tests: robustify attach-p-cmd.test against buggy kernels

From time to time various kernels, old and new, just go nuts
and fail attach-p-cmd.test with the following diagnostics:

 12345 --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
-12345 chdir("attach-p-cmd.test -p") = -1 ENOENT (No such file or directory)
+12345 syscall_4294967295(0xffe60934, 0x1c0, 0xffe60934, 0x1, 0xffe609b4, 0xffe60a58) = -1 (errno 38)
+12345 chdir("attach-p-cmd.test -p") = -1 ENOSYS (Function not implemented)

Let's workaround this kernel madness by rewriting the test
without use of SIGALRM.

* tests/attach-p-cmd.h: New file.
* tests/Makefile.am (EXTRA_DIST): Add attach-p-cmd.h.
* tests/attach-p-cmd-cmd.c: Include "attach-p-cmd.h".
(write_pidfile, wait_for_peer_invocation): New functions.
(main): Use them.
* tests/attach-p-cmd-p.c: Include <time.h> and "attach-p-cmd.h".
(wait_for_peer_invocation, wait_for_peer_termination): New functions.
(main): Use them.  Do not raise SIGALRM, use nanosleep after peer
termination.

tests/Makefile.am

@@ -316,6 +316,7 @@ VALGRIND_FLAGS = --quiet
 VALGRIND_SUPPRESSIONS_FILES = $(abs_srcdir)/strace.supp
 
 EXTRA_DIST = \
+	attach-p-cmd.h \
 	caps-abbrev.awk \
 	caps.awk \
 	clock.in \

tests/attach-p-cmd-cmd.c

@@ -1,7 +1,7 @@
 /*
  * This file is part of attach-p-cmd strace test.
  *
- * Copyright (c) 2016 Dmitry V. Levin <ldv@altlinux.org>
+ * Copyright (c) 2016-2017 Dmitry V. Levin <ldv@altlinux.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -32,19 +32,41 @@
 #include <stdio.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include "attach-p-cmd.h"
 
-int
+static void
-main(void)
+write_pidfile(const pid_t pid)
+{
+	FILE *fp = fopen(pidfile, "w");
+	if (!fp)
+		perror_msg_and_fail("fopen: %s", pidfile);
+
+	if (fprintf(fp, "%d", pid) < 0)
+		perror_msg_and_fail("fprintf: %s", pidfile);
+
+	if (fclose(fp))
+		perror_msg_and_fail("fclose: %s", pidfile);
+}
+
+static void
+wait_for_peer_invocation(void)
 {
-	static const char lockdir[] = "attach-p-cmd.test-lock";
 	/* wait for the lock directory to be created by peer */
 	while (rmdir(lockdir)) {
 		if (ENOENT != errno)
 			perror_msg_and_fail("rmdir: %s", lockdir);
 	}
+}
+
+int
+main(void)
+{
+	const pid_t pid = getpid();
+	write_pidfile(pid);
+
+	wait_for_peer_invocation();
 
 	static const char dir[] = "attach-p-cmd.test cmd";
-	pid_t pid = getpid();
 	int rc = chdir(dir);
 
 	printf("%-5d chdir(\"%s\") = %s\n"

tests/attach-p-cmd-p.c

@@ -1,7 +1,7 @@
 /*
  * This file is part of attach-p-cmd strace test.
  *
- * Copyright (c) 2016 Dmitry V. Levin <ldv@altlinux.org>
+ * Copyright (c) 2016-2017 Dmitry V. Levin <ldv@altlinux.org>
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -33,27 +33,14 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/stat.h>
+#include <time.h>
 #include <unistd.h>
+#include "attach-p-cmd.h"
 
 static void
-handler(int signo)
+wait_for_peer_invocation(void)
 {
-}
+	/* create the lock directory */
-
-int
-main(void)
-{
-	const struct sigaction act = { .sa_handler = handler };
-	if (sigaction(SIGALRM, &act, NULL))
-		perror_msg_and_fail("sigaction");
-
-	sigset_t mask = {};
-	sigaddset(&mask, SIGALRM);
-	if (sigprocmask(SIG_UNBLOCK, &mask, NULL))
-		perror_msg_and_fail("sigprocmask");
-
-	static const char lockdir[] = "attach-p-cmd.test-lock";
-	/* create a lock directory */
 	if (mkdir(lockdir, 0700))
 		perror_msg_and_fail("mkdir: %s", lockdir);
 
@@ -63,21 +50,51 @@ main(void)
 			perror_msg_and_fail("mkdir: %s", lockdir);
 	}
 
-	/* remove the lock directory */
+	/* cleanup the lock directory */
 	if (rmdir(lockdir))
 		perror_msg_and_fail("rmdir: %s", lockdir);
+}
 
-	alarm(1);
+static void
-	pause();
+wait_for_peer_termination(void)
+{
+	FILE *fp = fopen(pidfile, "r");
+	if (!fp)
+		perror_msg_and_fail("fopen: %s", pidfile);
+
+	pid_t pid;
+	if (fscanf(fp, "%d", &pid) < 0)
+		perror_msg_and_fail("fscanf: %s", pidfile);
+	if (pid < 0)
+		error_msg_and_fail("pid = %d", pid);
+
+	if (fclose(fp))
+		perror_msg_and_fail("fclose: %s", pidfile);
+
+	if (unlink(pidfile))
+		perror_msg_and_fail("unlink: %s", pidfile);
+
+	while (kill(pid, 0) == 0)
+		;
+}
+
+int
+main(void)
+{
+	wait_for_peer_invocation();
+	wait_for_peer_termination();
+
+	static const struct timespec ts = { .tv_nsec = 123456789 };
+	if (nanosleep(&ts, NULL))
+		perror_msg_and_fail("nanosleep");
 
 	static const char dir[] = "attach-p-cmd.test -p";
 	pid_t pid = getpid();
 	int rc = chdir(dir);
 
-	printf("%-5d --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---\n"
+	printf("%-5d chdir(\"%s\") = %s\n"
-	       "%-5d chdir(\"%s\") = %d %s (%m)\n"
 	       "%-5d +++ exited with 0 +++\n",
-	       pid, pid, dir, rc, errno2name(), pid);
+	       pid, dir, sprintrc(rc), pid);
 
 	return 0;
 }

tests/attach-p-cmd.h

@@ -0,0 +1,2 @@
+static const char lockdir[] = "attach-p-cmd.test-lock";
+static const char pidfile[] = "attach-p-cmd.test-pid";