MAJOR: listener: support inheriting a listening fd from the parent
Using the address syntax "fd@<num>", a listener may inherit a file
descriptor that the caller process has already bound and passed as
this number. The fd's socket family is detected using getsockname(),
and the usual initialization is performed through the existing code
for that family, but the socket creation is skipped.
Whether the parent has performed the listen() call or not is not
important as this is detected.
For UNIX sockets, we immediately clear the path after preparing a
socket so that we never remove it in case an abort would happen due
to a late error during startup.
diff --git a/src/proto_uxst.c b/src/proto_uxst.c
index 3263ea4..85eb3ee 100644
--- a/src/proto_uxst.c
+++ b/src/proto_uxst.c
@@ -111,6 +111,10 @@
struct sockaddr_un addr;
int sock, ret;
+ /* if the path was cleared, we do nothing */
+ if (!*path)
+ return;
+
/* We might have been chrooted, so we may not be able to access the
* socket. In order to avoid bothering the other end, we connect with a
* wrong protocol, namely SOCK_DGRAM. The return code from connect()
@@ -157,6 +161,8 @@
struct sockaddr_un addr;
const char *msg = NULL;
const char *path;
+ int ext, ready;
+ socklen_t ready_len;
int ret;
@@ -169,6 +175,16 @@
path = ((struct sockaddr_un *)&listener->addr)->sun_path;
+ /* if the listener already has an fd assigned, then we were offered the
+ * fd by an external process (most likely the parent), and we don't want
+ * to create a new socket. However we still want to set a few flags on
+ * the socket.
+ */
+ fd = listener->fd;
+ ext = (fd >= 0);
+ if (ext)
+ goto fd_ready;
+
/* 1. create socket names */
if (!path[0]) {
msg = "Invalid empty name for a UNIX socket";
@@ -215,6 +231,7 @@
goto err_unlink_back;
}
+ fd_ready:
if (fd >= global.maxsock) {
msg = "socket(): not enough free sockets, raise -n argument";
goto err_unlink_temp;
@@ -225,7 +242,7 @@
goto err_unlink_temp;
}
- if (bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
+ if (!ext && bind(fd, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
/* note that bind() creates the socket <tempname> on the file system */
msg = "cannot bind UNIX socket";
goto err_unlink_temp;
@@ -236,14 +253,21 @@
* While it is known not to be portable on every OS, it's still useful
* where it works.
*/
- if (((listener->bind_conf->ux.uid != -1 || listener->bind_conf->ux.gid != -1) &&
- (chown(tempname, listener->bind_conf->ux.uid, listener->bind_conf->ux.gid) == -1)) ||
- (listener->bind_conf->ux.mode != 0 && chmod(tempname, listener->bind_conf->ux.mode) == -1)) {
+ if (!ext &&
+ (((listener->bind_conf->ux.uid != -1 || listener->bind_conf->ux.gid != -1) &&
+ (chown(tempname, listener->bind_conf->ux.uid, listener->bind_conf->ux.gid) == -1)) ||
+ (listener->bind_conf->ux.mode != 0 && chmod(tempname, listener->bind_conf->ux.mode) == -1))) {
msg = "cannot change UNIX socket ownership";
goto err_unlink_temp;
}
- if (listen(fd, listener->backlog ? listener->backlog : listener->maxconn) < 0) {
+ ready = 0;
+ ready_len = sizeof(ready);
+ if (getsockopt(fd, SOL_SOCKET, SO_ACCEPTCONN, &ready, &ready_len) == -1)
+ ready = 0;
+
+ if (!(ext && ready) && /* only listen if not already done by external process */
+ listen(fd, listener->backlog ? listener->backlog : listener->maxconn) < 0) {
msg = "cannot listen to UNIX socket";
goto err_unlink_temp;
}
@@ -253,13 +277,19 @@
* fear loosing the socket <path> because we have a copy of it in
* backname.
*/
- if (rename(tempname, path) < 0) {
+ if (!ext && rename(tempname, path) < 0) {
msg = "cannot switch final and temporary UNIX sockets";
goto err_rename;
}
- /* 6. cleanup */
- unlink(backname); /* no need to keep this one either */
+ /* 6. cleanup. If we're bound to an fd inherited from the parent, we
+ * want to ensure that destroy_uxst_socket() will never remove the
+ * path, and for this we simply clear the path to the socket.
+ */
+ if (!ext)
+ unlink(backname);
+ else
+ ((struct sockaddr_un *)&listener->addr)->sun_path[0] = 0;
/* the socket is now listening */
listener->fd = fd;
@@ -275,13 +305,19 @@
if (ret < 0 && errno == ENOENT)
unlink(path);
err_unlink_temp:
- unlink(tempname);
+ if (!ext)
+ unlink(tempname);
close(fd);
err_unlink_back:
- unlink(backname);
+ if (!ext)
+ unlink(backname);
err_return:
- if (msg && errlen)
- snprintf(errmsg, errlen, "%s [%s]", msg, path);
+ if (msg && errlen) {
+ if (!ext)
+ snprintf(errmsg, errlen, "%s [%s]", msg, path);
+ else
+ snprintf(errmsg, errlen, "%s [fd %d]", msg, fd);
+ }
return ERR_FATAL | ERR_ALERT;
}