On Wed, 9 Dec 2009, Andreas Kemnade wrote: > On Sat, 5 Dec 2009 15:34:07 -0500 (EST) > Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > > > The following patch solves the problem for the BIOS. I am able to load > > > a kernel and an initrd with it correctly. Of course, it breaks everything > > > else but it can be considered as a proof of concept. I can boot from my > > > my g_file_storage cdrom drive with it on that thinkpad X31, on a mainboard with award > > > bios (with an AMD Geode 1700+ on it) and also on an INTEL D945GCLF board. > > > > No, this isn't a good approach. A better fix would be to change the > > byte mask in do_scsi_command()'s SC_READ_TOC case. In the fourth > > argument to check_command(), change (7<<6) to (0xf<<6). It's hard to > > know whether this will fix the incorrect block size, though. > > > The X31 BIOS issues the READ_TOC command several times, > if it failes, no further attempts are made to boot from cd. Reissuing the command several times doesn't help if each time the command contains invalid data. > > But that's just a workaround. The fact is, the BIOS is sending > > incorrect data. The same is true with the 12-byte READ(10) command, > > although here g_file_storage accepts the bad length with only a > > warning. > > > Of course, it is a workaround. > With my first patch, which should break everything which cares about > the actual sector size (since I'm using 2048 only in the READ(x) command > but not in the READ_CAPACITY) but there seems to be no BIOS > using the sector size from the READ_CAPACITY command. Linux does honor > it and does not work with my patched g_file_storage. Originally I wrote the cdrom additions using a 2048-byte block size. This turned out to be quite messy, and when I realized that the SCSI spec allows a CD drive to use 512-byte blocks I gladly removed all the support for larger sectors. > I cleaned up the patch especially the sector size stuff and with that patch > I have installed ubuntu from a g_file_storage_gadget in cdrom mode successfully. Of course you didn't bother to change do_write() and a bunch of other places. Doing it properly means reintroducing all that mess, which I'm not anxious to do. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
