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Re: [cdi-devel] Proposed Dynamic Driver Loading System

On Sun, Jan 3, 2010 at 9:38 AM, Kevin Wolf <kevin@xxxxxxxxxx> wrote:
> On Sun, Jan 03, 2010 at 09:23:30AM +1000, Matthew Iselin wrote:
>> On Sun, Jan 3, 2010 at 3:13 AM, Rich Edelman <redelman@xxxxxxxxx> wrote:
>> > On Sat, Jan 2, 2010 at 5:46 AM, Kevin Wolf <kevin@xxxxxxxxxx> wrote:
>> >> On Sat, Jan 02, 2010 at 04:58:39PM +1000, Matthew Iselin wrote:
>> >>> The idea is that the OS stores a map of device identifiers (at this stage the
>> >>> proposal considers the use of PCI vendor and device codes) which detail the
>> >>> name of a driver which is to be loaded if the given device is detected. This
>> >>> list may be OS-specific, or there may be a generic list provided as part of
>> >>> CDI. Either way, the OS is open to interpret the driver name as it sees fit:
>> >>> for example, appending ".o" in the case of Pedigree.
>> >>>
>> >>> This map might look something like this:
>> >>>
>> >>> /** OS-specific map of PCI identifiers -> driver names */
>> >>>
>> >>> struct cdi_os_pci_driver_map = {
>> >>>     0x8086, 0x1230, "piix", // Vendor, Device, Driver name
>> >>>     ...
>> >>> };
>> >>
>> >> This would be an additional top-level C file, right? I don't think it's
>> >> a good idea to manually create it and keep it in sync (especially
>> >> considering that many OSes don't use all drivers), but generating such a
>> >> file looks fine to me.
>> >
>> > I also agree that such a file should be generated. It'd not be too
>> > hard to generate this list just from the drivers that were compiled,
>> > rather than containing all the drivers.
>> A simple <your scripting language here> script could be added and
>> called to update the list during the build of CDI.
> Actually I think C would be the right tool. Link all object files in the whole
> tree together and add a small main() function that enumerates all the drivers
> in it. All the parsing is done by the compiler.

Hm, good point. A little more complicated, but also comes with the
bonus of needing no new dependency on Perl or Python or <your
scripting language here>.

>> >>> At a time defined by the OS implementing CDI, the list of PCI devices will be
>> >>> iterated, and each device will be checked against the known PCI->driver list.
>> >>> Should a driver be found in this list, the driver will be loaded (if not
>> >>> already) and used to initialise the detected device.
>> >>>
>> >>> Now, this brings up a small tangent: it is my belief that driver loading could
>> >>> be added to the CDI interface, as something like:
>> >>>
>> >>> /* Returns -1 if the driver could not be loaded, zero otherwise */
>> >>> int cdi_load_driver(const char *);
>> >
>> > I think this prototype is all wrong. Whatever it is that wants to load
>> > another driver needs to pass a structure that describes the device a
>> > driver is needed for. Driver's shouldn't be expected to know the name
>> > of the driver they need for another device. Sure, they can get this
>> > from the mapping file discussed previously, but I think that's wrong
>> > as well. Such a file needs to really be internal to the CDI core, and
>> > not something used by the drivers (only contributed to by the
>> > drivers).
>> Yes, this specifically is one thing I was very unsure about when I
>> thought out the initial proposal. The main reason I brought it up was
>> for a situation like this:
>> 1. Plug in a USB device
>> 2. The USB controller driver tells the  OS a new device is plugged in.
>> Now the OS needs to figure out what driver to load for the device.
>> The `cdi_load_driver' function is certainly incorrect here, but some
>> sort of hook in CDI to inform the OS of a new device that has been
>> added would help here.
> Right, we're mostly complete on the device driver side, but the bus
> driver side (providing/removing devices) is completely missing. However,
> we seem to agree that this is the right interface for loading drivers,
> so maybe the next step would be specifying the bus driver interface.

And so the fun begins ;)

> Actually, I think's quite boring. Some cdi_provide_device(struct
> cdi_bus_addr*), a function for removing (probably takes the cdi_bus_addr
> again?) and we're done.

Right, this is kind of what I was thinking of when I considered the
feedback given to the original proposal.

The question is: can a USB device be fully... explained, I guess, in a
cdi_bus_addr? What about Firewire? Max raises an excellent point in
his mail; I don't understand cdi_bus_addr enough yet to comment on
whether or not it suffices for these purposes. If a cdi_bus_addr
struct can describe the wider range of potential devices (and
therefore drivers), this will not be a problem.

> Finding good names might be the most difficult thing in it. ;-)

One can only hope ;)

Also, apologies for any duplicate emails... My connection is quite
temperamental and may tell me the mail did not get sent, when in fact
it did, so I re-send the mail. Just ignore multiple copies of the same