socket: Fix select failing when the process has many file descriptors by using poll instead

This happens, for example, when a process links with libusbmuxd, and the process is file descriptor heavy.
Note: 'poll' means the syscall poll, not a polling approach. This patch does not add a busy wait and is not a performance regression.

1 files changed, 100 insertions, 79 deletions

diff --git a/src/socket.c b/src/socket.c
index 48eb831..49a5ef4 100644
--- a/src/socket.c
+++ b/src/socket.c
@@ -65,6 +65,7 @@ static int wsa_init = 0;
 #endif
 #include "common.h"
 #include "libimobiledevice-glue/socket.h"
+#include <sys/poll.h>
 
 #define RECV_TIMEOUT 20000
 #define SEND_TIMEOUT 10000
@@ -140,6 +141,80 @@ LIBIMOBILEDEVICE_GLUE_API const char *socket_addr_to_string(struct sockaddr *add
 	return NULL;
 }
 
+enum poll_status
+{
+	poll_status_success,
+	poll_status_timeout,
+	poll_status_error
+};
+
+// timeoutMilliseconds of -1 means infinity
+static enum poll_status poll_wrapper(int fd, fd_mode mode, int timeoutMilliseconds)
+{
+	// https://man7.org/linux/man-pages/man2/select.2.html
+	// Correspondence between select() and poll() notifications
+	// #define POLLIN_SET  (EPOLLRDNORM | EPOLLRDBAND | EPOLLIN |
+	//                      EPOLLHUP | EPOLLERR)
+	//                    /* Ready for reading */
+	// #define POLLOUT_SET (EPOLLWRBAND | EPOLLWRNORM | EPOLLOUT |
+	//                      EPOLLERR)
+	//                    /* Ready for writing */
+	// #define POLLEX_SET  (EPOLLPRI)
+	//                    /* Exceptional condition */
+
+	short events;
+	switch(mode)
+	{
+		case FDM_READ:
+			events = POLLRDNORM | POLLRDBAND | POLLIN | POLLHUP | POLLERR;
+			break;
+		case FDM_WRITE:
+			events = POLLWRBAND | POLLWRNORM | POLLOUT | POLLERR;
+			break;
+		case FDM_EXCEPT:
+			events = POLLPRI;
+			break;
+		default:
+			if (verbose >= 2)
+				fprintf(stderr, "%s: fd_mode %d unsupported\n", __func__, mode);
+			return poll_status_error;
+	}
+	while(1)
+	{
+		struct pollfd pfd = {
+			.fd = fd,
+			.events = events,
+		};
+		switch(poll(&pfd, 1, timeoutMilliseconds))
+		{
+			case 1:
+				if((pfd.revents & (POLLNVAL | POLLERR)) != 0)
+				{
+					if (verbose >= 2)
+						fprintf(stderr, "%s: poll unexpected events: %d\n", __func__,
+								(int)pfd.revents);
+					return poll_status_error;
+				}
+				return poll_status_success;
+			case 0:
+				return poll_status_timeout;
+			case -1:
+				if(errno == EINTR)
+				{
+					if (verbose >= 2)
+						fprintf(stderr, "%s: EINTR\n", __func__);
+					continue;
+				}
+				// fallthrough
+			default:
+				if (verbose >= 2)
+					fprintf(stderr, "%s: poll failed: %s\n", __func__,
+							strerror(errno));
+				return poll_status_error;
+		}
+	}
+}
+
 #ifndef WIN32
 LIBIMOBILEDEVICE_GLUE_API int socket_create_unix(const char *filename)
 {
@@ -246,14 +321,7 @@ LIBIMOBILEDEVICE_GLUE_API int socket_connect_unix(const char *filename)
 			break;
 		}
 		if (errno == EINPROGRESS) {
-			fd_set fds;
-			FD_ZERO(&fds);
-			FD_SET(sfd, &fds);
-
-			struct timeval timeout;
-			timeout.tv_sec = CONNECT_TIMEOUT / 1000;
-			timeout.tv_usec = (CONNECT_TIMEOUT - (timeout.tv_sec * 1000)) * 1000;
-			if (select(sfd + 1, NULL, &fds, NULL, &timeout) == 1) {
+			if(poll_wrapper(sfd, FDM_WRITE, CONNECT_TIMEOUT) == poll_status_success) {
 				int so_error;
 				socklen_t len = sizeof(so_error);
 				getsockopt(sfd, SOL_SOCKET, SO_ERROR, (void*)&so_error, &len);
@@ -930,14 +998,7 @@ LIBIMOBILEDEVICE_GLUE_API int socket_connect_addr(struct sockaddr* addr, uint16_
 		if (errno == EINPROGRESS)
 #endif
 		{
-			fd_set fds;
-			FD_ZERO(&fds);
-			FD_SET(sfd, &fds);
-
-			struct timeval timeout;
-			timeout.tv_sec = CONNECT_TIMEOUT / 1000;
-			timeout.tv_usec = (CONNECT_TIMEOUT - (timeout.tv_sec * 1000)) * 1000;
-			if (select(sfd + 1, NULL, &fds, NULL, &timeout) == 1) {
+			if(poll_wrapper(sfd, FDM_WRITE, CONNECT_TIMEOUT) == poll_status_success) {
 				int so_error;
 				socklen_t len = sizeof(so_error);
 				getsockopt(sfd, SOL_SOCKET, SO_ERROR, (void*)&so_error, &len);
@@ -1054,14 +1115,7 @@ LIBIMOBILEDEVICE_GLUE_API int socket_connect(const char *addr, uint16_t port)
 		if (errno == EINPROGRESS)
 #endif
 		{
-			fd_set fds;
-			FD_ZERO(&fds);
-			FD_SET(sfd, &fds);
-
-			struct timeval timeout;
-			timeout.tv_sec = CONNECT_TIMEOUT / 1000;
-			timeout.tv_usec = (CONNECT_TIMEOUT - (timeout.tv_sec * 1000)) * 1000;
-			if (select(sfd + 1, NULL, &fds, NULL, &timeout) == 1) {
+			if(poll_wrapper(sfd, FDM_WRITE, CONNECT_TIMEOUT) == poll_status_success) {
 				int so_error;
 				socklen_t len = sizeof(so_error);
 				getsockopt(sfd, SOL_SOCKET, SO_ERROR, (void*)&so_error, &len);
@@ -1098,70 +1152,37 @@ LIBIMOBILEDEVICE_GLUE_API int socket_connect(const char *addr, uint16_t port)
 
 LIBIMOBILEDEVICE_GLUE_API int socket_check_fd(int fd, fd_mode fdm, unsigned int timeout)
 {
-	fd_set fds;
-	int sret;
-	int eagain;
-	struct timeval to;
-	struct timeval *pto;
-
 	if (fd < 0) {
 		if (verbose >= 2)
 			fprintf(stderr, "ERROR: invalid fd in check_fd %d\n", fd);
 		return -1;
 	}
 
-	FD_ZERO(&fds);
-	FD_SET(fd, &fds);
-
-	sret = -1;
-
-	do {
-		if (timeout > 0) {
-			to.tv_sec = (time_t) (timeout / 1000);
-			to.tv_usec = (time_t) ((timeout - (to.tv_sec * 1000)) * 1000);
-			pto = &to;
-		} else {
-			pto = NULL;
-		}
-		eagain = 0;
-		switch (fdm) {
-		case FDM_READ:
-			sret = select(fd + 1, &fds, NULL, NULL, pto);
-			break;
-		case FDM_WRITE:
-			sret = select(fd + 1, NULL, &fds, NULL, pto);
-			break;
-		case FDM_EXCEPT:
-			sret = select(fd + 1, NULL, NULL, &fds, pto);
-			break;
-		default:
-			return -1;
-		}
+	int timeoutMilliseconds;
+	if(timeout > 0)
+	{
+		timeoutMilliseconds = (int)timeout;
+		if(timeoutMilliseconds <= 0)
+			timeoutMilliseconds = -1;
+	}
+	else
+	{
+		timeoutMilliseconds = -1;
+	}
 
-		if (sret < 0) {
-			switch (errno) {
-			case EINTR:
-				// interrupt signal in select
-				if (verbose >= 2)
-					fprintf(stderr, "%s: EINTR\n", __func__);
-				eagain = 1;
-				break;
-			case EAGAIN:
-				if (verbose >= 2)
-					fprintf(stderr, "%s: EAGAIN\n", __func__);
-				break;
-			default:
-				if (verbose >= 2)
-					fprintf(stderr, "%s: select failed: %s\n", __func__,
-							strerror(errno));
-				return -1;
-			}
-		} else if (sret == 0) {
+	switch(poll_wrapper(fd, fdm, timeoutMilliseconds))
+	{
+		case poll_status_success:
+			return 1;
+		case poll_status_timeout:
 			return -ETIMEDOUT;
-		}
-	} while (eagain);
+		case poll_status_error:
+			if (verbose >= 2)
+				fprintf(stderr, "%s: poll_wrapper failed\n", __func__);
+			return -1;
+	}
 
-	return sret;
+	return -1;
 }
 
 LIBIMOBILEDEVICE_GLUE_API int socket_accept(int fd, uint16_t port)