On 2021/07/23 1:14, Hannes Reinecke wrote:

On 7/21/21 12:42 PM, Damien Le Moal wrote:

quoted

Add the sd_read_cpr() function to the sd scsi disk driver to discover
if a device has multiple concurrent positioning ranges (i.e. multiple
actuators on an HDD). This new function is called from
sd_revalidate_disk() and uses the block layer functions
blk_alloc_cranges() and blk_queue_set_cranges() to set a device
cranges according to the information retrieved from log page B9h,
if the device supports it.

The format of the Concurrent Positioning Ranges VPD page B9h is defined
in section 6.6.6 of SBC-5.

Signed-off-by: Damien Le Moal <redacted>
---
  drivers/scsi/sd.c | 80 +++++++++++++++++++++++++++++++++++++++++++++++
  drivers/scsi/sd.h |  1 +
  2 files changed, 81 insertions(+)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index b8d55af763f9..b1e767a01b9f 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c

@@ -3125,6 +3125,85 @@ static void sd_read_security(struct scsi_disk *sdkp, unsigned char *buffer)
  		sdkp->security = 1;
  }
  
+static inline sector_t sd64_to_sectors(struct scsi_disk *sdkp, u8 *buf)
+{
+	return logical_to_sectors(sdkp->device, get_unaligned_be64(buf));
+}
+
+/**
+ * sd_read_cpr - Query concurrent positioning ranges
+ * @sdkp:	disk to query
+ */
+static void sd_read_cpr(struct scsi_disk *sdkp)
+{
+	unsigned char *buffer, *desc;
+	struct blk_cranges *cr = NULL;
+	unsigned int nr_cpr = 0;
+	int i, vpd_len, buf_len = SD_BUF_SIZE;
+
+	/*
+	 * We need to have the capacity set first for the block layer to be
+	 * able to check the ranges.
+	 */
+	if (sdkp->first_scan)
+		return;
+
+	if (!sdkp->capacity)
+		goto out;
+
+	/*
+	 * Concurrent Positioning Ranges VPD: there can be at most 256 ranges,
+	 * leading to a maximum page size of 64 + 256*32 bytes.
+	 */
+	buf_len = 64 + 256*32;
+	buffer = kmalloc(buf_len, GFP_KERNEL);
+	if (!buffer || scsi_get_vpd_page(sdkp->device, 0xb9, buffer, buf_len))
+		goto out;
+
+	/* We must have at least a 64B header and one 32B range descriptor */
+	vpd_len = get_unaligned_be16(&buffer[2]) + 3;
+	if (vpd_len > buf_len || vpd_len < 64 + 32 || (vpd_len & 31)) {
+		sd_printk(KERN_ERR, sdkp,
+			  "Invalid Concurrent Positioning Ranges VPD page\n");
+		goto out;
+	}
+
+	nr_cpr = (vpd_len - 64) / 32;
+	if (nr_cpr == 1) {
+		nr_cpr = 0;
+		goto out;
+	}
+
+	cr = blk_alloc_cranges(sdkp->disk, nr_cpr);
+	if (!cr) {
+		nr_cpr = 0;
+		goto out;
+	}
+
+	desc = &buffer[64];
+	for (i = 0; i < nr_cpr; i++, desc += 32) {
+		if (desc[0] != i) {
+			sd_printk(KERN_ERR, sdkp,
+				"Invalid Concurrent Positioning Range number\n");
+			nr_cpr = 0;
+			break;
+		}
+
+		cr->ranges[i].sector = sd64_to_sectors(sdkp, desc + 8);
+		cr->ranges[i].nr_sectors = sd64_to_sectors(sdkp, desc + 16);
+	}
+
+out:
+	blk_queue_set_cranges(sdkp->disk, cr);

See? We are _are_ creating a new set of ranges.
So why bother updating the old ones?

See my reply to my comments on patch 1. We do not update the old ones. The cases
are:
1) This is the first call, q->cranges is NULL: cr will become q->cranges.
2) q->cranges is already set and cr has the same info as q->cranges (no change):
cr will be freed by blk_queue_set_cranges().
3) q->cranges is already set and cr is different from q-cranges: q->cranges will
be completely dropped and cr become the new q->cranges.

So we never directly update anything inside q->cranges. We just swap in a new
full structure in case of change.

quoted

+	if (nr_cpr && sdkp->nr_actuators != nr_cpr) {
+		sd_printk(KERN_NOTICE, sdkp,
+			  "%u concurrent positioning ranges\n", nr_cpr);
+		sdkp->nr_actuators = nr_cpr;
+	}
+
+	kfree(buffer);
+}
+
  /*
   * Determine the device's preferred I/O size for reads and writes
   * unless the reported value is unreasonably small, large, not a

@@ -3240,6 +3319,7 @@ static int sd_revalidate_disk(struct gendisk *disk)
  		sd_read_app_tag_own(sdkp, buffer);
  		sd_read_write_same(sdkp, buffer);
  		sd_read_security(sdkp, buffer);
+		sd_read_cpr(sdkp);
  	}
  
  	/*

diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h
index b59136c4125b..2e5932bde43d 100644
--- a/drivers/scsi/sd.h
+++ b/drivers/scsi/sd.h

@@ -106,6 +106,7 @@ struct scsi_disk {
  	u8		protection_type;/* Data Integrity Field */
  	u8		provisioning_mode;
  	u8		zeroing_mode;
+	u8		nr_actuators;		/* Number of actuators */
  	unsigned	ATO : 1;	/* state of disk ATO bit */
  	unsigned	cache_override : 1; /* temp override of WCE,RCD */
  	unsigned	WCE : 1;	/* state of disk WCE bit */

Otherwise:

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes

-- 
Damien Le Moal
Western Digital Research