[dm-devel] [PATCH v3] dm ebs: new block size emulating target
Damien Le Moal
Damien.LeMoal at wdc.com
Fri Feb 21 09:44:22 UTC 2020
On 2020/02/20 7:12, heinzm at redhat.com wrote:
> From: Heinz Mauelshagen <heinzm at redhat.com>
>
> 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).
512e drives have a 512B LBA, so no emulation is needed (the drive does that
itself). Did you mean to say 4Kn here ? Or is the intent to bypass the
drive level 512B emulation and do all 4K aligned read-modify-write accesses
on the host ?
>
> See Documentation/admin-guide/device-mapper/dm-ebs.rst for details.
>
> Changes versus version 2 sent on 2/13/2020:
> - fix __nr_blocks() to return the correct number of blocks
> - fix __ebs_forget_bio() to process the last block of a bio
> - fix __ebs_process_bios() to avoid prefetching the same block twice
> - use op_is_flush() in the map function
> - comments
>
> Reviewed-by: John Dorminy <jdorminy at redhat.com>
> Signed-off-by: Heinz Mauelshagen <heinzm at redhat.com>
> ---
> .../admin-guide/device-mapper/dm-ebs.rst | 49 ++
> drivers/md/Kconfig | 8 +
> drivers/md/Makefile | 2 +
> drivers/md/dm-ebs-target.c | 429 ++++++++++++++++++
> 4 files changed, 488 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).
Same comment as above. Clarifying this would help users.
> +
> +Supported emulated logical block sizes 512, 1024, 2048 and 4096.
> +
> +Underlying block size can be set to > 4K to test buffering larger units.
If I understand this correctly, your target can also emulate physical
sector sizes larger than 4K ? Is this correct ?
All this description should I think clarify the combinations of
logical/physical sector size that the target can take and change into some
other combination.
> +
> +
> +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..a241af82543a
> --- /dev/null
> +++ b/drivers/md/dm-ebs-target.c
> @@ -0,0 +1,429 @@
> +/*
> + * 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;
These two should have better name to help clarifying the code.
May be:
ebs -> elblocksz
ubs -> epblocksz
And add comments to describe the struct fields.
> + 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 inline sector_t ?
> +
> +static sector_t __block_mod(sector_t sector, unsigned int bs)
> +{
> + return sector & (bs - 1);
> +}
inline for this one too ?
> +
> +/* Return number of blocks for a bio accounting for misalignement of start and end sectors. */
> +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. */
May be use the regular comment block for functions here:
/*
* READ/WRITE...
*/
Same for other functions below.
> +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 to I/O all possible data 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 blocks, sector = bio->bi_iter.bi_sector;;
> +
> + blocks = __nr_blocks(ec, bio);
> + for (; blocks--; 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;
> + sector_t block1, block2;
> + 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) {
> + block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
> + if (bio_op(bio) == REQ_OP_READ)
> + dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
> + else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
> + block2 = __sector_to_block(ec, bio_end_sector(bio));
> + if (__block_mod(bio->bi_iter.bi_sector, ec->ubs))
> + dm_bufio_prefetch(ec->bufio, block1, 1);
> + if (__block_mod(bio_end_sector(bio), ec->ubs) && block2 != block1)
> + dm_bufio_prefetch(ec->bufio, block2, 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: (optionally) 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. */
Then please fix it...
> + 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) {
please indent to the "if (", not "sscanf("
> + 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";
The message is confusing here. The device LBA size is certainly fine, but
the parameters passed cannot accomodate it right ? So stricktly speaking,
it is not the backend device LBA size that is invalid. No ?
> + goto bad;
> + }
> + }
> +
> + if (!ec->ubs_set && ec->ebs == ec->ubs)
> + DMERR("Emulation superfluous: emulated equal to underlying block size");
This is an error message but you do nothing about it. May be change this
into a info level output since that is not a real problem.
> +
> + 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(op_is_flush(bio->bi_opf)))
> + 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 at redhat.com>");
> +MODULE_DESCRIPTION(DM_NAME " emulated block size target");
> +MODULE_LICENSE("GPL");
>
--
Damien Le Moal
Western Digital Research
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