Re: another unusual flag for a really limited device

On Wed, Nov 14, 2007 at 12:28:03PM -0500, Alan Stern wrote:
> On Tue, 13 Nov 2007, Matthew Dharm wrote:
> 
> > On Tue, Nov 13, 2007 at 07:35:45PM -0600, Doug Maxey wrote:
> > > Have run across a virtual USB host that needs (yes, I know, a strong
> > > word :) to limit the maximum number of sectors transferred in a single
> > > request to 32.  In theory, the device should be fine with 32k, but
> > > when it loses, it never seems to recover without a full reset.
> > > 
> > > Did some searching in the archives, but saw nothing.
> > > 
> > > What about something along the lines of adding UL_FL_MAX_SECTORS_32 to
> > > follow the pattern used with MAX_SECTORS_64, thusly?
> > > 
> > > Based on linus 2.6.24-rc2.
> > 
> > I can't say I'm really happy about another flag, but I can't exactly object
> > too strongly.  This is probably the best fix we're going to find.
> > 
> > Tho, I'm seriously tempted to make the choice MAX_SECTORS_64 and
> > MAX_SECTORS_1 -- if a device can't handle 64 sectors at a time, then let's
> > just limit it to 1 and call it a day.   Otherwise we're going to wind up
> > with MAX_SECTORS_32, _16, _8, _4, and _2 someday.
> 
> 1 won't work; max_sectors has to be at least the size of a memory
> page.  This is enforced by the block layer's request_queue routines.
> But we certainly could have a MAX_SECTORS_MIN flag.

So, for most systems, the limit is 8?

Whatever our functional lower limit is, I think agree that a _MIN flag
would make sense.

I'm somewhat tempted to actually just convert the _64 flag to a _MIN flag,
and make the issue of finding an "optimal" value a userspace problem.  I
think you can get to this parameter via sysfs, right?

Matt

-- 
Matthew Dharm                              Home: [email protected] 
Maintainer, Linux USB Mass Storage Driver

But where are the THEMES?!  How do you expect me to use an OS without 
themes?!
					-- Stef
User Friendly, 10/9/1998

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