cmp: Print a summary on SIGINFO.

MFC after:	1 week
Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D38280

usr.bin/cmp/cmp.c

@@ -75,6 +75,17 @@ static const struct option long_opts[] =
 	{NULL,		no_argument,		NULL, 0}
 };
 
+#ifdef SIGINFO
+volatile sig_atomic_t info;
+
+static void
+siginfo(int signo)
+{
+
+	info = signo;
+}
+#endif
+
 static void usage(void);
 
 static bool
@@ -240,6 +251,9 @@ main(int argc, char *argv[])
 		}
 	}
 
+#ifdef SIGINFO
+	(void)signal(SIGINFO, siginfo);
+#endif
 	if (special)
 		c_special(fd1, file1, skip1, fd2, file2, skip2, limit);
 	else {

usr.bin/cmp/extern.h

@@ -46,3 +46,7 @@ void	diffmsg(const char *, const char *, off_t, off_t, int, int);
 void	eofmsg(const char *);
 
 extern bool bflag, lflag, sflag, xflag, zflag;
+
+#ifdef SIGINFO
+extern volatile sig_atomic_t info;
+#endif

usr.bin/cmp/regular.c

@@ -120,6 +120,13 @@ c_regular(int fd1, const char *file1, off_t skip1, off_t len1,
 	p2 = m2 + (skip2 - off2);
 
 	for (byte = line = 1; length--; ++byte) {
+#ifdef SIGINFO
+		if (info) {
+			(void)fprintf(stderr, "%s %s char %zu line %zu\n",
+			    file1, file2, (size_t)byte, (size_t)line);
+			info = 0;
+		}
+#endif
 		if ((ch = *p1) != *p2) {
 			if (xflag) {
 				dfound = 1;

usr.bin/cmp/special.c

@@ -77,6 +77,13 @@ c_special(int fd1, const char *file1, off_t skip1,
 			goto eof;
 
 	for (byte = line = 1; limit == 0 || byte <= limit; ++byte) {
+#ifdef SIGINFO
+		if (info) {
+			(void)fprintf(stderr, "%s %s char %zu line %zu\n",
+			    file1, file2, (size_t)byte, (size_t)line);
+			info = 0;
+		}
+#endif
 		ch1 = getc(fp1);
 		ch2 = getc(fp2);
 		if (ch1 == EOF || ch2 == EOF)