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On Dec 15, 2003, at 7:21 AM, Eric Haszlakiewicz wrote:

> 	yes, I do have some changes to pass more information about a read
> down farther.  Specifically, I mark the range mapped to read from a 
> file
> as needing all of it if done from a read() call and use that to adjust
> the amount of readahead to do.  mmap'd access still uses the normal
> readahead algo.  My code also extends the interface with the actual 
> device
> so it can say how much it can read at once, which would eventually 
> allow
> reads of more than 64k to happen.  I haven't been able to test that 
> very
> well b/c IDE drives (or at least mine) can't actually do more than 64k
> transfers.

It would be really cool if you could resurrect this stuff.

As far as the "larger than 64K reads" thing goes, yah, it is kind of 
annoying about any drive that uses the ATA command set has this 64K 
limitation (I think it's hard-wired into the spec, right?)

...but I would still like to fix the problem so that we can e.g. issue 
large I/Os to logical disks (e.g. ccds) that allow us to issue 64K I/Os 
to the disks themselves.

         -- Jason R. Thorpe <thorpej@wasabisystems.com>


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