Re: [PATCHv2] scsi: disable automatic target scan

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

On 03/15/2016 08:19 AM, Hannes Reinecke wrote:
> On larger installations it is useful to disable automatic LUN
> scanning, and only add the required LUNs via udev rules.
> This can speed up bootup dramatically.
>
> This patch introduces a new scan module parameter value 'manual',
> which works like 'none', but can be overriden by setting the 'rescan'
> value from scsi_scan_target to 'SCSI_SCAN_MANUAL'.
> And it updates all relevant callers to set the 'rescan' value
> to 'SCSI_SCAN_MANUAL' if invoked via the 'scan' option in sysfs.
>
> Signed-off-by: Hannes Reinecke <hare@suse.de>
> ---

> +MODULE_PARM_DESC(scan, "sync, async, manual, or none. "
> +		 "Setting to 'manual' disables automatic scanning, but allows "
> +		 "for manual device scan via the 'scan' sysfs attribute.");

nice solution

> + * @rescan:	passed to LUN scanning routines; SCSI_SCAN_NONE for no rescan,
> + *              SCSI_SCAN_RESCAN to rescan existing LUNs, and SCSI_SCAN_MANUAL
> + *              to force scanning even if 'scan=manual' is set.

> @@ -1621,6 +1627,10 @@ void scsi_scan_target(struct device *parent, unsigned int channel,
>   	if (strncmp(scsi_scan_type, "none", 4) == 0)
>   		return;
>
> +	if (rescan < SCSI_SCAN_MANUAL &&
> +	    strncmp(scsi_scan_type, "manual", 6) == 0)
> +		return;
> +

I see that the ordering of identifiers in enum scsi_scan_mode allows a 
nice inequation here.

However, it also seems that we need to touch all callers (which intend 
an unconditional manual scan) of scsi_scan_target() that used to call it 
with rescan==1 which would now be rescan==SCSI_SCAN_MANUAL==2 ?

Or could we define the ordering of identifiers in enum scsi_scan_mode 
such that SCSI_SCAN_MANUAL happens to remain 1 so we don't have to touch 
many callers (probably there would still remain some callers we would 
have to touch because 1 does not mean MANUAL but RESCAN there)?

In particular, the following might be necessary in order not to break 
zfcp manual LUN addition (as long as zfcp still has its own unit_add 
sysfs interface; completely replacing it with the solution here is not 
easy because it breaks the zfcp sysfs user interface):

> void zfcp_unit_scsi_scan(struct zfcp_unit *unit)
> {
> 	struct fc_rport *rport = unit->port->rport;
> 	u64 lun;
>
> 	lun = scsilun_to_int((struct scsi_lun *) &unit->fcp_lun);
>
> 	if (rport && rport->port_state == FC_PORTSTATE_ONLINE)
>- 		scsi_scan_target(&rport->dev, 0, rport->scsi_target_id, lun, 1);
>+ 		scsi_scan_target(&rport->dev, 0, rport->scsi_target_id, lun,
>+ 				 SCSI_SCAN_MANUAL);
> }

Not sure about: mpt_work_wrapper(), snic_scsi_scan_tgt().

> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -143,7 +143,8 @@ static int scsi_scan(struct Scsi_Host *shost, const char *str)

> +		res = scsi_scan_host_selected(shost, channel, id, lun,
> +					      SCSI_SCAN_MANUAL);

> +++ b/drivers/scsi/scsi_transport_fc.c
> @@ -2110,7 +2110,8 @@ fc_user_scan_tgt(struct Scsi_Host *shost, uint channel, uint id, u64 lun)

> +			scsi_scan_target(&rport->dev, channel, id, lun,
> +					 SCSI_SCAN_MANUAL);

> +++ b/drivers/scsi/scsi_transport_iscsi.c
> @@ -1819,7 +1819,7 @@ static int iscsi_user_scan_session(struct device *dev, void *data)

>   			scsi_scan_target(&session->dev, 0, id,
> +					 scan_data->lun, SCSI_SCAN_MANUAL);

> +++ b/drivers/scsi/scsi_transport_sas.c
> @@ -1739,8 +1739,8 @@ static int sas_user_scan(struct Scsi_Host *shost, uint channel,

> +			scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id,
> +					 lun, SCSI_SCAN_MANUAL);

> +++ b/include/scsi/scsi_device.h

> +enum scsi_scan_mode {
> +	SCSI_SCAN_NONE = 0,
> +	SCSI_SCAN_RESCAN,
> +	SCSI_SCAN_MANUAL,
> +};

-- 
Mit freundlichen Grüßen / Kind regards
Steffen Maier

Linux on z Systems Development

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