[patch] udevd - switch socket path to abstract namespace

[Kay Sievers <kay.sievers@vrfy.org>]

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As Chris Friesen <chris_friesen@sympatico.ca> suggested, here we switch
the unix domains socket path to abstract namespace and get rid of the
socket file in the filesystem.

Hey, this was new to me today. So here a few words:
  Linux supports a abstract namespace for sockets. We don't need a
  physical file on the filesystem but only a unique string magically
  starting with the '\0' character.

  strace with real file:
    connect(3, {sa_family=AF_UNIX, path="/udev/.udevd.sock"}, 110)

  strace with abstract namespace:
    connect(3, {sa_family=AF_UNIX, path=@udevd}, 110)


thanks,
Kay

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===== Makefile 1.102 vs edited =====
--- 1.102/Makefile	Wed Feb  4 01:56:10 2004
+++ edited/Makefile	Thu Feb  5 01:41:19 2004
@@ -241,7 +241,6 @@
 	@echo \#define UDEV_PERMISSION_FILE	\"$(configdir)\udev.permissions\" >> $@
 	@echo \#define UDEV_BIN		\"$(DESTDIR)$(sbindir)/udev\" >> $@
 	@echo \#define UDEVD_BIN	\"$(DESTDIR)$(sbindir)/udevd\" >> $@
-	@echo \#define UDEVD_SOCK	\"$(udevdir)/\.udevd.sock\" >> $@
 	@echo \#define UDEVD_LOCK	\"$(udevdir)/\.udevd.lock\" >> $@
 
 # config files automatically generated
===== udevd.c 1.11 vs edited =====
--- 1.11/udevd.c	Thu Feb  5 01:40:44 2004
+++ edited/udevd.c	Thu Feb  5 01:42:59 2004
@@ -325,7 +325,6 @@
 		case SIGINT:
 		case SIGTERM:
 			unlink(UDEVD_LOCK);
-			unlink(UDEVD_SOCK);
 			exit(20 + signum);
 			break;
 		default:
@@ -378,9 +377,9 @@
 
 	memset(&saddr, 0x00, sizeof(saddr));
 	saddr.sun_family = AF_LOCAL;
-	strcpy(saddr.sun_path, UDEVD_SOCK);
+	/* use abstract namespace for socket path */
+	strcpy(&saddr.sun_path[1], UDEVD_SOCK_PATH);
 
-	unlink(UDEVD_SOCK);
 	ssock = socket(AF_LOCAL, SOCK_STREAM, 0);
 	if (ssock == -1) {
 		dbg("error getting socket");
@@ -426,6 +425,5 @@
 	}
 exit:
 	close(ssock);
-	unlink(UDEVD_SOCK);
 	exit(1);
 }
===== udevd.h 1.6 vs edited =====
--- 1.6/udevd.h	Mon Feb  2 03:40:48 2004
+++ edited/udevd.h	Thu Feb  5 01:41:33 2004
@@ -27,6 +27,7 @@
 #define UDEV_MAGIC			"udevd_" UDEV_VERSION
 #define EVENT_TIMEOUT_SEC		5
 #define UDEVSEND_CONNECT_RETRY		20 /* x 100 millisec */
+#define UDEVD_SOCK_PATH			"udevd"
 
 struct hotplug_msg {
 	char magic[20];
===== udevsend.c 1.15 vs edited =====
--- 1.15/udevsend.c	Thu Feb  5 01:40:44 2004
+++ edited/udevsend.c	Thu Feb  5 01:41:47 2004
@@ -161,7 +161,8 @@
 
 	memset(&saddr, 0x00, sizeof(saddr));
 	saddr.sun_family = AF_LOCAL;
-	strcpy(saddr.sun_path, UDEVD_SOCK);
+	/* use abstract namespace for socket path */
+	strcpy(&saddr.sun_path[1], UDEVD_SOCK_PATH);
 
 	/* try to connect, if it fails start daemon */
 	retval = connect(sock, (struct sockaddr *) &saddr, sizeof(saddr));