scsi: target: Split out COMPARE AND WRITE memcmp into helper

In preparation for finding and returning the miscompare offset.

Link: https://lore.kernel.org/r/20201031233211.5207-4-ddiss@suse.deReviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_sbc.c

@@ -434,20 +434,75 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success,
 	return ret;
 }
 
+/*
+ * compare @cmp_len bytes of @read_sgl with @cmp_sgl. On miscompare return
+ * TCM_MISCOMPARE_VERIFY.
+ */
+static sense_reason_t
+compare_and_write_do_cmp(struct scatterlist *read_sgl, unsigned int read_nents,
+			 struct scatterlist *cmp_sgl, unsigned int cmp_nents,
+			 unsigned int cmp_len)
+{
+	unsigned char *buf = NULL;
+	struct scatterlist *sg;
+	sense_reason_t ret;
+	unsigned int offset;
+	size_t rc;
+	int i;
+
+	buf = kzalloc(cmp_len, GFP_KERNEL);
+	if (!buf) {
+		ret = TCM_OUT_OF_RESOURCES;
+		goto out;
+	}
+
+	rc = sg_copy_to_buffer(cmp_sgl, cmp_nents, buf, cmp_len);
+	if (!rc) {
+		pr_err("sg_copy_to_buffer() failed for compare_and_write\n");
+		ret = TCM_OUT_OF_RESOURCES;
+		goto out;
+	}
+	/*
+	 * Compare SCSI READ payload against verify payload
+	 */
+	offset = 0;
+	for_each_sg(read_sgl, sg, read_nents, i) {
+		unsigned int len = min(sg->length, cmp_len);
+		unsigned char *addr = kmap_atomic(sg_page(sg));
+
+		if (memcmp(addr, buf + offset, len)) {
+			pr_warn("Detected MISCOMPARE for addr: %p buf: %p\n",
+				addr, buf + offset);
+			kunmap_atomic(addr);
+			ret = TCM_MISCOMPARE_VERIFY;
+			goto out;
+		}
+		kunmap_atomic(addr);
+
+		offset += len;
+		cmp_len -= len;
+		if (!cmp_len)
+			break;
+	}
+	pr_debug("COMPARE AND WRITE read data matches compare data\n");
+	ret = TCM_NO_SENSE;
+out:
+	kfree(buf);
+	return ret;
+}
+
 static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success,
 						 int *post_ret)
 {
 	struct se_device *dev = cmd->se_dev;
 	struct sg_table write_tbl = { };
-	struct scatterlist *write_sg, *sg;
-	unsigned char *buf = NULL, *addr;
+	struct scatterlist *write_sg;
 	struct sg_mapping_iter m;
-	unsigned int offset = 0, len;
-	unsigned int nlbas = cmd->t_task_nolb;
+	unsigned int len;
 	unsigned int block_size = dev->dev_attrib.block_size;
-	unsigned int compare_len = (nlbas * block_size);
+	unsigned int compare_len = (cmd->t_task_nolb * block_size);
 	sense_reason_t ret = TCM_NO_SENSE;
-	int rc, i;
+	int i;
 
 	/*
 	 * Handle early failure in transport_generic_request_failure(),
@@ -473,12 +528,13 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
 		goto out;
 	}
 
-	buf = kzalloc(cmd->data_length, GFP_KERNEL);
-	if (!buf) {
-		pr_err("Unable to allocate compare_and_write buf\n");
-		ret = TCM_OUT_OF_RESOURCES;
+	ret = compare_and_write_do_cmp(cmd->t_bidi_data_sg,
+				       cmd->t_bidi_data_nents,
+				       cmd->t_data_sg,
+				       cmd->t_data_nents,
+				       compare_len);
+	if (ret)
 		goto out;
-	}
 
 	if (sg_alloc_table(&write_tbl, cmd->t_data_nents, GFP_KERNEL) < 0) {
 		pr_err("Unable to allocate compare_and_write sg\n");
@@ -486,44 +542,9 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
 		goto out;
 	}
 	write_sg = write_tbl.sgl;
-	/*
-	 * Setup verify and write data payloads from total NumberLBAs.
-	 */
-	rc = sg_copy_to_buffer(cmd->t_data_sg, cmd->t_data_nents, buf,
-			       cmd->data_length);
-	if (!rc) {
-		pr_err("sg_copy_to_buffer() failed for compare_and_write\n");
-		ret = TCM_OUT_OF_RESOURCES;
-		goto out;
-	}
-	/*
-	 * Compare against SCSI READ payload against verify payload
-	 */
-	for_each_sg(cmd->t_bidi_data_sg, sg, cmd->t_bidi_data_nents, i) {
-		addr = (unsigned char *)kmap_atomic(sg_page(sg));
-		if (!addr) {
-			ret = TCM_OUT_OF_RESOURCES;
-			goto out;
-		}
-
-		len = min(sg->length, compare_len);
-
-		if (memcmp(addr, buf + offset, len)) {
-			pr_warn("Detected MISCOMPARE for addr: %p buf: %p\n",
-				addr, buf + offset);
-			kunmap_atomic(addr);
-			goto miscompare;
-		}
-		kunmap_atomic(addr);
-
-		offset += len;
-		compare_len -= len;
-		if (!compare_len)
-			break;
-	}
 
 	i = 0;
-	len = cmd->t_task_nolb * block_size;
+	len = compare_len;
 	sg_miter_start(&m, cmd->t_data_sg, cmd->t_data_nents, SG_MITER_TO_SG);
 	/*
 	 * Currently assumes NoLB=1 and SGLs are PAGE_SIZE..
@@ -568,13 +589,8 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
 
 	__target_execute_cmd(cmd, false);
 
-	kfree(buf);
 	return ret;
 
-miscompare:
-	pr_warn("Target/%s: Send MISCOMPARE check condition and sense\n",
-		dev->transport->name);
-	ret = TCM_MISCOMPARE_VERIFY;
 out:
 	/*
 	 * In the MISCOMPARE or failure case, unlock ->caw_sem obtained in
@@ -582,7 +598,6 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool succes
 	 */
 	up(&dev->caw_sem);
 	sg_free_table(&write_tbl);
-	kfree(buf);
 	return ret;
 }