[dm-devel] [PATCH v3] dm ebs: new block size emulating target
Heinz Mauelshagen
heinzm at redhat.com
Fri Feb 21 15:20:04 UTC 2020
Bryan,
thanks for the review and testing.
See remarks below.
Heinz
On 2/21/20 4:08 PM, Bryan Gurney wrote:
> On Fri, Feb 21, 2020 at 9:26 AM Heinz Mauelshagen <heinzm at redhat.com> wrote:
>> Hi Damien,
>>
>> thanks for your review, much appreciated.
>>
>> Please find my statements inline with yours below, working in
>> uncontroversial ones now...
>>
>> Heinz
>>
>>
>> On 2/21/20 10:44 AM, Damien Le Moal wrote:
>>> 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 ?
>> dm-ebs is mainly providing software 512e, that's what the sentence
>> "It's main purpose is to emulate 512 byte sectors on 4K native disks
>> (i.e. 512e)
>> aimed to state.
>>
>> Would changing to '(i.e. software 512e)' help understanding?
>>
> I think it might be better phrased like this (which also fixes an
> "it's" versus "its" mixup):
>
> This new target is similar to the linear target, except that it emulates
> a smaller logical block size on devices with larger ones. Its main
> purpose is to provide emulation of 512 byte sectors on devices
> that do not provide this emulation (i.e. 4K native disks).
Better, taken apart from the 'new' upfront target.
Damien, what do you think?
>
>>>> 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.
>> See above...
>>
> Agreed here; in this case, it may be enough to simply remove the "(i.e
> 512e)" part.
Gone with your initial documentation change proposal I took.
>
> Other than that, I've done some initial testing with the v3 patch, and
> I like what I see so far.
Nice, looking forward to any other of your findings...
>
>
> Thanks,
>
> Bryan
>
>>>> +
>>>> +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 ?
>>
>> This is flexibly offering dm-bufio features. dm-ebs can be configured to
>> use larger dm-bufio buffer sizes if that's requested for e.g. testing,
>> though its
>> main use case is software 512e on 4K native disks.
>>
>>
>>> 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.
>>
>> You think Documentation/admin-guide/device-mapper/dm-ebs.rst,
>> lines 9+11 don't provide enough information in this regard?
>>
>> Maybe the change to '(i.e. software 512e)' as mentioned above
>> in combination with that documentation addresses your point?
>>
>>>> +
>>>> +
>>>> +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
>>
>> I'd prefer ebs and ubs vs. those. What about e_bs and u_bs?
>>
>> Besides, we don't use '*blocksz' in dm and rarely the long 'blocksize'
>> var name.
>>
>>
>>> And add comments to describe the struct fields.
>> Ok.
>>
>>>> + 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 ?
>> Does it make sense vs. relying on compiler optimizations.
>>>> +
>>>> +static sector_t __block_mod(sector_t sector, unsigned int bs)
>>>> +{
>>>> + return sector & (bs - 1);
>>>> +}
>>> inline for this one too ?
>> See above question.
>>>> +
>>>> +/* 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.
>> Ok.
>>>> +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...
>> Yep.
>>>> + 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("
>> Ok.
>>
>>>> + 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 ?
>> The check's just about being cautious here.
>>
>>>> + 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.
>> That's along a change point I forget because I allow this for flexibility
>> Using DMINFO now...
>>
>>>> +
>>>> + 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");
>>>>
>> --
>> dm-devel mailing list
>> dm-devel at redhat.com
>> https://www.redhat.com/mailman/listinfo/dm-devel
>
> --
> dm-devel mailing list
> dm-devel at redhat.com
> https://www.redhat.com/mailman/listinfo/dm-devel
--
===============================================================
Heinz Mauelshagen +49 2626 141200
Distinguished Engineer FAX +49 2626 924446
Red Hat GmbH
Am Sonnenhang 11
56242 Marienrachdorf
Germany heinzm at redhat.com
===============================================================
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