Re: USB bulk transfert from GRUB ?

[Nicolas de Pesloüan]

Le 26/12/2010 13:05, Vladimir 'φ-coder/phcoder' Serbinenko a écrit :

> > I think we can reasonably discover the particular switchable and
> > bootable device a grub-mkconfig time and put the single (vendor-id,
> > device-id, end-point-number, switch-string) in grub.cfg :
> >
> > usb_bulk_write --vendor 0x0af0 --device 0x7501 --endpoint 0 \
> >      --string
> > 0x55534243785634120100000080000601000000000000000000000000000000
> >
> > (example from /etc/usb_modeswitch.d/0af0:7501)
> How exactly do we do it on mkconfig time? What prevents doing it on runtime?

Thinking about it for long, I don't really know which of mkconfig time or 
runtime is the best.

##### mkconfig time #####

I originally thought I would simply add the required switch command into some menuentry in grub.cfg, 
to switch the device, if the volume is located on a well known switchable device.

In prepare_grub_to_access_device() (in /usr/lib/grub/grub-mkconfig_lib), one can add some commands 
(or options to the search command), to switch the device, if the device that hold the boot volume is 
known to be switchable.

I also thought grub-probe might be enhanced (in probe() function) to query the vendor/product id of 
the underlying physical device and look for those vendor/product id in the usb_modeswitch database, 
then report "switchable" as an abstraction.

But, having a closer look at it, I now understand that this would require crossing all the levels 
down to the physical device, which might be a little tricky. (I don't know, may be it is something 
already done somewhere).

##### runtime #####

Nothing prevent selecting the right switch string and end-point at run time, based on the 
vendor/product id and the usb_modeswitch database. This is exactly what usb_modeswitch do. It might 
even be possible to share part of the code between usb_modeswitch and the GRUB counterpart, only 
changing the function calls from libusb to GRUB usb library. (Of course, the license for 
usb_modeswitch should be double checked before).

But we need to have a way to decide which device to switch and which not to switch, based on whether 
we need this particular device to boot. Again, switching a device early might lead to some problem 
later, in the operating system. For example, if we boot Windows from GRUB, having the Option device 
connected (and switched by GRUB), then Windows won't have access to the driver (which is located on 
the virtual CD), preventing the installation of this driver.

But here, we face a chicken and egg problem: In order to know a given device should be switched, we 
need to search the UUID (ou label or whatever) in this device.

##########

May be I walk the wrong way. It might be enough to add "usb_modeswitch" to GRUB_PRELOAD_MODULES in 
/etc/default/grub if one plan to boot from a switchable device, and let the "usb_modeswitch" module 
switch all known devices at runtime. This assume people able to build such a boot environment are 
not in trouble with installing the Windows driver by hand if they use Windows...

Or may be we can just add the switch feature in all menuentry except those clearly linked to Windows 
in 30_os-prober, assuming that switching early cannot cause trouble to any OS except Windows.

I don't know...

        Nicolas.