On 30 Aug 2014, at 6:39, Stefan Fritsch <s...@sfritsch.de> wrote: > On Fri, 29 Aug 2014, Mike Belopuhov wrote: > >> On 29 August 2014 11:26, Stefan Fritsch <s...@sfritsch.de> wrote: >>> On Fri, 29 Aug 2014, Miod Vallat wrote: >>>>> sc->sc_xfer_max is computed according to the host's capabilities. What I >>>>> want to simulate with this diff is a host adapter that can only cope with >>>>> transfers < 64k == MAXPHYS. >>>> >>>> Back to your original problem, you might want to print the sc_link >>>> struct as well the scsi_adapter struct it points to, when you detect a >>>> transfer larger than MAXPHYS. It has likely been overriden or reset to >>>> NULL by mistake at some point. >>> >>> OK, I will try that. Will take a bit until I have time, though. > > That's not the problem. I have added an additional > > KASSERT(xs->sc_link->adapter->scsi_minphys == vioblk_minphys) > > before the other KASSERT and it did not trigger. > >>> But I have also read the code and I could not find a place in the path >>> from bread() to the scsi adapter cmd function where the minphys function >>> is called. >>> >> >> correct me if i'm wrong, but what happens is that bread being a block >> read reads up to MAXBSIZE which is conveniently set to 64k and you can't >> create a filesystem with a larger block size. >> >> physio (raw device io) however doesn't go through bread and need to know >> how split the provided buffer in separate transactions hence minphys. > > Yes, that seems to be what happens. But if every adapter needs to support > transfers of MAXBSIZE == MAXPHYS anyway, there would be no need for the > adapter to be able to override the default minphys function with its own. > And adapters that only support smaller transfers would need to have logic > in their driver to be able to split the transfer into smaller chunks. > > I think it makes more sense to have that logic in one place to be used by > all drivers.
this has blown my mind. how do the stupid ata cf card things that only support single sector IO work? dlg
