On Fri, 2013-03-15 at 10:46 +0100, Hannes Reinecke wrote:
> SAM advertises the use of a Well-known LUN (W_LUN) for scanning.
> As this avoids exposing LUN 0 (which might be a valid LUN) for
> all initiators it is the preferred method for LUN scanning on
> some arrays.
> So we should be using W_LUN for scanning, too. If the W_LUN is
> not supported we'll fall back to use LUN 0.
> For broken W_LUN implementations a new blacklist flag
> 'BLIST_NO_WLUN' is added.
Well, we could do this, but I don't really see the point. By the time
we get into the report lun code, we've already probed LUN 0, so it's as
good as any for a REPORT LUN scan.
What worries me slightly about the W-LUN is that for the first time
we'll be assuming a device supports a particular address method
(Extended Logical Unit addressing) rather than treating LUNs as opaque
handles we keep and pass back to the target. I appreciate you now have
a blacklist for failures, but if we didn't use W-LUNs we wouldn't need
that blacklist.
So could you answer two questions clearly:
1. What does this buy us over the current LUN0 method? I don't see
LUN0 might be a valid LUN being a convincing reason.
2. What devices have you actually tested this on?
James
> Signed-off-by: Hannes Reinecke <hare@xxxxxxx>
>
> diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
> index 3e58b22..f4ccdea 100644
> --- a/drivers/scsi/scsi_scan.c
> +++ b/drivers/scsi/scsi_scan.c
> @@ -1312,6 +1312,7 @@ static int scsi_report_lun_scan(struct scsi_target *starget, int bflags,
> unsigned int num_luns;
> unsigned int retries;
> int result;
> + int w_lun = SCSI_W_LUN_REPORT_LUNS;
> struct scsi_lun *lunp, *lun_data;
> u8 *data;
> struct scsi_sense_hdr sshdr;
> @@ -1337,11 +1338,20 @@ static int scsi_report_lun_scan(struct scsi_target *starget, int bflags,
> return 0;
> if (starget->no_report_luns)
> return 1;
> + if (bflags & BLIST_NO_WLUN)
> + w_lun = 0;
>
> +retry_report_lun_scan:
> if (!(sdev = scsi_device_lookup_by_target(starget, 0))) {
> - sdev = scsi_alloc_sdev(starget, 0, NULL);
> - if (!sdev)
> - return 0;
> + sdev = scsi_alloc_sdev(starget, w_lun, NULL);
> + if (!sdev) {
> + if (w_lun != 0) {
> + w_lun = 0;
> + sdev = scsi_alloc_sdev(starget, w_lun, NULL);
> + }
> + if (!sdev)
> + return 0;
> + }
> if (scsi_device_get(sdev)) {
> __scsi_remove_device(sdev);
> return 0;
> @@ -1418,6 +1428,18 @@ static int scsi_report_lun_scan(struct scsi_target *starget, int bflags,
> }
>
> if (result) {
> + if (w_lun != 0 && scsi_device_created(sdev)) {
> + /*
> + * W_LUN probably not supported, try with LUN 0
> + */
> + SCSI_LOG_SCAN_BUS(3, printk (KERN_INFO "scsi scan:"
> + "W_LUN not supported, try LUN 0\n"));
> + kfree(lun_data);
> + scsi_device_put(sdev);
> + __scsi_remove_device(sdev);
> + w_lun = 0;
> + goto retry_report_lun_scan;
> + }
> /*
> * The device probably does not support a REPORT LUN command
> */
> diff --git a/include/scsi/scsi_devinfo.h b/include/scsi/scsi_devinfo.h
> index cc1f3e7..ffb42b1 100644
> --- a/include/scsi/scsi_devinfo.h
> +++ b/include/scsi/scsi_devinfo.h
> @@ -31,4 +31,5 @@
> #define BLIST_MAX_512 0x800000 /* maximum 512 sector cdb length */
> #define BLIST_ATTACH_PQ3 0x1000000 /* Scan: Attach to PQ3 devices */
> #define BLIST_NO_DIF 0x2000000 /* Disable T10 PI (DIF) */
> +#define BLIST_NO_WLUN 0x4000000 /* Disable W_LUN scanning */
> #endif
> --
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