Re: [Iscsitarget-devel] [patch] user definable sector size

[Ross S. W. W. <RW...@me...>]

On Feb 26, 2010, at 6:18 PM, "Lars Ellenberg" <la...@li...> wrote:

> On Fri, Feb 26, 2010 at 05:01:46PM -0500, Ross S. W. Walker wrote:
> > > but, afaik,
> > > if you have a queue->limit.logical_block_size = 4096,
> > > it is illegal to submit a bio less than that, or unaligned.
> > > It just won't work.
> >
> > The current Linux block layer only accepts sector sizes of
> > 512 bytes.
> >
> > > Or I really need some sleep :)
>
> I seriously do _now_, but anyways...
>
> > Ok doing a simple grep for blk_shift:
> >
> > [root@storage2 kernel]# grep -n blk_shift *
> > iscsi.c:755:    *off <<= lu->blk_shift;
> > iscsi.c:756:    *len <<= lu->blk_shift;
>
> Yeah. But that is absolutely not what I meant.
>
> Ok, to make myself clear, attached is a very simple kernel module
> and Makefile.
> compile: make -C /usr/src/linux-headers-2.6.31-19-generic/ M=$PWD  
> modules
>
> It intentionally fails to load,
> but in the module init prepares one bio depending on module parameers,
> and does a submit_bio, and printk's some messages.
>
> To actually get the results needed to understand my point,
> you need a device with logical_block_size != 512.
>
> Even though these are shipping today
> already, they are still sufficiently rare that I did not see one
> in real life yet.
>
> But now we patched iet to provide that,
> that should be easy enough.
> At least that is my testing target now:
>
>         blockdev --getss /dev/sdb
>         2048
>
> Test run on
> Linux soda 2.6.31-19-generic #56-Ubuntu SMP Thu Jan 28 01:26:53 UTC  
> 2010 i686 GNU/Linux
>
>
> results in dmesg is interleaved,
> as I said, "Invalid parameters" is intentional.
> Have a look at when the "error: -5" occur.
>
> Hope you understand me this time,
> or point me were I'm still not getting it.
>
Can you post the code for the test module?

What you are basically saying is that the Linux block layer doesn't  
support devices whose sector size != 512.

I think we might need an outside opinion on this. Maybe Jens would  
reply to a query on this?

If that is the case then maybe blockio can't use a definable sector  
size?

-Ross


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