Udevstart & udevtrigger

Udevstart & udevtrigger

[Francesco RUNDO]

Hi,

My name is Francesco Rundo and I work porting Linux (kernel, device 
drivers, etc..) for embedded system.

I've a question about udev, in particular way, I need to get some info 
about udevstart and udevtrigger.

In order to improve the boot speed, I've removed in my udev init scripts 
the tool udevstart. Basically, in my udev init scripts (which start 
firstly in the user space boot sequence) there are in order:
1) some operation on /dev  with manually creation of some  devices;
2) udevstart call;
3) starting of udevd;
4) udevtrigger call;
5) udevsettle call;
After that, the common services will be initialized: ssh, D-bus, HAL, 
Lirc, etc...;

I've noted that this sequence is used in different Linux distribution 
for embedded system.

As far as I know, the tool "udevstart" has the target to populate 
initial device directoty (/dev). It walks trough the sysfs device tree 
and calls udev (daemon) to create the nodes for every valid device 
found. It is used to fill the initial empty device directory with nodes 
for all devices currently available. Is it right ?

Now, I know that "udevtrigger"  replies the uevents generated by system 
coldplug of the devices (passing the info to the udev daemon) while 
udevsettle waits watching the udev event queue and exits if all current 
events are handled. Is it right ?

By taking into account what above mentioned, I've removed from udev 
starting script the tool "udevstart" which needs a lot of time to 
populate the device (In my kernel config, I've a lot of device included 
in the kernel ) and I've managed udev only with udevtrigger and 
udevsettle. In this way, the device creation under /dev will be made by 
udevtrigger. I've saved 3/4 sec of boot time!!

Finally, I've to say that in some web site I've noted that some Linux 
distribution were using this approach. Also the initNG project suggests 
to remove udevstart using only udevtrigger & udevsettle. Please, see 
http://www.initng.org/wiki/udevstart for more detail.

Now the question is:
Is it right to remove udevstart using only udevtrigger ?
Are there some funcionality-restrictions in the udev if I don't use 
udevstart ?
Is it true that starting from udev-117 udevstart will not be delivered ?
In my distribution, we are aligned to udev-116

Thanks in advance for your support.

Best Regards,
--
Francesco Rundo

Re: Udevstart & udevtrigger

[Kay Sievers]

On Mon, Sep 1, 2008 at 16:44, Francesco RUNDO <francesco.rundo@st.com> wrote:
> My name is Francesco Rundo and I work porting Linux (kernel, device drivers,
> etc..) for embedded system.
>
> I've a question about udev, in particular way, I need to get some info about
> udevstart and udevtrigger.
>
> In order to improve the boot speed, I've removed in my udev init scripts the
> tool udevstart. Basically, in my udev init scripts (which start firstly in
> the user space boot sequence) there are in order:
> 1) some operation on /dev  with manually creation of some  devices;
> 2) udevstart call;
> 3) starting of udevd;
> 4) udevtrigger call;
> 5) udevsettle call;
> After that, the common services will be initialized: ssh, D-bus, HAL, Lirc,
> etc...;
>
> I've noted that this sequence is used in different Linux distribution for
> embedded system.
>
> As far as I know, the tool "udevstart" has the target to populate initial
> device directoty (/dev). It walks trough the sysfs device tree and calls
> udev (daemon) to create the nodes for every valid device found. It is used
> to fill the initial empty device directory with nodes for all devices
> currently available. Is it right ?
>
> Now, I know that "udevtrigger"  replies the uevents generated by system
> coldplug of the devices (passing the info to the udev daemon) while
> udevsettle waits watching the udev event queue and exits if all current
> events are handled. Is it right ?
>
> By taking into account what above mentioned, I've removed from udev starting
> script the tool "udevstart" which needs a lot of time to populate the device
> (In my kernel config, I've a lot of device included in the kernel ) and I've
> managed udev only with udevtrigger and udevsettle. In this way, the device
> creation under /dev will be made by udevtrigger. I've saved 3/4 sec of boot
> time!!
>
> Finally, I've to say that in some web site I've noted that some Linux
> distribution were using this approach. Also the initNG project suggests to
> remove udevstart using only udevtrigger & udevsettle. Please, see
> http://www.initng.org/wiki/udevstart for more detail.
>
> Now the question is:
> Is it right to remove udevstart using only udevtrigger ?
> Are there some funcionality-restrictions in the udev if I don't use
> udevstart ?
> Is it true that starting from udev-117 udevstart will not be delivered ?
> In my distribution, we are aligned to udev-116

Udevstart is obsolete and does not exist anymore. It was replaced, and
is not installed since udev 082:
  http://git.kernel.org/?p=linux/hotplug/udev.git;a=commit;hÂ33b59baaabe55a8f99dc37c4ee9011b85f8917

Kay