Messages in this thread | | | From | "Rob Turk" <> | Subject | Re: [PATCH] MODE SENSE in sd.c; sddr09.c | Date | Mon, 2 Sep 2002 13:00:39 +0200 |
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<Andries.Brouwer@cwi.nl> wrote in message news:cistron.UTC200209020041.g820fGS22828.aeb@smtp.cwi.nl... > In sd.c we call MODE SENSE (6) in order to find out whether the > device is write protected. The info we need is in byte 2, the > header of the MODE SENSE answer, but in the request we have to > specify (i) what page(s) we want, and (ii) how many bytes we want. > > Long ago we asked for 12 bytes from page 1 (Daniel Roche, 1.3.35). > Matthew Dharm made this 8 bytes from page 3F (all pages), patch-2.4.0-test8. > In patch-2.4.10 the 8 was increased to 255. > > I found on the one hand devices that only react to page 0 > (the vendor page), and return an error for page 3F. > And on the other hand devices that are unable to handle requests > for more bytes than they actually have. > > So, it seems that the cautious way to ask for MODE SENSE data is > to first ask for the header only, see how much is available, > and then ask for everything. > > The patch below first separates out the MODE SENSE call, > and then tries it three times: on all pages (3F), only the first > four bytes; on the vendor page (0), only the first four bytes; > on all pages (3F), 255 bytes. >
Andries,
Would it be possible to move away from using 'standard' 255 bytes? Many SCSI device don't like requests for odd byte counts on 16-bit SCSI busses, and IDE isn't too crazy about it either. How about asking for 254 instead??
Rob
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