From: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
This new target is similar to the linear target except that it emulates
a smaller logical block size on devices with larger ones. It's main
purpose is to emulate 512 byte sectors on 4K native disks (i.e. 512e).
See Documentation/admin-guide/device-mapper/dm-ebs.rst for details.
Changes versus version 1 sent on 2/10/2020:
- allow larger underlying block size
- prefetch buffers for mis-aligned writes
- format issues and typos
Signed-off-by: Heinz Mauelshagen <heinzm@xxxxxxxxxx>
---
.../admin-guide/device-mapper/dm-ebs.rst | 49 ++
drivers/md/Kconfig | 8 +
drivers/md/Makefile | 2 +
drivers/md/dm-ebs-target.c | 425 ++++++++++++++++++
4 files changed, 484 insertions(+)
create mode 100644 Documentation/admin-guide/device-mapper/dm-ebs.rst
create mode 100644 drivers/md/dm-ebs-target.c
diff --git a/Documentation/admin-guide/device-mapper/dm-ebs.rst b/Documentation/admin-guide/device-mapper/dm-ebs.rst
new file mode 100644
index 000000000000..530771dbb352
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/dm-ebs.rst
@@ -0,0 +1,49 @@
+======
+dm-ebs
+======
+
+This target is similar to the linear target except that it emulates
+smaller logical block size on devices with larger ones. It's main
+purpose is to emulate 512 byte sectors on 4K native disks (i.e 512e).
+
+Supported emulated logical block sizes 512, 1024, 2048 and 4096.
+
+Underlying block size can be set to > 4K to test buffering larger units.
+
+
+Table parameters
+----------------
+ <dev path> <offset> <emulated sectors> [<underlying sectors>]
+
+Mandatory parameters:
+
+ <dev path>:
+ Full pathname to the underlying block-device,
+ or a "major:minor" device-number.
+ <offset>:
+ Starting sector within the device;
+ has to be a multiple of <emulated sectors>.
+ <emulated sectors>:
+ Number of sectors defining the logical block size to be emulated;
+ 1, 2, 4, 8 sectors of 512 bytes supported.
+
+Optional parameter:
+
+ <underyling sectors>:
+ Number of sectors defining the logical block size of <dev path>.
+ 2^N supported, e.g. 8 = emulate 8 sectors of 512 bytes = 4KiB.
+ If not provided, the logical block size of <dev path> will be used.
+
+
+Examples:
+
+Emulate 1 sector = 512 bytes logical block size on /dev/sda starting at
+offset 1024 sectors with underlying devices block size automatically set:
+
+ebs /dev/sda 1024 1
+
+Emulate 2 sector = 1KiB logical block size on /dev/sda starting at
+offset 128 sectors, enforce 2KiB underlying device block size.
+This presumes 2KiB logical blocksize on /dev/sda or less to work:
+
+ebs /dev/sda 128 2 4
diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
index d6d5ab23c088..392974a2999d 100644
--- a/drivers/md/Kconfig
+++ b/drivers/md/Kconfig
@@ -336,6 +336,14 @@ config DM_WRITECACHE
The writecache target doesn't cache reads because reads are supposed
to be cached in standard RAM.
+config DM_EBS
+ tristate "Emulated block size target (EXPERIMENTAL)"
+ depends on BLK_DEV_DM
+ default n
+ ---help---
+ dm-ebs emulates smaller logical block size on backing devices
+ with larger ones (e.g. 512 byte sectors on 4K native disks).
+
config DM_ERA
tristate "Era target (EXPERIMENTAL)"
depends on BLK_DEV_DM
diff --git a/drivers/md/Makefile b/drivers/md/Makefile
index d91a7edcd2ab..9a2d673f94bc 100644
--- a/drivers/md/Makefile
+++ b/drivers/md/Makefile
@@ -17,6 +17,7 @@ dm-thin-pool-y += dm-thin.o dm-thin-metadata.o
dm-cache-y += dm-cache-target.o dm-cache-metadata.o dm-cache-policy.o \
dm-cache-background-tracker.o
dm-cache-smq-y += dm-cache-policy-smq.o
+dm-ebs-y += dm-ebs-target.o
dm-era-y += dm-era-target.o
dm-clone-y += dm-clone-target.o dm-clone-metadata.o
dm-verity-y += dm-verity-target.o
@@ -65,6 +66,7 @@ obj-$(CONFIG_DM_THIN_PROVISIONING) += dm-thin-pool.o
obj-$(CONFIG_DM_VERITY) += dm-verity.o
obj-$(CONFIG_DM_CACHE) += dm-cache.o
obj-$(CONFIG_DM_CACHE_SMQ) += dm-cache-smq.o
+obj-$(CONFIG_DM_EBS) += dm-ebs.o
obj-$(CONFIG_DM_ERA) += dm-era.o
obj-$(CONFIG_DM_CLONE) += dm-clone.o
obj-$(CONFIG_DM_LOG_WRITES) += dm-log-writes.o
diff --git a/drivers/md/dm-ebs-target.c b/drivers/md/dm-ebs-target.c
new file mode 100644
index 000000000000..1439bcece6fd
--- /dev/null
+++ b/drivers/md/dm-ebs-target.c
@@ -0,0 +1,425 @@
+/*
+ * Copyright (C) 2020 Red Hat GmbH
+ *
+ * This file is released under the GPL.
+ *
+ * Device-mapper target to emulate smaller logical block
+ * size on backing devices exposing (natively) larger ones.
+ *
+ * E.g. 512 byte sector emulation on 4K native disks.
+ */
+
+#include "dm.h"
+#include <linux/module.h>
+#include <linux/workqueue.h>
+#include <linux/dm-bufio.h>
+
+#define DM_MSG_PREFIX "ebs"
+
+static void ebs_dtr(struct dm_target *ti);
+
+/* Emulated block size context. */
+struct ebs_c {
+ struct dm_dev *dev;
+ struct dm_bufio_client *bufio;
+ struct work_struct ws;
+ struct workqueue_struct *wq;
+ struct bio_list bios_in;
+ spinlock_t lock; /* Guard bios_in list above */
+ sector_t start;
+ unsigned int ebs;
+ unsigned int ubs;
+ unsigned char shift;
+ unsigned short ubs_set:1;
+};
+
+static sector_t __sector_to_block(struct ebs_c *ec, sector_t sector)
+{
+ return sector >> ec->shift;
+}
+
+static sector_t __block_mod(sector_t sector, unsigned int bs)
+{
+ return sector & (bs - 1);
+}
+
+/* Return number of blocks for a bio */
+static unsigned int __nr_blocks(struct ebs_c *ec, struct bio *bio)
+{
+ sector_t end_sector = __block_mod(bio->bi_iter.bi_sector, ec->ubs) + bio_sectors(bio);
+
+ return __sector_to_block(ec, end_sector) + __block_mod(end_sector, ec->ubs) ? 1 : 0;
+}
+
+static bool __ebs_check_bs(unsigned int bs)
+{
+ return bs && is_power_of_2(bs);
+}
+
+/* READ/WRITE bio vector: copy blocks between bufio blocks and bio vector's (partial/overlapping) pages. */
+static int __ebs_rw_bvec(struct ebs_c *ec, int rw, struct bio_vec *bv, struct bvec_iter *iter)
+{
+ int r = 0;
+ unsigned char *ba, *pa = page_address(bv->bv_page) + bv->bv_offset;
+ unsigned int cur_len;
+ unsigned int bv_len = bv->bv_len;
+ unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->ubs));
+ sector_t block = __sector_to_block(ec, iter->bi_sector);
+ struct dm_buffer *b;
+
+ if (!bv->bv_page || !bv_len)
+ return -EIO;
+
+ /* Handle overlapping page <-> blocks */
+ while (bv_len) {
+ cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);
+
+ /* Avoid reading for writes in case bio vector's page overwrites block completely. */
+ if (rw == READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
+ ba = dm_bufio_read(ec->bufio, block, &b);
+ else
+ ba = dm_bufio_new(ec->bufio, block, &b);
+
+ if (unlikely(IS_ERR(ba)))
+ r = PTR_ERR(ba); /* Carry on with next buffer if any but return error. */
+ else {
+ /* Copy data to/from bio to buffer if read/new was successful above. */
+ ba += buf_off;
+ if (rw == READ)
+ memcpy(pa, ba, cur_len);
+ else {
+ memcpy(ba, pa, cur_len);
+ dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len);
+ }
+
+ dm_bufio_release(b);
+ }
+
+ pa += cur_len;
+ bv_len -= cur_len;
+ buf_off = 0;
+ block++;
+ }
+
+ return r;
+}
+
+/* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
+static int __ebs_rw_bio(struct ebs_c *ec, int rw, struct bio *bio)
+{
+ int r = 0, rr;
+ struct bio_vec bv;
+ struct bvec_iter iter;
+
+ bio_for_each_bvec(bv, bio, iter) {
+ rr = __ebs_rw_bvec(ec, rw, &bv, &iter);
+ if (rr)
+ r = rr;
+ }
+
+ return r;
+}
+
+/* 'Discard' blocks, i.e. release them from the bufio cache. */
+static int __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
+{
+ sector_t end = bio_end_sector(bio), sector;
+
+ for (sector = bio->bi_iter.bi_sector; sector < end; sector += ec->ubs)
+ dm_bufio_forget(ec->bufio, __sector_to_block(ec, sector));
+
+ return 0;
+}
+
+/* Worker funtion to process incoming bios. */
+static void __ebs_process_bios(struct work_struct *ws)
+{
+ int r;
+ bool write = false;
+ struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
+ struct bio *bio;
+ struct bio_list bios;
+
+ bio_list_init(&bios);
+
+ spin_lock_irq(&ec->lock);
+ bios = ec->bios_in;
+ bio_list_init(&ec->bios_in);
+ spin_unlock_irq(&ec->lock);
+
+ /* Prefetch all read and any mis-aligned write buffers */
+ bio_list_for_each(bio, &bios) {
+ if (bio_op(bio) == REQ_OP_READ)
+ dm_bufio_prefetch(ec->bufio, __sector_to_block(ec, bio->bi_iter.bi_sector), __nr_blocks(ec, bio));
+ else if (bio_op(bio) == REQ_OP_WRITE) {
+ if (__block_mod(bio->bi_iter.bi_sector, ec->ubs))
+ dm_bufio_prefetch(ec->bufio, __sector_to_block(ec, bio->bi_iter.bi_sector), 1);
+ if (__block_mod(bio_end_sector(bio), ec->ubs))
+ dm_bufio_prefetch(ec->bufio, __sector_to_block(ec, bio_end_sector(bio)), 1);
+ }
+ }
+
+ bio_list_for_each(bio, &bios) {
+ r = -EIO;
+
+ if (bio_op(bio) == REQ_OP_READ)
+ r = __ebs_rw_bio(ec, READ, bio);
+ else if (bio_op(bio) == REQ_OP_WRITE) {
+ write = true;
+ r = __ebs_rw_bio(ec, WRITE, bio);
+ } else if (bio_op(bio) == REQ_OP_DISCARD)
+ /* FIXME: call dm_bufio_discard_buffers() once upstream. */
+ r = __ebs_forget_bio(ec, bio);
+
+ if (r)
+ bio->bi_status = BLK_STS_IOERR;
+ }
+
+ r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;
+
+ while ((bio = bio_list_pop(&bios))) {
+ /* FIXME: any other request is just endioed for now. */
+ if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
+ bio_io_error(bio);
+ else
+ bio_endio(bio);
+ }
+}
+
+/*
+ * Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
+ *
+ * <dev_path>: path of the underlying device
+ * <offset>: offset in 512 bytes sectors into <dev_path>
+ * <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
+ * [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
+ * optional, if not supplied, retrieve logical block size from underlying device
+ */
+static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+ int r;
+ unsigned short tmp1;
+ unsigned long long tmp;
+ char dummy;
+ struct ebs_c *ec;
+
+ if (argc < 3 || argc > 4) {
+ ti->error = "Invalid argument count";
+ return -EINVAL;
+ }
+
+ ec = ti->private = kzalloc(sizeof(*ec), GFP_KERNEL);
+ if (!ec) {
+ ti->error = "Cannot allocate ebs context";
+ return -ENOMEM;
+ }
+
+ r = -EINVAL;
+ if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
+ tmp != (sector_t)tmp ||
+ (sector_t)tmp >= ti->len) {
+ ti->error = "Invalid device offset sector";
+ goto bad;
+ }
+ ec->start = tmp;
+
+ if (sscanf(argv[2], "%hu%c", &tmp1, &dummy) != 1 ||
+ !__ebs_check_bs(tmp1) ||
+ to_bytes(tmp1) > PAGE_SIZE) {
+ ti->error = "Invalid emulated block size";
+ goto bad;
+ }
+ ec->ebs = tmp1;
+
+ if (argc > 3) {
+ if (sscanf(argv[3], "%hu%c", &tmp1, &dummy) != 1 || !__ebs_check_bs(tmp1)) {
+ ti->error = "Invalid underlying block size";
+ goto bad;
+ }
+ ec->ubs = tmp1;
+ ec->ubs_set = true;
+ } else
+ ec->ubs_set = false;
+
+ r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &ec->dev);
+ if (r) {
+ ti->error = "Device lookup failed";
+ ec->dev = NULL;
+ goto bad;
+ }
+
+ r = -EINVAL;
+ if (!ec->ubs_set) {
+ ec->ubs = to_sector(bdev_logical_block_size(ec->dev->bdev));
+ if (!__ebs_check_bs(ec->ubs)) {
+ ti->error = "Invalid retrieved underlying block size";
+ goto bad;
+ }
+ }
+
+ if (!ec->ubs_set && ec->ebs == ec->ubs)
+ DMERR("Emulation superfluous: emulated equal to underlying block size");
+
+ if (__block_mod(ec->start, ec->ubs)) {
+ ti->error = "Device offset must be multiple of underlying block size";
+ goto bad;
+ }
+
+ ec->bufio = dm_bufio_client_create(ec->dev->bdev, to_bytes(ec->ubs), 1, 0, NULL, NULL);
+ if (IS_ERR(ec->bufio)) {
+ ti->error = "Cannot create dm bufio client";
+ r = PTR_ERR(ec->bufio);
+ ec->bufio = NULL;
+ goto bad;
+ }
+
+ ec->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
+ if (!ec->wq) {
+ ti->error = "Cannot create dm-" DM_MSG_PREFIX " workqueue";
+ r = -ENOMEM;
+ goto bad;
+ }
+
+ ec->shift = __ffs(ec->ubs);
+ INIT_WORK(&ec->ws, &__ebs_process_bios);
+ bio_list_init(&ec->bios_in);
+ spin_lock_init(&ec->lock);
+
+ ti->num_flush_bios = 1;
+ ti->num_discard_bios = 1;
+ ti->num_secure_erase_bios = 0;
+ ti->num_write_same_bios = 0;
+ ti->num_write_zeroes_bios = 0;
+ return 0;
+bad:
+ ebs_dtr(ti);
+ return r;
+}
+
+static void ebs_dtr(struct dm_target *ti)
+{
+ struct ebs_c *ec = ti->private;
+
+ if (ec->wq)
+ destroy_workqueue(ec->wq);
+ if (ec->bufio)
+ dm_bufio_client_destroy(ec->bufio);
+ if (ec->dev)
+ dm_put_device(ti, ec->dev);
+ kfree(ec);
+}
+
+static int ebs_map(struct dm_target *ti, struct bio *bio)
+{
+ struct ebs_c *ec = ti->private;
+
+ bio_set_dev(bio, ec->dev->bdev);
+ bio->bi_iter.bi_sector = ec->start + dm_target_offset(ti, bio->bi_iter.bi_sector);
+
+ if (unlikely(bio->bi_opf & REQ_OP_FLUSH))
+ return DM_MAPIO_REMAPPED;
+
+ /*
+ * Only queue for bufio processing in case of partial or overlapping buffers
+ * -or-
+ * emulation with ebs == ubs aiming for tests of dm-bufio overhead.
+ */
+ if (likely(__block_mod(bio->bi_iter.bi_sector, ec->ubs) ||
+ __block_mod(bio_end_sector(bio), ec->ubs) ||
+ ec->ebs == ec->ubs)) {
+ spin_lock_irq(&ec->lock);
+ bio_list_add(&ec->bios_in, bio);
+ spin_unlock_irq(&ec->lock);
+
+ queue_work(ec->wq, &ec->ws);
+
+ return DM_MAPIO_SUBMITTED;
+ }
+
+ /* Forget any buffer content relative to this direct backing device I/O. */
+ __ebs_forget_bio(ec, bio);
+
+ return DM_MAPIO_REMAPPED;
+}
+
+static void ebs_status(struct dm_target *ti, status_type_t type,
+ unsigned status_flags, char *result, unsigned maxlen)
+{
+ struct ebs_c *ec = ti->private;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ *result = '\0';
+ break;
+ case STATUSTYPE_TABLE:
+ snprintf(result, maxlen, ec->ubs_set ? "%s %llu %u %u" : "%s %llu %u",
+ ec->dev->name, (unsigned long long) ec->start, ec->ebs, ec->ubs);
+ break;
+ }
+}
+
+static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
+{
+ struct ebs_c *ec = ti->private;
+ struct dm_dev *dev = ec->dev;
+
+ /*
+ * Only pass ioctls through if the device sizes match exactly.
+ */
+ *bdev = dev->bdev;
+ return !!(ec->start || ti->len != i_size_read(dev->bdev->bd_inode) >> SECTOR_SHIFT);
+}
+
+static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+ struct ebs_c *ec = ti->private;
+
+ limits->logical_block_size = to_bytes(ec->ebs);
+ limits->physical_block_size = to_bytes(ec->ubs);
+ limits->alignment_offset = limits->physical_block_size;
+ blk_limits_io_min(limits, limits->logical_block_size);
+}
+
+static int ebs_iterate_devices(struct dm_target *ti,
+ iterate_devices_callout_fn fn, void *data)
+{
+ struct ebs_c *ec = ti->private;
+
+ return fn(ti, ec->dev, ec->start, ti->len, data);
+}
+
+static struct target_type ebs_target = {
+ .name = "ebs",
+ .version = {1, 0, 0},
+ .features = DM_TARGET_PASSES_INTEGRITY,
+ .module = THIS_MODULE,
+ .ctr = ebs_ctr,
+ .dtr = ebs_dtr,
+ .map = ebs_map,
+ .status = ebs_status,
+ .io_hints = ebs_io_hints,
+ .prepare_ioctl = ebs_prepare_ioctl,
+ .iterate_devices = ebs_iterate_devices,
+};
+
+int __init dm_ebs_init(void)
+{
+ int r = dm_register_target(&ebs_target);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+
+ return r;
+}
+
+void dm_ebs_exit(void)
+{
+ dm_unregister_target(&ebs_target);
+}
+
+module_init(dm_ebs_init);
+module_exit(dm_ebs_exit);
+
+MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@xxxxxxxxxx>");
+MODULE_DESCRIPTION(DM_NAME " emulated block size target");
+MODULE_LICENSE("GPL");
--
2.24.1
--
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