Re: Change in reported values of some block integrity sysfs attributes

[Anuj Gupta <anuj20.g@samsung.com>]

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On Fri, Feb 21, 2025 at 04:07:55PM +0530, Anuj gupta wrote:
> > I don't see any change in what's reported with block/for-next in a
> > regular SCSI HBA/disk setup. Will have to look at whether there is a
> > stacking issue wrt. multipathing.
> 
> Hi Martin, Christoph,
> 
> It seems this change in behaviour is not limited to SCSI only. As Nikhil
> mentioned an earlier commit
> [9f4aa46f2a74 ("block: invert the BLK_INTEGRITY_{GENERATE,VERIFY} flags")]
> causes this change in behaviour. On my setup with a NVMe drive not formatted
> with PI, I see that:
> 
> Without this commit:
> Value reported by read_verify and write_generate sysfs entries is 0.
> 
> With this commit:
> Value reported by read_verify and write_generate sysfs entries is 1.
> 
> Diving a bit deeper, both these flags got inverted due to this commit.
> But during init (in nvme_init_integrity) these values get initialized to 0,
> inturn setting the sysfs entries to 1. In order to fix this, the driver has to
> initialize both these flags to 1 in nvme_init_integrity if PI is not supported.
> That way, the value in sysfs for these entries would become 0 again. Tried this
> approach in my setup, and I am able to see the right values now. Then something
> like this would also need to be done for SCSI too.
> 

I tried to make it work for SCSI too. However my testing is limited as I
don't have a SCSI device. With scsi_debug I see this currently:

# modprobe scsi_debug dev_size_mb=128 dix=0 dif=0
# cat /sys/block/sda/integrity/write_generate
1
# cat /sys/block/sda/integrity/read_verify
1
# cat /sys/class/scsi_host/host0/prot_capabilities
0

To fix this, I added this. Nikhil can you try below patch? Martin, can
you please take a look as well.

After this patch, with the same scsi_debug device, I see sysfs entries
populated as 0.

diff --git a/drivers/scsi/sd_dif.c b/drivers/scsi/sd_dif.c
index ae6ce6f5d622..be2cd06f500b 100644
--- a/drivers/scsi/sd_dif.c
+++ b/drivers/scsi/sd_dif.c
@@ -40,8 +40,10 @@ void sd_dif_config_host(struct scsi_disk *sdkp, struct queue_limits *lim)
 		dif = 0; dix = 1;
 	}
 
-	if (!dix)
+	if (!dix) {
+		bi->flags |= BLK_INTEGRITY_NOGENERATE | BLK_INTEGRITY_NOVERIFY;
 		return;
+	}
 
 	/* Enable DMA of protection information */
 	if (scsi_host_get_guard(sdkp->device->host) & SHOST_DIX_GUARD_IP)

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