D-BUS patch for udev-008

Hi,

Attached is a patch against udev-008 to send out a D-BUS message when a device node is added or removed.

Using D-BUS lingo, udev acquires the org.kernel.udev service and sends out a NodeCreated or NodeDeleted signal on the org.kernel.udev.NodeMonitor interface. Each signal carries two
parameters: the node in question and the corresponding sysfs path.

[Note: the D-BUS concepts of service, interface, object can be a bit confusing at first glance]

An example program listening for these messages looks like this

#!/usr/bin/python

import dbus
import gtk

def udev_signal_received(dbus_iface, member, service, object_path, message):
[filename, sysfs_path] = message.get_args_list()
if member=='NodeCreated':
print 'Node %s created for %s'%(filename, sysfs_path)
elif member=='NodeDeleted':
print 'Node %s deleted for %s'%(filename, sysfs_path)

def main():
bus = dbus.Bus(dbus.Bus.TYPE_SYSTEM) bus.add_signal_receiver(udev_signal_received,
'org.kernel.udev.NodeMonitor', # interface
'org.kernel.udev', # service
'/org/kernel/udev/NodeMonitor') # object

gtk.mainloop()

if __name__ == '__main__':

    main()

and this is the output when hot-plugging some usb-storage.

[david@laptop udev-008]$ ~/node_monitor.py
Node /udev/sda created for /block/sda
Node /udev/sda1 created for /block/sda/sda1
Node /udev/sda1 deleted for /block/sda/sda1
Node /udev/sda deleted for /block/sda

The patch requires D-BUS 0.20 or later while the python example program requires D-BUS from CVS as I only recently applied a patch against the python bindings.

Cheers,
David

diff -Nru ../orig/udev-008/Makefile ./Makefile
@@ -20,6 +20,10 @@
 # Leave this set to `false' for production use.
 DEBUG = false
 
+# Set the following to `true' to make udev emit a D-BUS signal when a
+# new node is created.
+USE_DBUS = true
+
 
 ROOT =		udev
 VERSION =	008

@@ -34,6 +38,7 @@
 sbindir =	${exec_prefix}/sbin
 mandir =	${prefix}/usr/share/man
 hotplugdir =	${etcdir}/hotplug.d/default
+dbusdir =	${etcdir}/dbus-1/system.d
 configdir =	${etcdir}/udev/
 srcdir = .
 

@@ -133,6 +138,13 @@
 	LDFLAGS = --static 
 endif
 
+ifeq ($(USE_DBUS), true)
+	CFLAGS += -DUSE_DBUS
+	CFLAGS += $(shell pkg-config --cflags dbus-1)
+	LIB_OBJS += $(shell pkg-config --libs-only-l dbus-1)
+endif
+
+
 all: $(ROOT)
 
 $(ROOT): $(LIBC)

@@ -225,7 +237,20 @@
 	@echo "Built $(RELEASE_NAME).tar.gz"
 
 
-install: all
+ifeq ($(USE_DBUS), true)
+install-dbus-policy:
+	$(INSTALL) -d $(DESTDIR)$(dbusdir)
+	$(INSTALL_DATA) udev_sysbus_policy.conf $(DESTDIR)$(dbusdir)
+uninstall-dbus-policy:
+	- rm $(DESTDIR)$(dbusdir)/udev_sysbus_policy.conf
+else
+install-dbus-policy:
+	-
+uninstall-dbus-policy:
+	-
+endif
+
+install: install-dbus-policy all
 	$(INSTALL) -d $(DESTDIR)$(udevdir)
 	$(INSTALL) -d $(DESTDIR)$(configdir)
 	$(INSTALL) -d $(DESTDIR)$(hotplugdir)

@@ -237,7 +262,7 @@
 	- rm -f $(DESTDIR)$(hotplugdir)/udev.hotplug
 	- ln -s $(sbindir)/$(ROOT) $(DESTDIR)$(hotplugdir)/udev.hotplug
 
-uninstall:
+uninstall: uninstall-dbus-policy
 	- rm $(hotplugdir)/udev.hotplug
 	- rm $(configdir)/udev.permissions
 	- rm $(configdir)/udev.rules

diff -Nru ../orig/udev-008/TODO ./TODO
@@ -21,7 +21,6 @@
   will have an upgrade path.
 - do early boot logic (putting udev into initramfs, handle pivot-root,
   etc.)
-- add hooks to call D-BUS when new node is created or removed
 - lots of other stuff...
 - actually use the BUS= value to determine where the LABEL rule should look
   (right now it's ignored, and we only look in the current sysfs directory.)

diff -Nru ../orig/udev-008/udev.h ./udev.h
@@ -92,4 +92,13 @@
 extern char udev_rules_filename[PATH_MAX+NAME_MAX];
 extern char default_mode_str[NAME_MAX];
 
+#ifdef USE_DBUS
+
+#define DBUS_API_SUBJECT_TO_CHANGE
+#include <dbus/dbus.h>
+
+extern DBusConnection* sysbus_connection;
+
+#endif /* USE_DBUS */
+
 #endif

diff -Nru ../orig/udev-008/udev_sysbus_policy.conf ./udev_sysbus_policy.conf
@@ -0,0 +1,23 @@
+<!DOCTYPE busconfig PUBLIC
+ "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
+ "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+<busconfig>
+
+  <!-- This configuration file specifies the required security policies
+       for udev to work. -->
+
+  <!-- Only root can own the udev service and only root can use the
+       org.kernel.udev.NodeMonitor interface to send signals -->
+  <policy user="root">
+    <allow own="org.kernel.udev"/>
+
+    <allow send_interface="org.kernel.udev.NodeMonitor"/>
+  </policy>
+
+  <!-- Allow anyone to listen to the org.kernel.udev.NodeMonitor interface 
+       for messages send from the owner of the org.kernel.udev service -->
+  <policy context="default">
+    <allow receive_interface="org.kernel.udev.NodeMonitor"/>
+  </policy>
+</busconfig>
+

Rock!

Good job, David.

Rob Love

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Very nice. I've applied your patch, and then made the following changes:
- fixed the formatting to use tabs instead of spaces
- removed all of the #ifdef USE_DBUS statments out of the code (I've been writing kernel code too long, #ifdef within .c files looks ugly to me...) and created a new file udev_dbus.c to hold these functions.
- changed the Makefile variable to DBUS instead of USE_DBUS
- turned the default option to not build the DBUS support as I can't get it to link properly on a number of different OSs.

How did you test this? I get lots of errors at link time using a Fedora 1 machine. And I can't even build DBUS on an old Red Hat 7.3 box due to automake issues :(

I've checked all of this into the bk tree if anyone else wants to play with it.

thanks,

greg k-h

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Many thanks for this.

I'm using Fedora 1 with D-BUS from CVS installed in /usr/local. I do get a few message from the linker because of static linking, see below, but it does link. What's the reason for linking statically?

Btw, Fedora 1 ships with D-BUS 0.13 which is way different from D-BUS in CVS, so you might need to set PKG_CONFIG_PATH to point to the correct dbus-1.pc and install udev_sysbus_policy.conf into the proper location.

Oh, and even though you have done this, you might still link with the old D-BUS because I made a mistake in the Makefile. You need to change

  LIB_OBJS += $(shell pkg-config --libs-only-l dbus-1)

to something like

  LDFLAGS += $(shell pkg-config --libs dbus-1)

yes? (I was tweaking the Makefile quite a lot myself; sorry about that)

I've also found a problem with my patch: There's an issue where when two instances of udev is running at the same time (processing /block/sda and /block/sda/sda1 when plugging in usb-storage).

One of the copies become a secondary owner of the org.kernel.udev service and this means that the emitted D-BUS signal doesn't appear to come from the owner of that service as I thought it would. I'm not sure if this is the intended behavior of D-BUS, it might be..

The only reason it works in python is that, uhm, the python bindings are a bit broken. It only works in C if you ignore filtering on service owner.

Cheers,
David

[david@laptop udev-008]$ touch udev.c
[david@laptop udev-008]$ make
gcc -pipe -Wall -Wshadow -Wstrict-prototypes -Wmissing-prototypes
-Wmissing-declarations -Os -fomit-frame-pointer -D_GNU_SOURCE
-I/usr/lib/gcc-lib/i386-redhat-linux/3.3.2/include -DUSE_DBUS
-I/usr/local/include/dbus-1.0 -I/usr/local/lib/dbus-1.0/include -c
-o udev.o udev.c
udev.c:75: warning: function declaration isn't a prototype
udev.c:85: warning: function declaration isn't a prototype
gcc --static -o udev udev.o udev_config.o udev-add.o udev-remove.o
udevdb.o logging.o namedev.o namedev_parse.o libsysfs/sysfs_bus.o
libsysfs/sysfs_class.o libsysfs/sysfs_device.o libsysfs/sysfs_dir.o
libsysfs/sysfs_driver.o libsysfs/sysfs_utils.o libsysfs/dlist.o
tdb/tdb.o tdb/spinlock.o -lc -ldbus-1
udev-add.o(.text+0x30d): In function `create_node':
: warning: Using 'getgrnam' in statically linked applications requires
at runtime the shared libraries from the glibc version used for linking
udev-add.o(.text+0x2cb): In function `create_node':
: warning: Using 'getpwnam' in statically linked applications requires
at runtime the shared libraries from the glibc version used for linking
/usr/local/lib/libdbus-1.a(dbus-sysdeps.o)(.text+0x14e0): In function
`fill_user_info':
/home/david/xdg-hacking/dbus/dbus/dbus-sysdeps.c:1504: warning: Using
'getgrouplist' in statically linked applications requires at runtime the
shared libraries from the glibc version used for linking
/usr/local/lib/libdbus-1.a(dbus-sysdeps.o)(.text+0x1482):/home/david/xdg-hacking/dbus/dbus/dbus-sysdeps.c:1467: warning: Using 'getpwuid' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking /usr/local/lib/libdbus-1.a(dbus-sysdeps.o)(.text+0x6e3): In function
`_dbus_connect_tcp_socket':
/home/david/xdg-hacking/dbus/dbus/dbus-sysdeps.c:617: warning: Using
'gethostbyname' in statically linked applications requires at runtime
the shared libraries from the glibc version used for linking
strip -s --remove-section=.note --remove-section=.comment udev

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udev will need to be able to go into initramfs for early boot. We will not have access to glibc at that time (well, we could, but it would be a lot of overkill...)

Ok, thanks. I'll go try that later.

Thanks, I've applied this to the repo.

Hm, eventually udev will turn into a daemon, and only have 1 version running at a time. The events will be queued up into the udev daemon so you will not have this problem.

thanks,

greg k-h

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