This target allows you to map in a region of another device as a
contiguous range of blocks of a dm device.
This is the basic building block used by LVM to stitch together
logical volumes from one or more ranges of blocks from one or more
physical disks.
Signed-off-by: Tobias Waldekranz <tob...@waldekranz.com>
---
Notes:
v1 -> v2:
- Propagate errors from lower devices
- Whitespace
drivers/block/dm/Kconfig | 6 ++
drivers/block/dm/Makefile | 1 +
drivers/block/dm/dm-linear.c | 129 +++++++++++++++++++++++++++++++++++
3 files changed, 136 insertions(+)
create mode 100644 drivers/block/dm/dm-linear.c
diff --git a/drivers/block/dm/Kconfig b/drivers/block/dm/Kconfig
index 3316386d0c..03a0876eda 100644
--- a/drivers/block/dm/Kconfig
+++ b/drivers/block/dm/Kconfig
@@ -5,3 +5,9 @@ menuconfig DM_BLK
other data sources. Modeled after, and intended to be
compatible with, the Linux kernel's device mapper subsystem.
+config DM_BLK_LINEAR
+ bool "Linear target"
+ depends on DM_BLK
+ help
+ Maps a contiguous region of an existing device into a dm
+ device.
diff --git a/drivers/block/dm/Makefile b/drivers/block/dm/Makefile
index 9c045087c0..f52d19f9c4 100644
--- a/drivers/block/dm/Makefile
+++ b/drivers/block/dm/Makefile
@@ -1,2 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only
obj-$(CONFIG_DM_BLK) += dm-core.o
+obj-$(CONFIG_DM_BLK_LINEAR) += dm-linear.o
diff --git a/drivers/block/dm/dm-linear.c b/drivers/block/dm/dm-linear.c
new file mode 100644
index 0000000000..797d761f63
--- /dev/null
+++ b/drivers/block/dm/dm-linear.c
@@ -0,0 +1,129 @@
+// SPDX-License-Identifier: GPL-2.0-only
+// SPDX-FileCopyrightText: © 2025 Tobias Waldekranz <tob...@waldekranz.com>,
Wires
+
+#include <block.h>
+#include <disks.h>
+#include <fcntl.h>
+#include <xfuncs.h>
+
+#include <linux/kstrtox.h>
+
+#include "dm-target.h"
+
+struct dm_linear {
+ struct cdev *cdev;
+ loff_t offset;
+};
+
+static int dm_linear_read(struct dm_target *ti, void *buf,
+ sector_t block, blkcnt_t num_blocks)
+{
+ struct dm_linear *l = ti->private;
+ ssize_t ret;
+
+ block <<= SECTOR_SHIFT;
+ num_blocks <<= SECTOR_SHIFT;
+
+ ret = cdev_read(l->cdev, buf, num_blocks, l->offset + block, 0);
+ if (ret < num_blocks)
+ return (ret < 0) ? ret : -EIO;
+
+ return 0;
+}
+
+static int dm_linear_write(struct dm_target *ti, const void *buf,
+ sector_t block, blkcnt_t num_blocks)
+{
+ struct dm_linear *l = ti->private;
+ ssize_t ret;
+
+ block <<= SECTOR_SHIFT;
+ num_blocks <<= SECTOR_SHIFT;
+
+ ret = cdev_write(l->cdev, buf, num_blocks, l->offset + block, 0);
+ if (ret < num_blocks)
+ return (ret < 0) ? ret : -EIO;
+
+ return 0;
+}
+
+static int dm_linear_create(struct dm_target *ti, unsigned int argc, char
**argv)
+{
+ struct dm_linear *l;
+ int err;
+
+ if (argc != 2) {
+ dm_target_err(ti, "Expected 2 arguments (\"<dev> <offset>\"),
got %u\n",
+ argc);
+ err = -EINVAL;
+ goto err;
+ }
+
+ l = xzalloc(sizeof(*l));
+ ti->private = l;
+
+ if (kstrtoull(argv[1], 0, &l->offset)) {
+ dm_target_err(ti, "Invalid offset: \"%s\"\n", argv[1]);
+ err = -EINVAL;
+ goto err_free;
+ }
+ l->offset <<= SECTOR_SHIFT;
+
+ l->cdev = cdev_open_by_path_name(argv[0], O_RDWR);
+ if (!l->cdev) {
+ dm_target_err(ti, "Cannot open device %s: %m\n", argv[0]);
+ err = -ENODEV;
+ goto err_free;
+ }
+
+ l->cdev = cdev_readlink(l->cdev);
+
+ if ((ti->size << SECTOR_SHIFT) > (l->cdev->size - l->offset)) {
+ dm_target_err(ti, "%s is too small to map %llu blocks at %llu,
%llu available\n",
+ argv[0], ti->size, l->offset >> SECTOR_SHIFT,
+ (l->cdev->size - l->offset) >> SECTOR_SHIFT);
+ err = -ENOSPC;
+ goto err_close;
+ }
+
+ return 0;
+
+err_close:
+ cdev_close(l->cdev);
+err_free:
+ free(l);
+err:
+ return err;
+}
+
+static int dm_linear_destroy(struct dm_target *ti)
+{
+ struct dm_linear *l = ti->private;
+
+ cdev_close(l->cdev);
+ free(l);
+ return 0;
+}
+
+static char *dm_linear_asprint(struct dm_target *ti)
+{
+ struct dm_linear *l = ti->private;
+
+ return xasprintf("dev:%s offset:%llu",
+ cdev_name(l->cdev), l->offset >> SECTOR_SHIFT);
+}
+
+static struct dm_target_ops dm_linear_ops = {
+ .name = "linear",
+ .asprint = dm_linear_asprint,
+ .create = dm_linear_create,
+ .destroy = dm_linear_destroy,
+ .read = dm_linear_read,
+ .write = dm_linear_write,
+};
+
+static int __init dm_linear_init(void)
+{
+ return dm_target_register(&dm_linear_ops);
+}
+device_initcall(dm_linear_init);
--
2.43.0
