linux-kernel - Re: [RFC-v4 07/12] iscsi-target: Add CHAP Authentication support using libcrypto

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Date:	Mon, 21 Mar 2011 18:50:51 -0700
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Christoph Hellwig <hch@....de>, Hannes Reinecke <hare@...e.de>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Boaz Harrosh <bharrosh@...asas.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Douglas Gilbert <dgilbert@...erlog.com>,
	Jesper Juhl <jj@...osbits.net>
Subject: Re: [RFC-v4 07/12] iscsi-target: Add CHAP Authentication support
	using libcrypto

On Mon, 2011-03-21 at 20:05 -0500, Mike Christie wrote:
> On 03/20/2011 04:31 AM, Nicholas A. Bellinger wrote:
> > +static struct iscsi_chap *chap_server_open(
> > +	struct iscsi_conn *conn,
> > +	struct iscsi_node_auth *auth,
> > +	const char *A_str,
> > +	char *AIC_str,
> > +	unsigned int *AIC_len)
> 
> Lot of mixed cases like this and below in the patch.
>
> > +static int chap_server_compute_md5(
> > +	struct iscsi_conn *conn,
> > +	struct iscsi_node_auth *auth,
> > +	char *NR_in_ptr,
> > +	char *NR_out_ptr,
> > +	unsigned int *NR_out_len)
> 
> 

<nod>, fixing this up in lio-4.1 now..

> 
> > +	return 2;
> > +}
> > diff --git a/drivers/target/iscsi/iscsi_target_auth.h b/drivers/target/iscsi/iscsi_target_auth.h
> > new file mode 100644
> > index 0000000..17b042d
> > --- /dev/null
> > +++ b/drivers/target/iscsi/iscsi_target_auth.h
> 
> 
> 
> > +
> > +struct iscsi_chap {
> > +	unsigned char	digest_type;
> > +	unsigned char	id;
> > +	unsigned char	challenge[CHAP_CHALLENGE_LENGTH];
> > +	unsigned int	challenge_len;
> > +	unsigned int	authenticate_target;
> > +	unsigned int	chap_state;
> > +} ____cacheline_aligned;
> > +
> 
> Why are almost all structs in the patches ____cacheline_aligned? Is it 
> something we are just doing now, or does this affect performance somehow 
> even though the struct is not used in a perf path?

For this particular case I wanted to make sure it was at least 32-bit
word aligned for ARM to avoid the unaligned penalites for the single
byte unsigned chars.

There is also a handful of single byte unsigned chars, u8, and u16
structure membmer usage in iscsi_target_core.h that is using
____cacheline_aligned using in the non performance critical path.
I would be happy to do a audit on these and convert to using the packed
attributed..

Just to double check, what is mainline convention for handling
structures like this for 32-bit word aligned ISAs..?

Thanks for your review Mike!

--nab


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