;
+		prog_mode = PKILL;
 		sig = signal_option(&argc, argv);
 		if (-1 < sig)
 			opt_signal = sig;
-		/* These options are for pkill only */
 		strcat (opts, "eq:");
 	} else {
-		/* These options are for pgrep only */
+		prog_mode = PGREP;
 		strcat (opts, "lad:vw");
 	}
 
@@ -974,6 +1001,14 @@ int main (int argc, char **argv)
 {
 	struct el *procs;
 	int num;
+	int i;
+	int kill_count = 0;
+#ifdef ENABLE_PWAIT
+	int poll_count = 0;
+	int wait_count = 0;
+	int epollfd = epoll_create(1);
+	struct epoll_event ev, events[32];
+#endif
 
 #ifdef HAVE_PROGRAM_INVOCATION_NAME
 	program_invocation_name = program_invocation_short_name;
@@ -986,9 +1021,19 @@ int main (int argc, char **argv)
 	parse_opts (argc, argv);
 
 	procs = select_procs (&num);
-	if (i_am_pkill) {
+	switch (prog_mode) {
-		int i;
+	case PGREP:
-		int kill_count = 0;
+		if (opt_count) {
+			fprintf(stdout, "%d\n", num);
+		} else {
+			if (opt_long || opt_longlong)
+				output_strlist (procs,num);
+			else
+				output_numlist (procs,num);
+		}
+		return !num;
+
+	case PKILL:
 		for (i = 0; i < num; i++) {
 			if (execute_kill (procs[i].num, opt_signal) != -1) {
 				if (opt_echo)
@@ -1004,15 +1049,41 @@ int main (int argc, char **argv)
 		if (opt_count)
 			fprintf(stdout, "%d\n", num);
 		return !kill_count;
-	} else {
+
-		if (opt_count) {
+#ifdef ENABLE_PWAIT
+	case PWAIT:
+		if (opt_count)
 			fprintf(stdout, "%d\n", num);
-		} else {
+
-			if (opt_long || opt_longlong)
+		for (i = 0; i < num; i++) {
-				output_strlist (procs,num);
+			if (opt_echo)
-			else
+				printf(_("waiting for %s (pid %lu)\n"), procs[i].str, procs[i].num);
-				output_numlist (procs,num);
+			int pidfd = pidfd_open(procs[i].num, 0);
+			if (pidfd == -1) {
+				/* ignore ESRCH, same as pkill */
+				if (errno != ESRCH)
+					xwarn(_("opening pid %ld failed"), procs[i].num);
+				continue;
 			}
+			ev.events = EPOLLIN | EPOLLET;
+			ev.data.fd = pidfd;
+			if (epoll_ctl(epollfd, EPOLL_CTL_ADD, pidfd, &ev) != -1)
+				poll_count++;
 		}
-	return !num; /* exit(EXIT_SUCCESS) if match, otherwise exit(EXIT_FAILURE) */
+
+		while (wait_count < poll_count) {
+			int ew = epoll_wait(epollfd, events, sizeof(events)/sizeof(events[0]), -1);
+			if (ew == -1) {
+				if (errno == EINTR)
+					continue;
+				xwarn(_("epoll_wait failed"));
+			}
+			wait_count += ew;
+		}
+
+		return !wait_count;
+#endif
+	}
+    /* Not sure if it is possible to get here */
+    return -1;
 }

pwait.1

@@ -0,0 +1 @@
+.so man1/pgrep.1