Re: another unusual flag for a really limited device

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.

Alan Stern


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