Re: [PATCH 0/2] scsi_transport_fc: LUN masking

[Steffen Maier <maier@linux.vnet.ibm.com>]

Hi Hannes,

On 11/11/2015 11:34 AM, Hannes Reinecke wrote:
> having been subjected to the pain of trying to bootstrap a really
> large machine with systemd I decided to implement LUN masking in

This is very interesting.

I also thought about initiator-based LUN masking a while ago.
While scsi_transport_fc would be sufficient to allow zfcp to get rid of 
its own implementation, I wonder why we wouldn't do it in the midlayer's 
scsi_scan.c. This would provide initiator-based LUN masking for any and 
all transports and LLDDs?

(I also thought about initiator-based zoning, and that would indeed be 
something for scsi_transport_fc because it is inherently transport 
specific.)

> scsi_transport_fc.
> The principle is simple: disallow the automated LUN scanning when
> discovering a rport, and create udev rules which selectively
> enable individual LUNs by echoing the relevant values in the 'scan'
> attribute of the SCSI host.

I imagined exactly the same existing user space interface.

Now we "only" need some user-friendly user space tooling, which provides 
transport specific user arguments automatically translated into the 
midlayer naming scheme, such as converting FC SAN addressing (HBA device 
bus-ID,WWPN,FCPLUN) into scsi_device names (Scsi_Host,0,scsi_id,scsi_lun),
and some persistency mechanism (such as managing udev rules).

> With that I'm able to boot an arbitrary large machine without
> running into any udev or systemd imposed timeout.
> To _disable_ LUN masking and restoring the original behaviour
> I've noticed that the 'scan' sysfs attribute is actually synchronous,
> ie the calling process will be blocked until the entire LUN scan
> is completed.
> So I've added another module parameter 'async_user_scan' to
> move the scanning onto the existing scan workqueue, and unblock
> the calling process.

Just curious: Which means would a user of async_user_scan have to sync 
against the completion?
Or is this only meant for user space--I currently cannot imagine--which 
does not care about the appearance of what was (newly) discovered?

>
> As usual, comments and reviews are welcome.
>
> Hannes Reinecke (2):
>    scsi_transport_fc: implement 'disable_target_scan' module parameter
>    scsi_transport_fc: Implement 'async_user_scan' module parameter
>
>   drivers/scsi/scsi_transport_fc.c | 47 +++++++++++++++++++++++++++++++++++++---
>   1 file changed, 44 insertions(+), 3 deletions(-)
>

-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

Linux on z Systems Development

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