linux-kernel - Re: get/put unaligned helpers

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Date:	Fri, 13 Feb 2009 14:07:02 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	Christoph Hellwig <hch@....de>
Cc:	linux-kernel@...r.kernel.org, Boaz Harrosh <bharrosh@...asas.com>,
	Matthew Wilcox <matthew@....cx>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: get/put unaligned helpers

On Wed, 2009-02-11 at 15:35 +0100, Christoph Hellwig wrote:
> I just loked into using the new get/put unaligned helpers.  I must
> say that I'm really unhappy about the lack of typing there.  We did
> put all the sparse infrastructure in place to make sure we do have
> strong typechecking for LE/Be types, but using these helpers defeats
> that.
> 
> Can you please make these properly typed?

Christoph, here's a quick summary of comments on the unaligned access bits
I've previously submitted, please let me know if you have any additional ones.

Proposed API:

u16 load_le16_noalign(const __le16 *p)
u32 load_le32_noalign(const __le32 *p)
u64 load_le64_noalign(const __le64 *p)
u16 load_be16_noalign(const __be16 *p)
u32 load_be32_noalign(const __be32 *p)
u64 load_be64_noalign(const __be64 *p)

void store_le16_noalign(__le16 *p, u16 val)
void store_le32_noalign(__le32 *p, u32 val)
void store_le64_noalign(__le64 *p, u64 val)
void store_be16_noalign(__be16 *p, u16 val)
void store_be32_noalign(__be32 *p, u32 val)
void store_be64_noalign(__be64 *p, u64 val)

I'd also like to offer aligned versions like load_le16() store_le16()
to make it symmetric.  Then for arches that have no alignment constraints
the unaligned helpers would degrade to the aligned helpers.  load_le16()
already exists as le16_to_cpup, but store_le16 would be a new API.

Now, from discussions with the SCSI-folks, they really aren't interested in a
typesafe interface as most of the time they are reading/writing into a u8 buffer
at some offset.  It seems a lot of the other places currently in-kernel also
do the same.  So I'm tempted to keep offering a version wrapped around the
typesafe versions that takes a u8 *.

As they were not interested in doing the following:

load_be16_noalign((__be16 *)&buf[offset]);

Perhaps a wrapper could be provided:

load_be16_offset(u8 *buf, int offset)

Thoughts?

Harvey

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