>> On Tue, 17 June 2008 12:55:31 -0700, Tim Bird wrote:
You will be able to open a character device file as soon as cdev_init()
finished... when the Big Kernel Lock is not being taken around
file_operations.open() anymore.
On Tue, 17 Jun 2008 11:28:29 -0700, Tim Bird wrote:
| One technique
| that we are forward-porting from an old kernel (and that I thought I
| might work on mainlining) is to compile modules statically into the
| kernel, but defer their initialization until after boot time.
...
| One of the main sub-systems that we defer initialization of this
| way is USB, and this saves quite a bit of time. (Of course the
| same, or slightly more CPU cycles are eventually used during
| bootup time. But this lets us get to user space quicker so we
| can start user-visible applications faster.)
What if you don't defer module initialization, but merely device probing?
$ ls /sys/bus/*/drivers_autoprobe
/sys/bus/acpi/drivers_autoprobe
/sys/bus/firewire/drivers_autoprobe
/sys/bus/i2c/drivers_autoprobe
/sys/bus/ide/drivers_autoprobe
/sys/bus/pci/drivers_autoprobe
/sys/bus/pci_express/drivers_autoprobe
/sys/bus/platform/drivers_autoprobe
/sys/bus/pnp/drivers_autoprobe
/sys/bus/scsi/drivers_autoprobe
/sys/bus/serio/drivers_autoprobe
/sys/bus/usb/drivers_autoprobe
If you set /sys/bus/foo/drivers_autoprobe to 0 (default is 1), then a
/sys/bus/foo/drivers/bar will not be bound to devices. You can trigger
driver--device binding later per device by writing a device's bus ID
into /sys/bus/foo/drivers/bar/bind, or by writing into
/sys/bus/foo/drivers_probe (I guess; I only used the per-device way so far).
Now, since you want to do this with statically linked drivers, i.e. need
to prevent probing before userspace and sysfs are up and running, you
probably need to modify the bus types or/and the driver core so that the
the less vital buses have drivers_autoprobe off by default.
On the other hand, maybe you want to have probes of some PCI drivers
executed but not the probes of some other PCI drivers; uhci_hcd for
example. I guess you could achieve that by modifying
drivers/pci/pci-driver.c::pci_bus_match(). E.g. add a sysfs attribute
to pci-driver.c which, as long as containing its initial value, lets
bus_match skip certain unwanted drivers (or match only whitelisted
drivers). Later, userspace writes into the extra sysfs attribute and
into the standard driver core sysfs attributes to trigger the deferred
driver probes.
--
Stefan Richter
-=====-==--- -==- =--=-
http://arcgraph.de/sr/
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