Re: PATCH: usb-storage-set-last-sector-bug-flag.patch

[Stefan Richter <stefanr@xxxxxxxxxxxxxxxxx>]

Greg KH wrote:
> I just am worried that we are
> now suddenly keeping access from the last sector for devices that
> currently did work just fine.

This new workaround doesn't prevent access to the last sector.  It only
breaks up a multi-sector access which would also reach the last sector
into several (two? I'm too lazy to look back in the mail thread)
accesses, in order to access the last sector in a dedicated
single-sector access.

So that's very differently to the fix-capacity workaround.  The
fix-capacity workaround manipulates the READ CAPACITY parameter data.
Therefore the fix-capacity workaround is unsafe for non-buggy devices.

The last-sector-(access-)bug workaround _only_ modifies the command
stream which is sent to the device.  A dangerous command is replaced by
equivalent safe commands.  These commands are luckily safe for _all_
devices, buggy and non-buggy ones.  The only cost of this workaround is
(1.) the code, (2.) the runtime/ bandwidth/ latency overhead for
accesses which reach the last sector.

Somebody correct me if I got something wrong.
-- 
Stefan Richter
-=====-==--- ---= ==---
http://arcgraph.de/sr/

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