Hi all,
I was looking at the implementation of the LKM and more precisely of the
kmod subsystem.
The function request_module load a module with the help of a user process.
I agree that it's more secure, more efficient :)
But it's quite annoying. Here is an example : ext3 module request the block
device driver modules. At the boot of a machine, the hotplug (a userspace
programm) will detect an ext3 partition.
It will load the ext3 module, which will load the block device driver module.
Here is a little scheme :
module_load(ext3) module_load(block_device_driver)
| | | USER SPACE
| | |
| | |
-----------------------------------------------------------------------
| | |
| | | KERNEL SPACE
| | |
request_module(block_device_driver) load_module(block_device_driver)
& load_module(ext3)
It's clearly not beautiful :) a lot of switch between user space and kernel
space.
In fact, this subsystem relies on the non stupidity of the administrator
or some user space soft : it's more efficient to load block_device_driver
module first and ext3 module secondly.
I've tried to think at a better implementation but I did not find one. :)
But I think I've found a little "bug".
In fact, the function request_module does not test if the requested_module
is already listed : the user mode helper process is launched in all the
cases.
I think it would be more efficient to test it.
I was a little sceptic by my understanding of the system so I made some
tests to be sure.
Tests
------
I've replace the /sbin/modprobe binary with a little script which prints
a dummy message in a file.
And I've written a module with the following init function :
int __init loading(void)
{
request_module(smbfs);
return 0;
}
1st test
--------
At first, I load the module with insmod.
My modprobe script is effectively launched (creation of a file).
2nd test
--------
I load smbfs (with the real modprobe binary) and I re load the module.
My modprobe script is launched again.
There are 2 solutions :
_ searching the name in module_list
_ or adding a hash list of modules (to improve the looking of
a module)
Which one is the best ?
And is my understandfing good too ?:)
Thanks
--
tyler
tyler@xxxxxxxx
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