474 lines
12 KiB
C
474 lines
12 KiB
C
/*
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* Copyright (C) 2020 Red Hat GmbH
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*
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* This file is released under the GPL.
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*
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* Device-mapper target to emulate smaller logical block
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* size on backing devices exposing (natively) larger ones.
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*
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* E.g. 512 byte sector emulation on 4K native disks.
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*/
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#include "dm.h"
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#include <linux/module.h>
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#include <linux/workqueue.h>
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#include <linux/dm-bufio.h>
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#define DM_MSG_PREFIX "ebs"
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static void ebs_dtr(struct dm_target *ti);
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/* Emulated block size context. */
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struct ebs_c {
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struct dm_dev *dev; /* Underlying device to emulate block size on. */
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struct dm_bufio_client *bufio; /* Use dm-bufio for read and read-modify-write processing. */
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struct workqueue_struct *wq; /* Workqueue for ^ processing of bios. */
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struct work_struct ws; /* Work item used for ^. */
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struct bio_list bios_in; /* Worker bios input list. */
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spinlock_t lock; /* Guard bios input list above. */
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sector_t start; /* <start> table line argument, see ebs_ctr below. */
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unsigned int e_bs; /* Emulated block size in sectors exposed to upper layer. */
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unsigned int u_bs; /* Underlying block size in sectors retrieved from/set on lower layer device. */
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unsigned char block_shift; /* bitshift sectors -> blocks used in dm-bufio API. */
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bool u_bs_set:1; /* Flag to indicate underlying block size is set on table line. */
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};
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static inline sector_t __sector_to_block(struct ebs_c *ec, sector_t sector)
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{
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return sector >> ec->block_shift;
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}
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static inline sector_t __block_mod(sector_t sector, unsigned int bs)
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{
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return sector & (bs - 1);
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}
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/* Return number of blocks for a bio, accounting for misalignment of start and end sectors. */
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static inline unsigned int __nr_blocks(struct ebs_c *ec, struct bio *bio)
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{
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sector_t end_sector = __block_mod(bio->bi_iter.bi_sector, ec->u_bs) + bio_sectors(bio);
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return __sector_to_block(ec, end_sector) + (__block_mod(end_sector, ec->u_bs) ? 1 : 0);
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}
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static inline bool __ebs_check_bs(unsigned int bs)
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{
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return bs && is_power_of_2(bs);
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}
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/*
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* READ/WRITE:
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*
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* copy blocks between bufio blocks and bio vector's (partial/overlapping) pages.
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*/
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static int __ebs_rw_bvec(struct ebs_c *ec, int rw, struct bio_vec *bv, struct bvec_iter *iter)
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{
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int r = 0;
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unsigned char *ba, *pa;
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unsigned int cur_len;
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unsigned int bv_len = bv->bv_len;
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unsigned int buf_off = to_bytes(__block_mod(iter->bi_sector, ec->u_bs));
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sector_t block = __sector_to_block(ec, iter->bi_sector);
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struct dm_buffer *b;
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if (unlikely(!bv->bv_page || !bv_len))
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return -EIO;
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pa = bvec_virt(bv);
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/* Handle overlapping page <-> blocks */
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while (bv_len) {
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cur_len = min(dm_bufio_get_block_size(ec->bufio) - buf_off, bv_len);
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/* Avoid reading for writes in case bio vector's page overwrites block completely. */
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if (rw == READ || buf_off || bv_len < dm_bufio_get_block_size(ec->bufio))
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ba = dm_bufio_read(ec->bufio, block, &b);
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else
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ba = dm_bufio_new(ec->bufio, block, &b);
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if (IS_ERR(ba)) {
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/*
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* Carry on with next buffer, if any, to issue all possible
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* data but return error.
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*/
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r = PTR_ERR(ba);
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} else {
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/* Copy data to/from bio to buffer if read/new was successful above. */
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ba += buf_off;
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if (rw == READ) {
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memcpy(pa, ba, cur_len);
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flush_dcache_page(bv->bv_page);
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} else {
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flush_dcache_page(bv->bv_page);
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memcpy(ba, pa, cur_len);
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dm_bufio_mark_partial_buffer_dirty(b, buf_off, buf_off + cur_len);
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}
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dm_bufio_release(b);
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}
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pa += cur_len;
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bv_len -= cur_len;
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buf_off = 0;
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block++;
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}
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return r;
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}
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/* READ/WRITE: iterate bio vector's copying between (partial) pages and bufio blocks. */
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static int __ebs_rw_bio(struct ebs_c *ec, int rw, struct bio *bio)
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{
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int r = 0, rr;
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struct bio_vec bv;
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struct bvec_iter iter;
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bio_for_each_bvec(bv, bio, iter) {
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rr = __ebs_rw_bvec(ec, rw, &bv, &iter);
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if (rr)
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r = rr;
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}
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return r;
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}
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/*
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* Discard bio's blocks, i.e. pass discards down.
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*
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* Avoid discarding partial blocks at beginning and end;
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* return 0 in case no blocks can be discarded as a result.
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*/
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static int __ebs_discard_bio(struct ebs_c *ec, struct bio *bio)
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{
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sector_t block, blocks, sector = bio->bi_iter.bi_sector;
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block = __sector_to_block(ec, sector);
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blocks = __nr_blocks(ec, bio);
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/*
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* Partial first underlying block (__nr_blocks() may have
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* resulted in one block).
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*/
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if (__block_mod(sector, ec->u_bs)) {
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block++;
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blocks--;
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}
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/* Partial last underlying block if any. */
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if (blocks && __block_mod(bio_end_sector(bio), ec->u_bs))
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blocks--;
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return blocks ? dm_bufio_issue_discard(ec->bufio, block, blocks) : 0;
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}
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/* Release blocks them from the bufio cache. */
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static void __ebs_forget_bio(struct ebs_c *ec, struct bio *bio)
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{
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sector_t blocks, sector = bio->bi_iter.bi_sector;
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blocks = __nr_blocks(ec, bio);
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dm_bufio_forget_buffers(ec->bufio, __sector_to_block(ec, sector), blocks);
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}
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/* Worker function to process incoming bios. */
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static void __ebs_process_bios(struct work_struct *ws)
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{
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int r;
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bool write = false;
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sector_t block1, block2;
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struct ebs_c *ec = container_of(ws, struct ebs_c, ws);
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struct bio *bio;
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struct bio_list bios;
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bio_list_init(&bios);
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spin_lock_irq(&ec->lock);
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bios = ec->bios_in;
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bio_list_init(&ec->bios_in);
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spin_unlock_irq(&ec->lock);
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/* Prefetch all read and any mis-aligned write buffers */
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bio_list_for_each(bio, &bios) {
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block1 = __sector_to_block(ec, bio->bi_iter.bi_sector);
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if (bio_op(bio) == REQ_OP_READ)
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dm_bufio_prefetch(ec->bufio, block1, __nr_blocks(ec, bio));
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else if (bio_op(bio) == REQ_OP_WRITE && !(bio->bi_opf & REQ_PREFLUSH)) {
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block2 = __sector_to_block(ec, bio_end_sector(bio));
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if (__block_mod(bio->bi_iter.bi_sector, ec->u_bs))
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dm_bufio_prefetch(ec->bufio, block1, 1);
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if (__block_mod(bio_end_sector(bio), ec->u_bs) && block2 != block1)
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dm_bufio_prefetch(ec->bufio, block2, 1);
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}
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}
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bio_list_for_each(bio, &bios) {
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r = -EIO;
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if (bio_op(bio) == REQ_OP_READ)
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r = __ebs_rw_bio(ec, READ, bio);
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else if (bio_op(bio) == REQ_OP_WRITE) {
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write = true;
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r = __ebs_rw_bio(ec, WRITE, bio);
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} else if (bio_op(bio) == REQ_OP_DISCARD) {
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__ebs_forget_bio(ec, bio);
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r = __ebs_discard_bio(ec, bio);
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}
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if (r < 0)
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bio->bi_status = errno_to_blk_status(r);
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}
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/*
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* We write dirty buffers after processing I/O on them
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* but before we endio thus addressing REQ_FUA/REQ_SYNC.
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*/
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r = write ? dm_bufio_write_dirty_buffers(ec->bufio) : 0;
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while ((bio = bio_list_pop(&bios))) {
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/* Any other request is endioed. */
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if (unlikely(r && bio_op(bio) == REQ_OP_WRITE))
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bio_io_error(bio);
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else
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bio_endio(bio);
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}
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}
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/*
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* Construct an emulated block size mapping: <dev_path> <offset> <ebs> [<ubs>]
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*
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* <dev_path>: path of the underlying device
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* <offset>: offset in 512 bytes sectors into <dev_path>
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* <ebs>: emulated block size in units of 512 bytes exposed to the upper layer
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* [<ubs>]: underlying block size in units of 512 bytes imposed on the lower layer;
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* optional, if not supplied, retrieve logical block size from underlying device
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*/
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static int ebs_ctr(struct dm_target *ti, unsigned int argc, char **argv)
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{
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int r;
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unsigned short tmp1;
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unsigned long long tmp;
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char dummy;
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struct ebs_c *ec;
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if (argc < 3 || argc > 4) {
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ti->error = "Invalid argument count";
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return -EINVAL;
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}
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ec = ti->private = kzalloc(sizeof(*ec), GFP_KERNEL);
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if (!ec) {
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ti->error = "Cannot allocate ebs context";
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return -ENOMEM;
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}
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r = -EINVAL;
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if (sscanf(argv[1], "%llu%c", &tmp, &dummy) != 1 ||
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tmp != (sector_t)tmp ||
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(sector_t)tmp >= ti->len) {
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ti->error = "Invalid device offset sector";
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goto bad;
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}
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ec->start = tmp;
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if (sscanf(argv[2], "%hu%c", &tmp1, &dummy) != 1 ||
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!__ebs_check_bs(tmp1) ||
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to_bytes(tmp1) > PAGE_SIZE) {
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ti->error = "Invalid emulated block size";
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goto bad;
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}
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ec->e_bs = tmp1;
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if (argc > 3) {
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if (sscanf(argv[3], "%hu%c", &tmp1, &dummy) != 1 || !__ebs_check_bs(tmp1)) {
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ti->error = "Invalid underlying block size";
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goto bad;
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}
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ec->u_bs = tmp1;
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ec->u_bs_set = true;
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} else
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ec->u_bs_set = false;
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r = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table), &ec->dev);
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if (r) {
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ti->error = "Device lookup failed";
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ec->dev = NULL;
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goto bad;
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}
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r = -EINVAL;
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if (!ec->u_bs_set) {
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ec->u_bs = to_sector(bdev_logical_block_size(ec->dev->bdev));
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if (!__ebs_check_bs(ec->u_bs)) {
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ti->error = "Invalid retrieved underlying block size";
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goto bad;
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}
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}
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if (!ec->u_bs_set && ec->e_bs == ec->u_bs)
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DMINFO("Emulation superfluous: emulated equal to underlying block size");
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if (__block_mod(ec->start, ec->u_bs)) {
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ti->error = "Device offset must be multiple of underlying block size";
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goto bad;
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}
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ec->bufio = dm_bufio_client_create(ec->dev->bdev, to_bytes(ec->u_bs), 1, 0, NULL, NULL);
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if (IS_ERR(ec->bufio)) {
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ti->error = "Cannot create dm bufio client";
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r = PTR_ERR(ec->bufio);
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ec->bufio = NULL;
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goto bad;
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}
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ec->wq = alloc_ordered_workqueue("dm-" DM_MSG_PREFIX, WQ_MEM_RECLAIM);
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if (!ec->wq) {
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ti->error = "Cannot create dm-" DM_MSG_PREFIX " workqueue";
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r = -ENOMEM;
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goto bad;
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}
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ec->block_shift = __ffs(ec->u_bs);
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INIT_WORK(&ec->ws, &__ebs_process_bios);
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bio_list_init(&ec->bios_in);
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spin_lock_init(&ec->lock);
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ti->num_flush_bios = 1;
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ti->num_discard_bios = 1;
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ti->num_secure_erase_bios = 0;
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ti->num_write_zeroes_bios = 0;
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return 0;
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bad:
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ebs_dtr(ti);
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return r;
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}
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static void ebs_dtr(struct dm_target *ti)
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{
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struct ebs_c *ec = ti->private;
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if (ec->wq)
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destroy_workqueue(ec->wq);
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if (ec->bufio)
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dm_bufio_client_destroy(ec->bufio);
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if (ec->dev)
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dm_put_device(ti, ec->dev);
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kfree(ec);
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}
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static int ebs_map(struct dm_target *ti, struct bio *bio)
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{
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struct ebs_c *ec = ti->private;
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bio_set_dev(bio, ec->dev->bdev);
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bio->bi_iter.bi_sector = ec->start + dm_target_offset(ti, bio->bi_iter.bi_sector);
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if (unlikely(bio_op(bio) == REQ_OP_FLUSH))
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return DM_MAPIO_REMAPPED;
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/*
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* Only queue for bufio processing in case of partial or overlapping buffers
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* -or-
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* emulation with ebs == ubs aiming for tests of dm-bufio overhead.
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*/
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if (likely(__block_mod(bio->bi_iter.bi_sector, ec->u_bs) ||
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__block_mod(bio_end_sector(bio), ec->u_bs) ||
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ec->e_bs == ec->u_bs)) {
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spin_lock_irq(&ec->lock);
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bio_list_add(&ec->bios_in, bio);
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spin_unlock_irq(&ec->lock);
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queue_work(ec->wq, &ec->ws);
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return DM_MAPIO_SUBMITTED;
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}
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/* Forget any buffer content relative to this direct backing device I/O. */
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__ebs_forget_bio(ec, bio);
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return DM_MAPIO_REMAPPED;
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}
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static void ebs_status(struct dm_target *ti, status_type_t type,
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unsigned status_flags, char *result, unsigned maxlen)
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{
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struct ebs_c *ec = ti->private;
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switch (type) {
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case STATUSTYPE_INFO:
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*result = '\0';
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break;
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case STATUSTYPE_TABLE:
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snprintf(result, maxlen, ec->u_bs_set ? "%s %llu %u %u" : "%s %llu %u",
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ec->dev->name, (unsigned long long) ec->start, ec->e_bs, ec->u_bs);
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break;
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case STATUSTYPE_IMA:
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*result = '\0';
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break;
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}
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}
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static int ebs_prepare_ioctl(struct dm_target *ti, struct block_device **bdev)
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{
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struct ebs_c *ec = ti->private;
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struct dm_dev *dev = ec->dev;
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/*
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* Only pass ioctls through if the device sizes match exactly.
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*/
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*bdev = dev->bdev;
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return !!(ec->start || ti->len != bdev_nr_sectors(dev->bdev));
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}
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static void ebs_io_hints(struct dm_target *ti, struct queue_limits *limits)
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{
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struct ebs_c *ec = ti->private;
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limits->logical_block_size = to_bytes(ec->e_bs);
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limits->physical_block_size = to_bytes(ec->u_bs);
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limits->alignment_offset = limits->physical_block_size;
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blk_limits_io_min(limits, limits->logical_block_size);
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}
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static int ebs_iterate_devices(struct dm_target *ti,
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iterate_devices_callout_fn fn, void *data)
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{
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struct ebs_c *ec = ti->private;
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return fn(ti, ec->dev, ec->start, ti->len, data);
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}
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static struct target_type ebs_target = {
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.name = "ebs",
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.version = {1, 0, 1},
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.features = DM_TARGET_PASSES_INTEGRITY,
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.module = THIS_MODULE,
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.ctr = ebs_ctr,
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.dtr = ebs_dtr,
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.map = ebs_map,
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.status = ebs_status,
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.io_hints = ebs_io_hints,
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.prepare_ioctl = ebs_prepare_ioctl,
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.iterate_devices = ebs_iterate_devices,
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};
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static int __init dm_ebs_init(void)
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{
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int r = dm_register_target(&ebs_target);
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if (r < 0)
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DMERR("register failed %d", r);
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return r;
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}
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static void dm_ebs_exit(void)
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{
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dm_unregister_target(&ebs_target);
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}
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module_init(dm_ebs_init);
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module_exit(dm_ebs_exit);
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MODULE_AUTHOR("Heinz Mauelshagen <dm-devel@redhat.com>");
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MODULE_DESCRIPTION(DM_NAME " emulated block size target");
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MODULE_LICENSE("GPL");
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