util-net: Make send/recv fds carry fd flags in message

The flags are only one bit in the kernel (close-on-exec, all the rest are not per-fd, but per-file),
but for simplicity I save it in a char field.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/util-net.h

@@ -25,22 +25,23 @@ struct scm_fdset {
 	struct msghdr	hdr;
 	struct iovec	iov;
 	char		msg_buf[CR_SCM_MSG_SIZE];
-	int		msg;	/* We are to send at least one byte */
+	char		msg[CR_SCM_MAX_FD];
 };
 
-extern int send_fds(int sock, struct sockaddr_un *saddr, int saddr_len, int *fds, int nr_fds);
-extern int recv_fds(int sock, int *fds, int nr_fds);
+extern int send_fds(int sock, struct sockaddr_un *saddr, int saddr_len,
+		int *fds, int nr_fds, bool with_flags);
+extern int recv_fds(int sock, int *fds, int nr_fds, char *flags);
 
 static inline int send_fd(int sock, struct sockaddr_un *saddr, int saddr_len, int fd)
 {
-	return send_fds(sock, saddr, saddr_len, &fd, 1);
+	return send_fds(sock, saddr, saddr_len, &fd, 1, false);
 }
 
 static inline int recv_fd(int sock)
 {
 	int fd, ret;
 
-	ret = recv_fds(sock, &fd, 1);
+	ret = recv_fds(sock, &fd, 1, NULL);
 	if (ret)
 		return -1;
 

parasite-syscall.c

@@ -583,7 +583,7 @@ int parasite_drain_fds_seized(struct parasite_ctl *ctl, int *fds, int *lfds, int
 		goto err;
 	}
 
-	ret = recv_fds(sock, lfds, nr_fds);
+	ret = recv_fds(sock, lfds, nr_fds, NULL);
 	if (ret) {
 		pr_err("Can't retrieve FDs from socket\n");
 		goto err;

parasite.c

@@ -373,7 +373,7 @@ static int drain_fds(struct parasite_drain_fd *args)
 	int ret;
 
 	ret = send_fds(tsock, &args->saddr, args->sun_len,
-		       args->fds, args->nr_fds);
+		       args->fds, args->nr_fds, false);
 	if (ret) {
 		sys_write_msg("send_fds failed\n");
 		SET_PARASITE_RET(st, ret);

util-net.c

@@ -20,17 +20,16 @@ static void scm_fdset_init_chunk(struct scm_fdset *fdset, int nr_fds)
 	cmsg->cmsg_len	= fdset->hdr.msg_controllen;
 }
 
-static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr, int saddr_len)
+static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr,
+		int saddr_len, bool with_flags)
 {
 	struct cmsghdr *cmsg;
 
 	BUILD_BUG_ON(CR_SCM_MAX_FD > SCM_MAX_FD);
 	BUILD_BUG_ON(sizeof(fdset->msg_buf) < (CMSG_SPACE(sizeof(int) * CR_SCM_MAX_FD)));
 
-	fdset->msg			= '*';
-
 	fdset->iov.iov_base		= &fdset->msg;
-	fdset->iov.iov_len		= sizeof(fdset->msg);
+	fdset->iov.iov_len		= with_flags ? sizeof(fdset->msg) : 1;
 
 	fdset->hdr.msg_iov		= &fdset->iov;
 	fdset->hdr.msg_iovlen		= 1;
@@ -48,18 +47,33 @@ static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr, i
 	return (int *)CMSG_DATA(cmsg);
 }
 
-int send_fds(int sock, struct sockaddr_un *saddr, int len, int *fds, int nr_fds)
+int send_fds(int sock, struct sockaddr_un *saddr, int len,
+		int *fds, int nr_fds, bool with_flags)
 {
 	struct scm_fdset fdset;
 	int *cmsg_data;
 	int i, min_fd, ret;
 
-	cmsg_data = scm_fdset_init(&fdset, saddr, len);
+	cmsg_data = scm_fdset_init(&fdset, saddr, len, with_flags);
 	for (i = 0; i < nr_fds; i += min_fd) {
 		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
 		scm_fdset_init_chunk(&fdset, min_fd);
 		builtin_memcpy(cmsg_data, &fds[i], sizeof(int) * min_fd);
 
+		if (with_flags) {
+			int j;
+
+			for (j = 0; j < min_fd; j++) {
+				int flags;
+
+				flags = sys_fcntl(fds[i + j], F_GETFD, 0);
+				if (flags < 0)
+					return -1;
+
+				fdset.msg[j] = (char)flags;
+			}
+		}
+
 		ret = sys_sendmsg(sock, &fdset.hdr, 0);
 		if (ret <= 0)
 			return ret ? : -1;
@@ -68,7 +82,7 @@ int send_fds(int sock, struct sockaddr_un *saddr, int len, int *fds, int nr_fds)
 	return 0;
 }
 
-int recv_fds(int sock, int *fds, int nr_fds)
+int recv_fds(int sock, int *fds, int nr_fds, char *flags)
 {
 	struct scm_fdset fdset;
 	struct cmsghdr *cmsg;
@@ -76,7 +90,7 @@ int recv_fds(int sock, int *fds, int nr_fds)
 	int ret;
 	int i, min_fd;
 
-	cmsg_data = scm_fdset_init(&fdset, NULL, 0);
+	cmsg_data = scm_fdset_init(&fdset, NULL, 0, flags != NULL);
 	for (i = 0; i < nr_fds; i += min_fd) {
 		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
 		scm_fdset_init_chunk(&fdset, min_fd);
@@ -104,6 +118,8 @@ int recv_fds(int sock, int *fds, int nr_fds)
 		if (unlikely(min_fd <= 0))
 			return -1;
 		builtin_memcpy(&fds[i], cmsg_data, sizeof(int) * min_fd);
+		if (flags)
+			builtin_memcpy(flags, fdset.msg, sizeof(char) * min_fd);
 	}
 
 	return 0;