Re: [PATCH] SCSI/libsrp: fix bug in ADDITIONAL CDB LENGTH interpretation

[Bart Van Assche <bart.vanassche@gmail.com>]

On Wed, Dec 9, 2009 at 8:04 PM, Matthew Wilcox <matthew@wil.cx> wrote:
>
> On Wed, Dec 09, 2009 at 07:52:19PM +0100, Bart Van Assche wrote:
> > Fix a bug in the interpretation of the ADDITIONAL CDB LENGTH (add_cdb_len)
> > field of SRP_CMD requests. According to the SRP specification, the layout
> > of this single-byte field is as follows:
> > * Bits 0 and 1 are reserved.
> > * Bits 2 to 7 represent the ADDITIONAL CDB LENGTH field, symbolically
> >   represented as n.
> > * Still according to the SRP specification, the ADDITIONAL CDB section
> >   takes 4*n bytes.
>
> Your interpretation of the SRP spec does seem to be correct, and I can
> totally see how the original author of this code got it wrong.
>
> > -     offset = cmd->add_cdb_len * 4;
> > +     offset = (cmd->add_cdb_len >> 2) * 4;
>
> Would this not be better written as:
>
>        offset = cmd->add_cdb_len & ~3;

I chose the former because of better readability for someone familiar
with the specs. But I do not have a strong opinion about this -- more
opinions are welcome.

Bart.
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