Subject: Re: The meaning of scsipi_minphys
To: Lennart Augustsson <>
From: Manuel Bouyer <>
List: tech-kern
Date: 03/27/2000 23:21:28
On Mon, Mar 27, 2000 at 01:01:39PM +0200, Lennart Augustsson wrote:
> What is the purpose of the scsipi_minphys() function pointer in the
> scsipi_adapter struct?
> I thought it could be used to give an upper bound on the amount of
> data that is given to the scsipi_cmd() function.
> This interpretation is obviously wrong, because I use the minphys
> function to limit the bp->b_bcount to 16K, but scsipi_cmd() is happily
> given larger chunks to transfer despite this.

yes, because for a block I/O scsipi_minphys() is not used.

> If this is not the way to limit the size, how can I limit it?  If I can't limit
> it, what is the minimum that a driver has to be able to handle?

Currently MAXPHYS.

Some time ago I haked something so that physical drivers could pass this info
to upper layer to use instead of MAXPHYS (I think this info was stored in
'struct disk'), and posted the patch in tech-kern.
I can't reach mail-index rigth now but I think you should be able tp find
it here (look for MAXPHYS). This was not especially hard to implement,
only a few hours work.

Manuel Bouyer, LIP6, Universite Paris VI.