Quoting Helen Koike (2019-06-04 10:38:59) > On 6/3/19 8:02 PM, Stephen Boyd wrote: > > > > I'm trying to boot a mainline linux kernel on a chromeos device with dm > > verity and a USB stick but it's not working for me even with this patch. > > I've had to hack around two problems: > > > > 1) rootwait isn't considered > > > > 2) verity doesn't seem to accept UUID for <hash_dev> or <dev> > > > > For the first problem, it happens every boot for me because I'm trying > > to boot off of a USB stick and it's behind a hub that takes a few > > seconds to enumerate. If I hack up the code to call dm_init_init() after > > the 'rootdelay' cmdline parameter is used then I can make this work. It > > would be much nicer if the whole mechanism didn't use a late initcall > > though. If it used a hook from prepare_namespace() and then looped > > waiting for devices to create when rootwait was specified it would work. > > The patch was implemented with late initcall partially to be contained > in drivers/md/*, but to support rootwait, adding a hook from > prepare_namespace seems the way to go indeed. Alright, great. > > > > > The second problem is that in chromeos we have the bootloader fill out > > the UUID of the kernel partition (%U) and then we have another parameter > > that indicates the offset from that kernel partition to add to the > > kernel partition (typically 1, i.e. PARTNROFF=1) to find the root > > filesystem partition. The way verity seems to work here is that we need > > to specify a path like /dev/sda3 or the major:minor number of the device > > on the commandline to make this work. It would be better if we could add > > in support for the PARTNROFF style that name_to_dev_t() handles so we > > can specify the root partition like we're currently doing. I suspect we > > should be able to add support for this into the device mapper layer so > > that we can specify devices this way. > > hmm, I didn't test this yet but at least from what I can see in the > code, verity_ctr() calls dm_get_device() that ends up calling > name_to_dev_t() which should take care of PARTNROFF, this requires a bit > more investigation. > Ok, thanks for pointing that out. Sorry I totally missed this codepath and I should have investigated more. It works for me with the PARTNROFF syntax that we've been using, so the problem is the rootwait stuff.
