target: Untangle front-end and back-end meanings of max_sectors attribute

se_dev_attrib.max_sectors currently has two independent meanings:

 - It is reported in the block limits VPD page as the maximum transfer
   length, ie the largest IO that the front-end (fabric) can handle.
   Also the target core doesn't enforce this maximum transfer length.

 - It is used to hold the size of the largest IO that the back-end can
   handle, so we know when to split SCSI commands into multiple tasks.

Fix this by adding a new se_dev_attrib.fabric_max_sectors to hold the
maximum transfer length, and checking incoming IOs against that limit.
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_cdb.c

@@ -456,7 +456,7 @@ target_emulate_evpd_b0(struct se_cmd *cmd, unsigned char *buf)
 	/*
 	 * Set MAXIMUM TRANSFER LENGTH
 	 */
-	put_unaligned_be32(dev->se_sub_dev->se_dev_attrib.max_sectors, &buf[8]);
+	put_unaligned_be32(dev->se_sub_dev->se_dev_attrib.fabric_max_sectors, &buf[8]);
 
 	/*
 	 * Set OPTIMAL TRANSFER LENGTH

drivers/target/target_core_configfs.c

@@ -702,6 +702,9 @@ SE_DEV_ATTR_RO(hw_max_sectors);
 DEF_DEV_ATTRIB(max_sectors);
 SE_DEV_ATTR(max_sectors, S_IRUGO | S_IWUSR);
 
+DEF_DEV_ATTRIB(fabric_max_sectors);
+SE_DEV_ATTR(fabric_max_sectors, S_IRUGO | S_IWUSR);
+
 DEF_DEV_ATTRIB(optimal_sectors);
 SE_DEV_ATTR(optimal_sectors, S_IRUGO | S_IWUSR);
 
@@ -741,6 +744,7 @@ static struct configfs_attribute *target_core_dev_attrib_attrs[] = {
 	&target_core_dev_attrib_block_size.attr,
 	&target_core_dev_attrib_hw_max_sectors.attr,
 	&target_core_dev_attrib_max_sectors.attr,
+	&target_core_dev_attrib_fabric_max_sectors.attr,
 	&target_core_dev_attrib_optimal_sectors.attr,
 	&target_core_dev_attrib_hw_queue_depth.attr,
 	&target_core_dev_attrib_queue_depth.attr,

drivers/target/target_core_device.c

@@ -889,10 +889,15 @@ void se_dev_set_default_attribs(
 						limits->logical_block_size);
 	dev->se_sub_dev->se_dev_attrib.max_sectors = limits->max_sectors;
 	/*
-	 * Set optimal_sectors from max_sectors, which can be lowered via
-	 * configfs.
+	 * Set fabric_max_sectors, which is reported in block limits
+	 * VPD page (B0h).
 	 */
-	dev->se_sub_dev->se_dev_attrib.optimal_sectors = limits->max_sectors;
+	dev->se_sub_dev->se_dev_attrib.fabric_max_sectors = DA_FABRIC_MAX_SECTORS;
+	/*
+	 * Set optimal_sectors from fabric_max_sectors, which can be
+	 * lowered via configfs.
+	 */
+	dev->se_sub_dev->se_dev_attrib.optimal_sectors = DA_FABRIC_MAX_SECTORS;
 	/*
 	 * queue_depth is based on subsystem plugin dependent requirements.
 	 */
@@ -1224,6 +1229,54 @@ int se_dev_set_max_sectors(struct se_device *dev, u32 max_sectors)
 	return 0;
 }
 
+int se_dev_set_fabric_max_sectors(struct se_device *dev, u32 fabric_max_sectors)
+{
+	if (atomic_read(&dev->dev_export_obj.obj_access_count)) {
+		pr_err("dev[%p]: Unable to change SE Device"
+			" fabric_max_sectors while dev_export_obj: %d count exists\n",
+			dev, atomic_read(&dev->dev_export_obj.obj_access_count));
+		return -EINVAL;
+	}
+	if (!fabric_max_sectors) {
+		pr_err("dev[%p]: Illegal ZERO value for"
+			" fabric_max_sectors\n", dev);
+		return -EINVAL;
+	}
+	if (fabric_max_sectors < DA_STATUS_MAX_SECTORS_MIN) {
+		pr_err("dev[%p]: Passed fabric_max_sectors: %u less than"
+			" DA_STATUS_MAX_SECTORS_MIN: %u\n", dev, fabric_max_sectors,
+				DA_STATUS_MAX_SECTORS_MIN);
+		return -EINVAL;
+	}
+	if (dev->transport->transport_type == TRANSPORT_PLUGIN_PHBA_PDEV) {
+		if (fabric_max_sectors > dev->se_sub_dev->se_dev_attrib.hw_max_sectors) {
+			pr_err("dev[%p]: Passed fabric_max_sectors: %u"
+				" greater than TCM/SE_Device max_sectors:"
+				" %u\n", dev, fabric_max_sectors,
+				dev->se_sub_dev->se_dev_attrib.hw_max_sectors);
+			 return -EINVAL;
+		}
+	} else {
+		if (fabric_max_sectors > DA_STATUS_MAX_SECTORS_MAX) {
+			pr_err("dev[%p]: Passed fabric_max_sectors: %u"
+				" greater than DA_STATUS_MAX_SECTORS_MAX:"
+				" %u\n", dev, fabric_max_sectors,
+				DA_STATUS_MAX_SECTORS_MAX);
+			return -EINVAL;
+		}
+	}
+	/*
+	 * Align max_sectors down to PAGE_SIZE to follow transport_allocate_data_tasks()
+	 */
+	fabric_max_sectors = se_dev_align_max_sectors(fabric_max_sectors,
+						      dev->se_sub_dev->se_dev_attrib.block_size);
+
+	dev->se_sub_dev->se_dev_attrib.fabric_max_sectors = fabric_max_sectors;
+	pr_debug("dev[%p]: SE Device max_sectors changed to %u\n",
+			dev, fabric_max_sectors);
+	return 0;
+}
+
 int se_dev_set_optimal_sectors(struct se_device *dev, u32 optimal_sectors)
 {
 	if (atomic_read(&dev->dev_export_obj.obj_access_count)) {
@@ -1237,10 +1290,10 @@ int se_dev_set_optimal_sectors(struct se_device *dev, u32 optimal_sectors)
 				" changed for TCM/pSCSI\n", dev);
 		return -EINVAL;
 	}
-	if (optimal_sectors > dev->se_sub_dev->se_dev_attrib.max_sectors) {
+	if (optimal_sectors > dev->se_sub_dev->se_dev_attrib.fabric_max_sectors) {
 		pr_err("dev[%p]: Passed optimal_sectors %u cannot be"
-			" greater than max_sectors: %u\n", dev,
-			optimal_sectors, dev->se_sub_dev->se_dev_attrib.max_sectors);
+			" greater than fabric_max_sectors: %u\n", dev,
+			optimal_sectors, dev->se_sub_dev->se_dev_attrib.fabric_max_sectors);
 		return -EINVAL;
 	}
 

drivers/target/target_core_internal.h

@@ -53,6 +53,7 @@ int	se_dev_set_is_nonrot(struct se_device *, int);
 int	se_dev_set_emulate_rest_reord(struct se_device *dev, int);
 int	se_dev_set_queue_depth(struct se_device *, u32);
 int	se_dev_set_max_sectors(struct se_device *, u32);
+int	se_dev_set_fabric_max_sectors(struct se_device *, u32);
 int	se_dev_set_optimal_sectors(struct se_device *, u32);
 int	se_dev_set_block_size(struct se_device *, u32);
 struct se_lun *core_dev_add_lun(struct se_portal_group *, struct se_hba *,

drivers/target/target_core_transport.c

@@ -37,6 +37,7 @@
 #include <linux/in.h>
 #include <linux/cdrom.h>
 #include <linux/module.h>
+#include <linux/ratelimit.h>
 #include <asm/unaligned.h>
 #include <net/sock.h>
 #include <net/tcp.h>
@@ -3107,6 +3108,13 @@ static int transport_generic_cmd_sequencer(
 		cmd->data_length = size;
 	}
 
+	if (cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB &&
+	    sectors > dev->se_sub_dev->se_dev_attrib.fabric_max_sectors) {
+		printk_ratelimited(KERN_ERR "SCSI OP %02xh with too big sectors %u\n",
+				   cdb[0], sectors);
+		goto out_invalid_cdb_field;
+	}
+
 	/* reject any command that we don't have a handler for */
 	if (!(passthrough || cmd->execute_task ||
 	     (cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB)))

include/target/target_core_base.h

@@ -86,6 +86,8 @@
 #define DA_UNMAP_GRANULARITY_DEFAULT		0
 /* Default unmap_granularity_alignment */
 #define DA_UNMAP_GRANULARITY_ALIGNMENT_DEFAULT	0
+/* Default max transfer length */
+#define DA_FABRIC_MAX_SECTORS			8192
 /* Emulation for Direct Page Out */
 #define DA_EMULATE_DPO				0
 /* Emulation for Forced Unit Access WRITEs */
@@ -726,6 +728,7 @@ struct se_dev_attrib {
 	u32		block_size;
 	u32		hw_max_sectors;
 	u32		max_sectors;
+	u32		fabric_max_sectors;
 	u32		optimal_sectors;
 	u32		hw_queue_depth;
 	u32		queue_depth;