scsi: target: iblock: Allow iblock devices to be shared

We might be running a local application that also interacts with the
backing device. In this setup we have some clustering type of software
that manages the ownwer of it, so we don't want the kernel to restrict
us. This patch allows the user to control if the driver gets exclusive
access.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20250721185145.20913-1-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: mikechristie

drivers/target/target_core_iblock.c

@@ -64,6 +64,7 @@ static struct se_device *iblock_alloc_device(struct se_hba *hba, const char *nam
 		pr_err("Unable to allocate struct iblock_dev\n");
 		return NULL;
 	}
+	ib_dev->ibd_exclusive = true;
 
 	ib_dev->ibd_plug = kcalloc(nr_cpu_ids, sizeof(*ib_dev->ibd_plug),
 				   GFP_KERNEL);
@@ -95,6 +96,7 @@ static int iblock_configure_device(struct se_device *dev)
 	struct block_device *bd;
 	struct blk_integrity *bi;
 	blk_mode_t mode = BLK_OPEN_READ;
+	void *holder = ib_dev;
 	unsigned int max_write_zeroes_sectors;
 	int ret;
 
@@ -109,15 +111,18 @@ static int iblock_configure_device(struct se_device *dev)
 		goto out;
 	}
 
-	pr_debug( "IBLOCK: Claiming struct block_device: %s\n",
-			ib_dev->ibd_udev_path);
+	pr_debug("IBLOCK: Claiming struct block_device: %s: %d\n",
+		 ib_dev->ibd_udev_path, ib_dev->ibd_exclusive);
 
 	if (!ib_dev->ibd_readonly)
 		mode |= BLK_OPEN_WRITE;
 	else
 		dev->dev_flags |= DF_READ_ONLY;
 
-	bdev_file = bdev_file_open_by_path(ib_dev->ibd_udev_path, mode, ib_dev,
+	if (!ib_dev->ibd_exclusive)
+		holder = NULL;
+
+	bdev_file = bdev_file_open_by_path(ib_dev->ibd_udev_path, mode, holder,
 					NULL);
 	if (IS_ERR(bdev_file)) {
 		ret = PTR_ERR(bdev_file);
@@ -560,13 +565,14 @@ iblock_execute_write_same(struct se_cmd *cmd)
 }
 
 enum {
-	Opt_udev_path, Opt_readonly, Opt_force, Opt_err
+	Opt_udev_path, Opt_readonly, Opt_force, Opt_exclusive, Opt_err,
 };
 
 static match_table_t tokens = {
 	{Opt_udev_path, "udev_path=%s"},
 	{Opt_readonly, "readonly=%d"},
 	{Opt_force, "force=%d"},
+	{Opt_exclusive, "exclusive=%d"},
 	{Opt_err, NULL}
 };
 
@@ -576,7 +582,7 @@ static ssize_t iblock_set_configfs_dev_params(struct se_device *dev,
 	struct iblock_dev *ib_dev = IBLOCK_DEV(dev);
 	char *orig, *ptr, *arg_p, *opts;
 	substring_t args[MAX_OPT_ARGS];
-	int ret = 0, token;
+	int ret = 0, token, tmp_exclusive;
 	unsigned long tmp_readonly;
 
 	opts = kstrdup(page, GFP_KERNEL);
@@ -623,6 +629,22 @@ static ssize_t iblock_set_configfs_dev_params(struct se_device *dev,
 			ib_dev->ibd_readonly = tmp_readonly;
 			pr_debug("IBLOCK: readonly: %d\n", ib_dev->ibd_readonly);
 			break;
+		case Opt_exclusive:
+			arg_p = match_strdup(&args[0]);
+			if (!arg_p) {
+				ret = -ENOMEM;
+				break;
+			}
+			ret = kstrtoint(arg_p, 0, &tmp_exclusive);
+			kfree(arg_p);
+			if (ret < 0) {
+				pr_err("kstrtoul() failed for exclusive=\n");
+				goto out;
+			}
+			ib_dev->ibd_exclusive = tmp_exclusive;
+			pr_debug("IBLOCK: exclusive: %d\n",
+				 ib_dev->ibd_exclusive);
+			break;
 		case Opt_force:
 			break;
 		default:
@@ -647,6 +669,7 @@ static ssize_t iblock_show_configfs_dev_params(struct se_device *dev, char *b)
 		bl += sprintf(b + bl, "  UDEV PATH: %s",
 				ib_dev->ibd_udev_path);
 	bl += sprintf(b + bl, "  readonly: %d\n", ib_dev->ibd_readonly);
+	bl += sprintf(b + bl, "  exclusive: %d\n", ib_dev->ibd_exclusive);
 
 	bl += sprintf(b + bl, "        ");
 	if (bd) {

drivers/target/target_core_iblock.h

@@ -34,6 +34,7 @@ struct iblock_dev {
 	struct block_device *ibd_bd;
 	struct file *ibd_bdev_file;
 	bool ibd_readonly;
+	bool ibd_exclusive;
 	struct iblock_dev_plug *ibd_plug;
 } ____cacheline_aligned;