[PATCH v2 2/4] scsi: core: Read the ALUA access state when a device is scanned

[Brian Bunker <brian@purestorage.com>]

sdev->access_state is only set by a device handler, and the ALUA
device handler reads it with an RTPG it queues when it attaches, which
normally completes after the device has been registered and matched to
a driver. The SCSI core therefore has no ALUA state for a device while
it decides whether to bind an upper-level driver to it.

For a device that reports TPGS support, send REPORT TARGET PORT GROUPS
from scsi_add_lun(), after the VPD pages have been read, and set
sdev->access_state from the descriptor of the target port group of
this path. UNIT ATTENTIONs, which a target typically reports first
after a login or an ALUA state change, are retried, and the command is
resent without the extended header if the target rejects it. If the
command fails, e.g. with LOGICAL UNIT NOT SUPPORTED because no LU is
mapped at the LUN, sdev->access_state is left as it is.

The command uses the same timeout as the INQUIRY of the scan. The ALUA
device handler keeps updating sdev->access_state afterwards as before.

Suggested-by: Hannes Reinecke <hare@kernel.org>
Co-developed-by: Krishna Kant <krishna.kant@purestorage.com>
Signed-off-by: Krishna Kant <krishna.kant@purestorage.com>
Signed-off-by: Brian Bunker <brian@purestorage.com>
---
 drivers/scsi/scsi_scan.c | 94 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 94 insertions(+)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 8aae12fd38f3..a21dee1d9e9e 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -861,6 +861,93 @@ static int scsi_probe_lun(struct scsi_device *sdev, unsigned char *inq_result,
 	return 0;
 }
 
+/**
+ * scsi_read_access_state - Read the ALUA state of a device
+ * @sdev: SCSI device that supports target port groups
+ *
+ * Send REPORT TARGET PORT GROUPS and set sdev->access_state to the
+ * asymmetric access state that the device reports for the target port
+ * group of this path, as identified in VPD page 0x83. If the command
+ * fails, e.g. with LOGICAL UNIT NOT SUPPORTED because no LU is mapped at
+ * this LUN for this I_T nexus, sdev->access_state is left unchanged. The
+ * ALUA device handler, if attached, keeps the state up to date later.
+ */
+static void scsi_read_access_state(struct scsi_device *sdev)
+{
+	/*
+	 * Each UNIT ATTENTION reports a different condition queued for this
+	 * I_T nexus, e.g. a power on or reset after login followed by ALUA
+	 * state and INQUIRY data changes, so retry until the target answers
+	 * the command itself.
+	 */
+	struct scsi_failure failure_defs[] = {
+		{
+			.sense_key = UNIT_ATTENTION,
+			.sense_code = SCMD_FAILURE_SENSE_CODE_ANY,
+			.allowed = 5,
+			.result = SAM_STAT_CHECK_CONDITION,
+		},
+		{}
+	};
+	struct scsi_failures failures = {
+		.failure_definitions = failure_defs,
+	};
+	struct scsi_sense_hdr sshdr;
+	const struct scsi_exec_args exec_args = {
+		.sshdr = &sshdr,
+		.failures = &failures,
+	};
+	/* scsi_report_tpgs() replaces the buffer if this is too small */
+	int bufflen = 128;
+	int group_id, len, k, off;
+	unsigned char *buff, *desc;
+	bool ext_hdr = true;
+	int ret;
+
+	group_id = scsi_vpd_tpg_id(sdev, NULL);
+	if (group_id < 0)
+		return;
+
+	buff = kzalloc(bufflen, GFP_KERNEL);
+	if (!buff)
+		return;
+
+ retry:
+	ret = scsi_report_tpgs(sdev, &buff, &bufflen, ext_hdr,
+			       HZ / 2 + HZ * scsi_inq_timeout, 3, &exec_args);
+	if (ret) {
+		/*
+		 * Some targets reject the extended header format with
+		 * ILLEGAL REQUEST (see alua_rtpg()), so retry without it,
+		 * unless the reason is that no LU is mapped at this LUN.
+		 */
+		if (ret > 0 && ext_hdr && scsi_sense_valid(&sshdr) &&
+		    sshdr.sense_key == ILLEGAL_REQUEST &&
+		    sshdr.sense_code != LU_NOT_SUPPORTED) {
+			ext_hdr = false;
+			goto retry;
+		}
+		goto out;
+	}
+
+	len = get_unaligned_be32(&buff[0]) + 4;
+	if ((buff[4] & RTPG_FMT_MASK) == RTPG_FMT_EXT_HDR)
+		k = 8;
+	else
+		k = 4;
+
+	for (desc = buff + k; k + 8 <= len; k += off, desc += off) {
+		off = 8 + (desc[7] * 4);
+		if (get_unaligned_be16(&desc[2]) == group_id) {
+			sdev->access_state = desc[0];
+			break;
+		}
+	}
+
+ out:
+	kfree(buff);
+}
+
 /**
  * scsi_add_lun - allocate and fully initialize a scsi_device
  * @sdev:	holds information to be stored in the new scsi_device
@@ -1126,6 +1213,13 @@ static int scsi_add_lun(struct scsi_device *sdev, unsigned char *inq_result,
 
 	scsi_cdl_check(sdev);
 
+	/*
+	 * Read the ALUA state before the device is registered, so that
+	 * scsi_bus_match() can use it. This needs VPD page 0x83.
+	 */
+	if (scsi_device_tpgs(sdev))
+		scsi_read_access_state(sdev);
+
 	sdev->max_queue_depth = sdev->queue_depth;
 	WARN_ON_ONCE(sdev->max_queue_depth > sdev->budget_map.depth);
 
-- 
2.56.0