USB usages?(Ben)

Bas Wijnen wijnen at debian.org
Fri Jun 10 17:43:28 EDT 2011


Op 10-06-11 19:28, Joshua Judson Rosen schreef:
> And this is exactly the behaviour of my Android tablet and my (now-dead)
> iPod: you can't use the device for something else while simultaneously
> using it in `mass storage device' mode.

I think this is a limitation of the protocol. The host is allowed to
cache things, which means that proper locking is impossible. And without
locking, both systems (the PC and the NanoNote) can't both know that the
data on disk is consistent with itself. However, the underlying protocol
is SCSI; I'm not sure if the device can force the host cache to be
turned off. If it can, it should be possible to have simultaneous write
access as well (assuming all hosts support that; I wouldn't be too sure).

However, in many cases read-only mass-storage is enough. If nobody
writes to the data, there is no problem in having simultaneous reads
from different systems. AFAIK the Linux mass-storage server doesn't
enforce not writing (although it does mention it in the docs), and it
also doesn't forbid reading. So you should be able to have a partition
or file mounted as read-only loopback on the NanoNote, while also
serving it as read-only to a USB host.

Thanks,
Bas




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