Re: [PATCH 0/2] convert libsas to the libata new eh

[James Bottomley <James.Bottomley@suse.de>]

On Tue, 2011-02-15 at 02:03 -0500, Jeff Garzik wrote:
> On 02/13/2011 02:18 PM, James Bottomley wrote:
> > On Sun, 2011-01-23 at 09:41 -0600, James Bottomley wrote:
> >> The bad news is that this is a pretty horrific conversion.  Because of
> >> the amount of control the new eh wants (and the slew of monolithic
> >> assumptions it makes), the entire error handler routine has to be sliced
> >> apart and sewn back together to make it callable as part of an existing
> >> error handler (rather than trying to do everything on its own).
> >>
> >> The even worse news is that unless you have an existing strategy
> >> handler, you can't make use of this.  That means that ipr is
> >> unconvertable in its current form.  Given the two really nasty options:
> >> give ipr its own error handler via its own transport class, or attach
> >> ipr to libsas and let it do the work, I'd choose the latter.
> >> Unfortunately, my power box with IPR has been non-functional for a year
> >> (and all pleas to IBM to fix it have so far gone unanswered), so I can't
> >> really do this myself.
> >>
> >> Once we carve up libata, it's still a rather complex call sequence for
> >> libsas because of libata's annoying insistance on calling the error
> >> handler at the drop of a hat.  The principle differentiator used is the
> >> fact that if a SCSI command no longer has an associated SAS task, (i.e.
> >> libsas thinks it's complete) it must be destined for libata.  This works
> >> correctly in all the ATAPI sense processing instances I've tested.
> >> Finally, we still have to call port recovery.  Currently, it's
> >> impossible to tell which port libata thinks is in error (libata knows
> >> because it has one host per port, but libsas doesn't), so the final
> >> solution is just to call port recovery for every SATA/STP attached port.
> >>
> >> I've tested all of this with mvsas over expander attached ATA devices
> >> using STP (aic94xx seems to have developed some handling fault for STP,
> >> which I'll look into next).
> >
> > Since there's been remarkably little discussion of the ata changes, I
> > think it's time to put this in linux-next to see what shakes out.
> 
> The fix series was quite straightforward, and the error handler 
> separation is almost mechanical.  All looks good and tests well here, so 
> I threw it into libata-dev.git#upstream (and thus linux-next).

Well, as you know, it's already in scsi-misc; as long as we don't get a
merge conflict in linux-next, I don't really care.

However, since it's a SCSI feature, which depends on patches in the scsi
tree both before and after, it doesn't make a whole lot of sense in the
ata tree.  It's just one actual patch that is libata impacting (the eh
split).  The other three correct the sas paths, which only have SCSI
users.

> Let me know if you want to peel off patch 2/2 here into a post-merge tree...

Well, you're missing the precursor patches to make it functional ...
what you have will hang fairly fast on an actual SAS device.  But, as
long as people with SAS only test scsi-misc or linux-next, hopefully it
won't matter.

James