which devices will be displayed in hal-device-manager

[Dan Williams]

On Wed, 7 Sep 2005 WMWu at Winbond.com.tw wrote:
> Dear All:
> 
> Which device will be displayed in hal-device-manager? My OS is Fedora
> Core 3, version of hal-device-manager is 0.4.0

Hi,

hal-device-manager will display any device that HAL itself knows about.  Another 
way to see all the devices HAL knows about is the 'lshal' command, which is 
similar to the standard 'lspci' command.

HAL finds devices (and information about those devices) in a number of ways:

1) Reading various entries in /proc, for example mountpoints and other things.  
Some device information is found here, but this is historical and most 
everything for hardware devices should be in /sys already.

2) Reading stuff in /sys.  This is _really_ important, and is highly 
device-driver dependent.  If a device driver doesn't expose its information via 
the sysfs filesystem in /sys, then the driver is considered broken and buggy 
anyway.  For example, network device drivers MUST use the SET_NETDEV_DEV() call 
to make the link from /sys/class/net/eth[x]/device to their device's entry in 
/sys/bus/pci or /sys/bus/pcmcia.  If you're writing a driver, make sure that it 
follows the correct rules for exposing its details via sysfs.  HAL will then be 
able to see all its details.  The Intel ipw2200 driver is a great example here.

3) .fdi files.  When HAL can't determine details about a particular device from 
the information in /proc, /sys, or other places, it looks at .fdi files and 
merges the properties listed in those files onto the device node in the HAL 
device list.  This allows for detection of certain digital cameras and other 
devices for which there is not enough identifying information.

4) Reading information from the device (?)  I'm not sure if this is still done 
for things like file systems, but HAL used to try to read some information from 
various devices, like disks, to figure out what filesystem type they had, or 
whether they were encrypted, etc.

If you're wondering why a device doesn't show up in HAL, first make sure that it 
is listed in sysfs (/sys).  Each device will usually have at least two entries, 
for example /sys/class/net/eth0 (which is the capability of the device, and is 
driver-created) and /sys/devices/pci0000:00/0000:00:1e.0/0000:02:00.0 (which is 
from the Linux kernel PCI drivers).  The driver-created entries, ie 
/sys/class/net/eth0 needs to have a device link pointing to the second entry 
here, the PCI one.  That's created in the driver by SET_NETDEV_DEV() for 
example.  Other types of devices, like USB, IDE devices, etc, have similar 
mechanisms for populating their sysfs directories.

In general, the earlier the kernel is in the 2.6 series, the worse the driver 
support for HAL is.  You should really only use HAL with 2.6.8 and later 
kernels, and each kernel release after 2.6.8 gets better driver support for 
sysfs, and therefore also for HAL.

David Z will probably have more to say, but hope this helps.  Was there any 
paritcular device that didn't show up that you were wondering about?

Dan