[PATCH] get_netlink_msg: unable to receive kernel netlink message:

[Matthias Schwarzott <zzam@gentoo.org>]

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Hi there!

Had this Bug-report floating around since some time:
http://bugs.gentoo.org/show_bug.cgi?id=151414

It occurs, when root-partition has no /dev/console, meaning that kernel could 
not open it, and such udevd is started without open filedescriptors 0 1 2.

In that case udevd openes its sockets (netlink and control).
They get fds between 0 and 2.

Later duping /dev/null to 0 1 2 closes the sockets and replaces them 
with /dev/null.

Communicating over socket in main-look then gets that error-messages.


One possible solution is:
Checking at startup of udevd that fd 0 1 2 are open, and if not, connect them 
to /dev/null.
A. For example by explictely checking each fd and dup /dev/null (attached 
patch).
B. By opening /dev/null until open returns 2 meaning fds 0 1 2 are open.
C. Remembering which fd is open, and later only dup/close the ones that were 
open.

But in case C one perhaps has to conditionalize each printf(...) and 
fprintf(2,...) as the sockets are sure not happy about text-messages.


For gentoo-startup, that does work without /dev/console, only udevd has 
problems there, we solved it for now this way in udev-startup script (until 
udevd copes with this itself):

# check if /dev/console exists outside tmpfs
[[ -c /dev/console ]] ; local need_redirect=$?
....
mount /dev
....
mknod /dev/null
mknod /dev/console
...
if [[ ${need_redirect} == 1 ]]; then
	/sbin/udevd --daemon </dev/console >/dev/console 2>/dev/console
else
	/sbin/udevd --daemon
fi


Matthias

-- 
Matthias Schwarzott (zzam)

[-- Attachment #2: udev-104-std_fd_dup_fix.patch --]
[-- Type: text/x-diff, Size: 596 bytes --]

--- udev-104-orig/udevd.c	2007-01-15 14:56:11.000000000 +0100
+++ udev-104/udevd.c	2007-01-29 13:47:56.000000000 +0100
@@ -948,6 +948,21 @@
 	int rc = 1;
 	int maxfd;
 
+	fd = open("/dev/null", O_RDWR);
+	
+	if (fd < 0) {
+		fprintf(stderr, "cannot open /dev/null\n");
+		err("cannot open /dev/null");
+	}
+	if (read(STDIN_FILENO, 0, 0) < 0)
+		dup2(fd, STDIN_FILENO);
+	if (write(STDOUT_FILENO, 0, 0) < 0)
+		dup2(fd, STDOUT_FILENO);
+	if (write(STDERR_FILENO, 0, 0) < 0)
+		dup2(fd, STDERR_FILENO);
+	if (fd > 2)
+		close(fd);
+
 	logging_init("udevd");
 	udev_config_init();
 	selinux_init();

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