ogasawara@osdl.org
9a52390cfe
I noticed a comment in namedev.c which stated "Figure out where the device symlink is at. For char devices this will always be in the class_dev->path. But for block devices, it's different. The main block device will have the device symlink in it's path, but all partitions have the symlink in its parent directory. But we need to watch out for block devices that do not have parents, yet look like a partition (fd0, loop0, etc.). They all do not have a device symlink yet. We do a sit and spin on waiting for them right now, we should possibly have a whitelist for these devices here..." I went ahead and created a whitelist for the block devices that look like partitions (mainly by using devices.txt) and tested for any performance increase that we would see. The whitelist only impacts udevstart time depending on the state of UDEV_NO_SLEEP. Since the list was short, I just did a sequential search and ordered the list in such a way that those block devices which have more /dev entires (ex. loop0, loop1, loop2, etc) appear sooner in the list and will thus be found quicker. I've enclosed the patch and some of the performance results I saw below. Basically, as the number of block devices without device symlinks increased, the use of the whitelist improved udevstart performance compared to just sitting and spinning. I just thought it was interesting and thought I'd share. If you feel the patch is beneficial please consider for merging. Also, if you'd be interested in expanding the whitelist for other devices which are missing device symlinks and seeing if there are added performance increases let me know and I'll do what I can. Thanks, Leann Note: ex. loop represents all the loop devices (i.e. loop0, loop1, loop2, etc) block devices present with whitelist time
udev - a userspace implementation of devfs
For more information on the design, and structure of this project, see the
files in the docs/ directory.
To use:
- You must be running a 2.6 version of the Linux kernel.
- Your 2.6 kernel must have had CONFIG_HOTPLUG enabled when it was built.
- Make sure sysfs is mounted. udev will figure out where sysfs is mounted, but
the traditional place for it is at /sys. You can mount it by hand by running:
mount -t sysfs none /sys
- Make sure you have the latest version of the linux-hotplug scripts. They are
available at linux-hotplug.sf.net or from your local kernel.org mirror at:
kernel.org/pub/linux/utils/kernel/hotplug/
They are required in order for udev to work properly.
If for some reason you do not install the hotplug scripts, you must tell the
kernel to point the hotplug binary at wherever you install udev at. This can
be done by:
echo "/sbin/udev" > /proc/sys/kernel/hotplug
- Build the project:
make
Note:
There are a number of different flags that you can use when building
udev. They are as follows:
prefix
set this to the default root that you want udev to be
installed into. This works just like the 'configure --prefix'
script does. Default value is ''. Only override this if you
really know what you are doing.
USE_KLIBC
if set to 'true', udev is built and linked against the
included version of klibc. Default value is 'false'.
USE_LOG
if set to 'true', udev will emit messages to the syslog when
it creates or removes device nodes. This is helpful to see
what udev is doing. This is enabled by default. Note, if you
are building udev against klibc it is recommended that you
disable this option (due to klibc's syslog implementation.)
DEBUG
if set to 'true', debugging messages will be sent to the syslog
as udev is run. Default value is 'false'.
KERNEL_DIR
If this is not set it will default to /lib/modules/`uname -r`/build
This is used if USE_KLIBC=true to find the kernel include
directory that klibc needs to build against. This must be set
if you are not building udev while running a 2.6 kernel.
So, if you want to build udev using klibc with debugging messages, you
would do:
make USE_KLIBC=true DEBUG=true
- Install the project:
make install
This will put the udev binary in /sbin, create the /udev and /etc/udev
directories, and place the udev configuration files in /etc/udev. You
will probably want to edit the namedev.* files to create custom naming
rules. More info on how the config files are set up are contained in
comments in the files, and is located in the documentation.
- Add and remove devices from the system and marvel as nodes are created
and removed in /udev/ based on the device types.
- If you later get sick of it, uninstall it:
make uninstall
Things are still quite rough, but it should work properly. If nothing
seems to happen, make sure your build worked properly by running the
udev-test.pl script as root in the test/ subdirectory of the udev source
tree.
Development and documentation help is very much appreciated, see the TODO
file for a list of things left to be done.
Any comment/questions/concerns please let me and the other udev developers
know by sending a message to the linux-hotplug-devel mailing list at:
linux-hotplug-devel@lists.sourceforge.net
greg k-h
greg@kroah.com