Re: [PATCH] SCSI: erase invalid data returned by device

[Elias Oltmanns <eo@nebensachen.de>]

James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> On Wed, 2008-07-16 at 15:41 +0200, Elias Oltmanns wrote:
>> Alan Stern <stern@rowland.harvard.edu> wrote:
[...]
>> > +		memset(buffer + (bufflen - req->data_len), 0, req->data_len);
>> 
>> Sorry, I don't understand that line at all. Surely, we want to zero out
>> either the excess data, i.e. buffer -> buffer + req->data_len, or the
>> residue, i.e. buffer + req->data_len -> buffer + bufflen. Your patch
>> implies that there are bufflen - req->data_len bytes of valid data at
>> the beginning of buffer. If this is intentional, please bear with me and
>> explain. Otherwise, what about the following patch to 2.6.26? On the
>> other hand, the same could probably be achieved by setting req->data_len
>> to 0. Oh dear, it would appear that I'm completely lost here.
>
> I think all you don't understand is simply that for a REQ_BLOCK_PC, the
> residue (that's the amount of untransferred, or at least bogus, data) is
> returned in req->data_len.  Thus, after such a request completes, you
> have bufflen-req->data_len good bytes.

Oh, I see. The name fooled me there, I suppose. So, the meaning of
req->data_len is inverted, as it were, when the LLDD performs the data
transfer, right?

Thanks for explaining,

Elias