Re: scsi_alloc_target: parent of the target (need not be a scsi host)

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Sun, 2020-05-10 at 14:32 -0400, Douglas Gilbert wrote:
> This gem is in scsi_scan.c in the documentation of that function's
> first argument. "need not be a scsi host" should read "it damn well
> better be a scsi host" otherwise that function will crash and burn!

It shouldn't: several transport classes, like SAS and FC have
intermediate devices between the host and the target and they all work
just fine using the non-host parent.  Since you don't give the error
this is just guesswork, but the host has to be somewhere in the parent
chain otherwise dev_to_shost(parent) will return NULL ... is that your
problem?

> I'm trying to work out why the function: starget_for_each_device() in
> scsi.c does _not_ use that collection right in front of it (i.e.
> scsi_target::devices). Instead, it step up to the host level, and
> iterates over all devices (LUs) on that host and only calls the given
> function for those devices that match the channel and target numbers.
> That is bizarrely wasteful if scsi_target::devices could be iterated
> over instead.
> 
> Anyone know why this is?

Best guess would be it wasn't converted over when the target list was
introduced.

James