add fd passing functions

CHANGES

@@ -1,5 +1,6 @@
 0.19:
   add io_socketpair
+  add io_passfd and io_receivefd (and test/fdpassing.c)
 
 0.18:
   make libowfat compile on BSD again (sorry, and thanks to everyone who

io.h

@@ -7,12 +7,16 @@
 #include "taia.h"
 
 /* like open(s,O_RDONLY) */
+/* return 1 if ok, 0 on error */
 int io_readfile(int64* d,const char* s);
 /* like open(s,O_WRONLY|O_CREAT|O_TRUNC,0600) */
+/* return 1 if ok, 0 on error */
 int io_createfile(int64* d,const char* s);
 /* like pipe(d) */
+/* return 1 if ok, 0 on error */
 int io_pipe(int64* d);
 /* like socketpair() */
+/* return 1 if ok, 0 on error */
 int io_socketpair(int64* d);
 
 /* non-blocking read(), -1 for EAGAIN and -3+errno for other errors */
@@ -82,6 +86,14 @@ void io_finishandshutdown(void);
 /* return number of bytes written */
 int64 io_sendfile(int64 s,int64 fd,uint64 off,uint64 n);
 
+/* Pass fd over sock (must be a unix domain socket) to other process.
+ * Return 0 if ok, -1 on error, setting errno. */
+int io_passfd(int64 sock,int64 fd);
+
+/* Receive fd over sock (must be a unix domain socket) from other
+ * process.  Return sock if ok, -1 on error, setting errno. */
+int64 io_receivefd(int64 sock);
+
 #ifdef __MINGW32__
 #include_next <io.h>
 #endif

io/io_passfd.c

@@ -0,0 +1,32 @@
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/uio.h>
+#include <errno.h>
+#include "io_internal.h"
+
+union fdmsg {
+  struct cmsghdr h;
+  char buf[CMSG_SPACE(sizeof(int))];
+};
+
+int io_passfd(int64 sock,int64 fd) {
+  struct msghdr msg = {0};
+  struct cmsghdr *cmsg;
+  struct iovec  iov;
+  char buf[CMSG_SPACE(sizeof(int))];
+  iov.iov_len=1;
+  iov.iov_base="x";
+  msg.msg_control = buf;
+  msg.msg_controllen = sizeof buf;
+  msg.msg_iov=&iov;
+  msg.msg_iovlen=1;
+  msg.msg_name=0;
+  msg.msg_namelen=0;
+  cmsg = CMSG_FIRSTHDR(&msg);
+  cmsg->cmsg_level = SOL_SOCKET;
+  cmsg->cmsg_type = SCM_RIGHTS;
+  cmsg->cmsg_len = CMSG_LEN(sizeof(int));
+  *((int*)CMSG_DATA(cmsg))=fd;
+  msg.msg_controllen = cmsg->cmsg_len;
+  return sendmsg(sock,&msg,0);
+}

io/io_receivefd.c

@@ -0,0 +1,45 @@
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/uio.h>
+#include <errno.h>
+#include "io_internal.h"
+
+union fdmsg {
+  struct cmsghdr h;
+  char buf[CMSG_SPACE(sizeof(int))];
+};
+
+int64 io_receivefd(int64 sock) {
+  struct iovec iov;
+  struct msghdr msg;
+  union fdmsg cmsg;
+  struct cmsghdr* h;
+  char x[100];
+  char name[100];
+  iov.iov_base=x;
+  iov.iov_len=100;
+  msg.msg_name=name;
+  msg.msg_namelen=100;
+  msg.msg_control=cmsg.buf;
+  msg.msg_controllen=sizeof(union fdmsg);
+  msg.msg_iov = &iov;
+  msg.msg_iovlen = 1;
+  msg.msg_flags=0;
+  h=CMSG_FIRSTHDR(&msg);
+  h->cmsg_len=CMSG_LEN(sizeof(int));
+  h->cmsg_level=SOL_SOCKET;
+  h->cmsg_type=SCM_RIGHTS;
+  *((int*)CMSG_DATA(h))=-1;
+  if (recvmsg(sock,&msg,0)==-1)
+    return -1;
+  h=CMSG_FIRSTHDR(&msg);
+  if (!h || h->cmsg_len!=CMSG_LEN(sizeof(int)) || h->cmsg_level!=SOL_SOCKET || h->cmsg_type!=SCM_RIGHTS) {
+#ifdef EPROTO
+    errno=EPROTO;
+#else
+    errno=EINVAL;
+#endif
+    return -1;
+  }
+  return *((int*)CMSG_DATA(h));
+}

test/fdpassing.c

@@ -0,0 +1,39 @@
+#include <unistd.h>
+#include "io.h"
+#include "buffer.h"
+
+void child(int64 fd) {
+  int64 x=io_receivefd(fd);
+  char buf[8192];
+  int i;
+  if (x==-1) {
+    buffer_putsflush(buffer_2,"fd passing failed!\n");
+    exit(1);
+  }
+  i=read(x,buf,sizeof(buf));
+  write(1,buf,i);
+  io_close(x);
+}
+
+void father(int64 fd) {
+  int64 x;
+  if (io_readfile(&x,"/etc/resolv.conf"))
+    io_passfd(fd,x);
+}
+
+main() {
+  int64 sp[2];
+  if (io_socketpair(sp)==-1) return 1;
+  switch (fork()) {
+  case -1: return 1;
+  case 0:	/* child */
+    io_close(sp[0]);
+    child(sp[1]);
+    break;
+  default:
+    io_close(sp[1]);
+    father(sp[0]);
+    break;
+  }
+  return 0;
+}