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With well defined and kernel-supplied node names, we no longer need
to support a possible stack of conflicting symlinks and node names.
Only symlinks with identical names can be claimed by multiple devices.
This shrinks the former /dev/.udev/names/ significantly.
Also the /dev/{block,char}/MAJ:MIN" links are excluded from the name
stack - they are unique and can not conflict.
With very deeply nested devices, We can not use a single file
name to carry an entire DEVPATH. Use <subsystem>:<sysname> as
the database filename, which should also simplify the handling
of devices moving around, as these values will not change but
still be unique.
For the name stack we use the <maj>:<min> now as the filename.
> On Tue, Aug 18, 2009 at 09:59:56AM -0400, Ric Wheeler wrote:
> The first is that udev grumbles during boot about "file name too long"
> like the following:
>
> Aug 17 06:49:58 megadeth udevd-event[20447]: unable to create db file
> '/dev/.udev/db/\x2fdevices\x2fpci0000:00\x2f0000:00:04.0\x2f0000:17:00.0\x2f0000:18:0a.0\x2f0000:1f:00.0\x2fhost11\x2fport-11:0\x2fexpander-11:0\x2fport-11:0:0\x2fexpander-11:1\x2fport-11:1:0\x2fexpander-11:2\x2fport-11:2:17\x2fexpander-11:3\x2fport-11:3:1\x2fend_device-11:3:1\x2fbsg\x2fend_device-11:3:1':
> File name too long
We must never access random devices in /dev which do not belong to
the event we are handling. Hard-coding /dev/hidrawX, and looping over all
devices is absolutely not acceptable --> hook into hidraw events.
We can not relay on (rather random) properties merged into the parent
device by earlier rules --> use libudev to find the sibling device
with a matching interface.
Libusb does not fit into udev's use case. We never want want to scan
and open() all usb devices in the system, just to find the device
we are already handling the event for --> put all the stupid scanning
into a single function and prepare for a fixed libusb or drop it later.
We need to call ata_id as the default for libata sd* devices. We
want ID_BUS=ata, and the ATA device proeprties, and be independent
of the SCSI emulation with the truncated values. The links
in /dev/disk/by-id/{ata-*,scsi-*} are still the same.
Event processes now get re-used after they handled an event. This reduces
pressure on the CPU significantly because cloned event processes no longer
cause page faults in the main daemon. After the events have settled, the
no longer needed worker processes get killed.
UDev follows the kernel given name, and re-uses the kernel created
device node. If the kernel and spcecified udev rules disagree, the
udev specified node node is created and the kernel-created on is
deleted.
The in-memory rule array of a common desktop distro install took:
1151088 bytes
with the token list:
109232 bytes tokens (6827 * 16 bytes), 71302 bytes buffer
