introduce safe_poll (fixes a problem in top)

function                                             old     new   delta
safe_poll                                              -      77     +77
svlogd_main                                         1470    1466      -4
zcip_main                                           1530    1524      -6
forkexec                                            1345    1338      -7
decode_format_string                                 795     788      -7
collect_blk                                          474     467      -7
buffer_pread                                         540     532      -8
tftp                                                1182    1172     -10
microcom_main                                        763     749     -14
arpping                                              441     424     -17
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/9 up/down: 77/-80)             Total: -3 bytes
   text    data     bss     dec     hex filename
 770162    1034   10404  781600   bed20 busybox_old
 770158    1034   10404  781596   bed1c busybox_unstripped

13 files changed, 65 insertions, 30 deletions

diff --git a/editors/vi.c b/editors/vi.c
index f5df41636..1fa7c3a09 100644
--- a/editors/vi.c
+++ b/editors/vi.c
@@ -2139,7 +2139,7 @@ static int mysleep(int hund)	// sleep for 'h' 1/100 seconds
 
 	pfd[0].fd = 0;
 	pfd[0].events = POLLIN;
-	return poll(pfd, 1, hund*10) > 0;
+	return safe_poll(pfd, 1, hund*10) > 0;
 }
 
 #define readbuffer bb_common_bufsiz1
@@ -2221,7 +2221,7 @@ static char readit(void)	// read (maybe cursor) key from stdin
 			pfd[0].events = POLLIN;
 			// Wait 50 ms
 			// keep reading while there are input chars and room in buffer
-			while (poll(pfd, 1, 50) > 0 && n <= (MAX_LINELEN - 5)) {
+			while (safe_poll(pfd, 1, 50) > 0 && n <= (MAX_LINELEN - 5)) {
 				// read the rest of the ESC string
 				int r = read(0, readbuffer + n, MAX_LINELEN - n);
 				if (r > 0)
diff --git a/include/libbb.h b/include/libbb.h
index 407b723b2..26a0f0d4a 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -451,8 +451,14 @@ extern FILE *fopen_or_warn(const char *filename, const char *mode);
 /* "Opens" stdin if filename is special, else just opens file: */
 extern FILE *fopen_or_warn_stdin(const char *filename);
 
+/* Wrapper which restarts poll on EINTR or ENOMEM.
+ * On other errors complains [perror("poll")] and returns.
+ * Warning! May take (much) longer than timeout_ms to return!
+ * If this is a problem, use bare poll and open-code EINTR/ENOMEM handling */
+int safe_poll(struct pollfd *ufds, nfds_t nfds, int timeout_ms);
+
 /* Convert each alpha char in str to lower-case */
-extern char* str_tolower(char *str);
+char* str_tolower(char *str);
 
 char *utoa(unsigned n);
 char *itoa(int n);
diff --git a/libbb/Kbuild b/libbb/Kbuild
index 1800bde8f..55b3658b4 100644
--- a/libbb/Kbuild
+++ b/libbb/Kbuild
@@ -71,6 +71,7 @@ lib-y += recursive_action.o
 lib-y += remove_file.o
 lib-y += restricted_shell.o
 lib-y += run_shell.o
+lib-y += safe_poll.o
 lib-y += safe_strncpy.o
 lib-y += safe_write.o
 lib-y += setup_environment.o
diff --git a/libbb/safe_poll.c b/libbb/safe_poll.c
new file mode 100644
index 000000000..d2b773c36
--- /dev/null
+++ b/libbb/safe_poll.c
@@ -0,0 +1,34 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Utility routines.
+ *
+ * Copyright (C) 2007 by Denys Vlasenko <vda.linux@googlemail.com>
+ *
+ * Licensed under GPLv2, see file LICENSE in this tarball for details.
+ */
+
+#include "libbb.h"
+
+/* Wrapper which restarts poll on EINTR or ENOMEM.
+ * On other errors does perror("poll") and returns.
+ * Warning! May take longer than timeout_ms to return! */
+int safe_poll(struct pollfd *ufds, nfds_t nfds, int timeout)
+{
+	while (1) {
+		int n = poll(ufds, nfds, timeout);
+		if (n >= 0)
+			return n;
+		/* Make sure we inch towards completion */
+		if (timeout > 0)
+			timeout--;
+		/* E.g. strace causes poll to return this */
+		if (errno == EINTR)
+			continue;
+		/* Kernel is very low on memory. Retry. */
+		/* I doubt many callers would handle this correctly! */
+		if (errno == ENOMEM)
+			continue;
+		bb_perror_msg("poll");
+		return n;
+	}
+}
diff --git a/libbb/safe_strncpy.c b/libbb/safe_strncpy.c
index ebc7e28f3..cc425839f 100644
--- a/libbb/safe_strncpy.c
+++ b/libbb/safe_strncpy.c
@@ -10,7 +10,7 @@
 #include "libbb.h"
 
 /* Like strncpy but make sure the resulting string is always 0 terminated. */
-char * safe_strncpy(char *dst, const char *src, size_t size)
+char *safe_strncpy(char *dst, const char *src, size_t size)
 {
 	if (!size) return dst;
 	dst[--size] = '\0';
diff --git a/miscutils/microcom.c b/miscutils/microcom.c
index 59a91024e..5928569d5 100644
--- a/miscutils/microcom.c
+++ b/miscutils/microcom.c
@@ -105,8 +105,7 @@ int microcom_main(int argc, char **argv)
 	pfd[1].events = POLLIN;
 	while (1) {
 		int i;
-		while (-1 == poll(pfd, 2, -1) && EINTR == errno)
-			continue;
+		safe_poll(pfd, 2, -1);
 		for (i = 0; i < 2; ++i) {
 			if (pfd[i].revents & POLLIN) {
 				len = read(pfd[i].fd, bb_common_bufsiz1, COMMON_BUFSIZE);
diff --git a/networking/httpd.c b/networking/httpd.c
index cedec800f..92a07107d 100644
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -1073,13 +1073,9 @@ static NOINLINE void cgi_io_loop_and_exit(int fromCgi_rd, int toCgi_wr, int post
 		}
 
 		/* Now wait on the set of sockets */
-		count = poll(pfd, 3, -1);
+		count = safe_poll(pfd, 3, -1);
 		if (count <= 0) {
 #if 0
-			if (errno == EINTR)
-				continue;
-#endif
-#if 0
 			if (waitpid(pid, &status, WNOHANG) <= 0) {
 				/* Weird. CGI didn't exit and no fd's
 				 * are ready, yet poll returned?! */
diff --git a/networking/tftp.c b/networking/tftp.c
index ac3a86afb..59f53ae4a 100644
--- a/networking/tftp.c
+++ b/networking/tftp.c
@@ -225,7 +225,7 @@ static int tftp( USE_GETPUT(const int cmd,)
 		/* Receive packet */
 		/*pfd[0].fd = socketfd;*/
 		pfd[0].events = POLLIN;
-		switch (poll(pfd, 1, waittime_ms)) {
+		switch (safe_poll(pfd, 1, waittime_ms)) {
 			unsigned from_port;
 		case 1:
 			from->len = peer_lsa->len;
@@ -262,7 +262,7 @@ static int tftp( USE_GETPUT(const int cmd,)
 
 			goto send_again; /* resend last sent pkt */
 		default:
-			bb_perror_msg("poll");
+			/*bb_perror_msg("poll"); - done in safe_poll */
 			goto ret;
 		}
  process_pkt:
diff --git a/networking/traceroute.c b/networking/traceroute.c
index 21921e56d..2d09c7197 100644
--- a/networking/traceroute.c
+++ b/networking/traceroute.c
@@ -543,7 +543,7 @@ wait_for_reply(int sock, struct sockaddr_in *fromp)
 
 	pfd[0].fd = sock;
 	pfd[0].events = POLLIN;
-	if (poll(pfd, 1, waittime * 1000) > 0)
+	if (safe_poll(pfd, 1, waittime * 1000) > 0)
 		cc = recvfrom(sock, packet, sizeof(packet), 0,
 			    (struct sockaddr *)fromp, &fromlen);
 	return cc;
diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index 33518077b..7b702d8f3 100644
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -81,12 +81,9 @@ int arpping(uint32_t test_ip, uint32_t from_ip, uint8_t *from_mac, const char *i
 		unsigned prevTime = monotonic_us();
 
 		pfd[0].events = POLLIN;
-		r = poll(pfd, 1, timeout_ms);
+		r = safe_poll(pfd, 1, timeout_ms);
 		if (r < 0) {
-			if (errno != EINTR) {
-				bb_perror_msg("poll");
-				break;
-			}
+			break;
 		} else if (r) {
 			if (read(s, &arp, sizeof(arp)) < 0)
 				break;
diff --git a/networking/zcip.c b/networking/zcip.c
index 2f0b5a7fb..63846ebef 100644
--- a/networking/zcip.c
+++ b/networking/zcip.c
@@ -300,7 +300,12 @@ int zcip_main(int argc, char **argv)
 
 		VDBG("...wait %d %s nprobes=%u, nclaims=%u\n",
 				timeout_ms, intf, nprobes, nclaims);
-		switch (poll(fds, 1, timeout_ms)) {
+
+		switch (safe_poll(fds, 1, timeout_ms)) {
+
+		default:
+			/*bb_perror_msg("poll"); - done in safe_poll */
+			return EXIT_FAILURE;
 
 		// timeout
 		case 0:
@@ -388,6 +393,7 @@ int zcip_main(int argc, char **argv)
 				break;
 			} // switch (state)
 			break; // case 0 (timeout)
+
 		// packets arriving
 		case 1:
 			// We need to adjust the timeout in case we didn't receive
@@ -519,13 +525,9 @@ int zcip_main(int argc, char **argv)
 				nclaims = 0;
 				break;
 			} // switch state
-
 			break; // case 1 (packets arriving)
-		default:
-			why = "poll";
-			goto bad;
 		} // switch poll
-	}
+	} // while (1)
  bad:
 	bb_perror_msg("%s, %s", intf, why);
 	return EXIT_FAILURE;
diff --git a/procps/top.c b/procps/top.c
index ac3b7e5a2..e55cecccb 100644
--- a/procps/top.c
+++ b/procps/top.c
@@ -924,7 +924,7 @@ int top_main(int argc, char **argv)
 #if !ENABLE_FEATURE_USE_TERMIOS
 		sleep(interval);
 #else
-		if (poll(pfd, 1, interval * 1000) != 0) {
+		if (safe_poll(pfd, 1, interval * 1000) > 0) {
 			if (read(0, &c, 1) != 1)    /* signal */
 				break;
 			if (c == initial_settings.c_cc[VINTR])
diff --git a/runit/svlogd.c b/runit/svlogd.c
index 6c8747e96..b5eed15ab 100644
--- a/runit/svlogd.c
+++ b/runit/svlogd.c
@@ -665,7 +665,7 @@ static ssize_t ndelay_read(int fd, void *buf, size_t count)
 }
 
 /* Used for reading stdin */
-static int buffer_pread(int fd, char *s, unsigned len)
+static int buffer_pread(/*int fd, */char *s, unsigned len)
 {
 	unsigned now;
 	struct pollfd input;
@@ -709,7 +709,7 @@ static int buffer_pread(int fd, char *s, unsigned len)
 		poll(&input, 1, i * 1000);
 		sigprocmask(SIG_BLOCK, blocked_sigset, NULL);
 
-		i = ndelay_read(fd, s, len);
+		i = ndelay_read(0, s, len);
 		if (i >= 0)
 			break;
 		if (errno == EINTR)
@@ -909,7 +909,7 @@ int svlogd_main(int argc, char **argv)
 		if (!np && !exitasap) {
 			i = linemax - stdin_cnt; /* avail. bytes at tail */
 			if (i >= 128) {
-				i = buffer_pread(0, lineptr + stdin_cnt, i);
+				i = buffer_pread(/*0, */lineptr + stdin_cnt, i);
 				if (i <= 0) /* EOF or error on stdin */
 					exitasap = 1;
 				else {
@@ -966,7 +966,7 @@ int svlogd_main(int argc, char **argv)
 		/* read/write repeatedly until we see it */
 		while (ch != '\n') {
 			/* lineptr is emptied now, safe to use as buffer */
-			stdin_cnt = exitasap ? -1 : buffer_pread(0, lineptr, linemax);
+			stdin_cnt = exitasap ? -1 : buffer_pread(/*0, */lineptr, linemax);
 			if (stdin_cnt <= 0) { /* EOF or error on stdin */
 				exitasap = 1;
 				lineptr[0] = ch = '\n';