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    SubjectRe: [PATCH][RFC] fast file mapping for loop
    Here's the latest version of dm-loop, for comparison.

    To try it out,
    ln -s dmsetup dmlosetup
    and supply similar basic parameters to losetup.
    (using dmsetup version 1.02.11 or higher)

    Alasdair

    From: Bryn Reeves <breeves@redhat.com>

    This implements a loopback target for device mapper allowing a regular
    file to be treated as a block device.

    Signed-off-by: Bryn Reeves <breeves@redhat.com>
    Signed-off-by: Alasdair G Kergon <agk@redhat.com>

    ---
    drivers/md/Kconfig | 9
    drivers/md/Makefile | 1
    drivers/md/dm-loop.c | 1036 +++++++++++++++++++++++++++++++++++++++++++++++++++
    3 files changed, 1046 insertions(+)

    Index: linux-2.6.24-rc6/drivers/md/Kconfig
    ===================================================================
    --- linux-2.6.24-rc6.orig/drivers/md/Kconfig 2008-01-07 18:32:05.000000000 +0000
    +++ linux-2.6.24-rc6/drivers/md/Kconfig 2008-01-07 18:33:12.000000000 +0000
    @@ -229,6 +229,15 @@ config DM_CRYPT

    If unsure, say N.

    +config DM_LOOP
    + tristate "Loop target (EXPERIMENTAL)"
    + depends on BLK_DEV_DM && EXPERIMENTAL
    + ---help---
    + This device-mapper target allows you to treat a regular file as
    + a block device.
    +
    + If unsure, say N.
    +
    config DM_SNAPSHOT
    tristate "Snapshot target (EXPERIMENTAL)"
    depends on BLK_DEV_DM && EXPERIMENTAL
    Index: linux-2.6.24-rc6/drivers/md/Makefile
    ===================================================================
    --- linux-2.6.24-rc6.orig/drivers/md/Makefile 2008-01-07 18:32:05.000000000 +0000
    +++ linux-2.6.24-rc6/drivers/md/Makefile 2008-01-07 18:33:12.000000000 +0000
    @@ -34,6 +34,7 @@ obj-$(CONFIG_BLK_DEV_MD) += md-mod.o
    obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o
    obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
    obj-$(CONFIG_DM_DELAY) += dm-delay.o
    +obj-$(CONFIG_DM_LOOP) += dm-loop.o
    obj-$(CONFIG_DM_MULTIPATH) += dm-multipath.o dm-round-robin.o
    obj-$(CONFIG_DM_MULTIPATH_EMC) += dm-emc.o
    obj-$(CONFIG_DM_MULTIPATH_HP) += dm-hp-sw.o
    Index: linux-2.6.24-rc6/drivers/md/dm-loop.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-2.6.24-rc6/drivers/md/dm-loop.c 2008-01-07 18:33:12.000000000 +0000
    @@ -0,0 +1,1036 @@
    +/*
    + * Copyright (C) 2006-2008 Red Hat, Inc. All rights reserved.
    + *
    + * This file is part of device-mapper.
    + *
    + * Extent mapping implementation heavily influenced by mm/swapfile.c
    + * Bryn Reeves <breeves@redhat.com>
    + *
    + * File mapping and block lookup algorithms support by
    + * Heinz Mauelshagen <hjm@redhat.com>.
    + *
    + * This file is released under the GPL.
    + */
    +
    +#include <linux/kernel.h>
    +#include <linux/slab.h>
    +#include <linux/fs.h>
    +#include <linux/module.h>
    +#include <linux/vmalloc.h>
    +#include <linux/syscalls.h>
    +#include <linux/workqueue.h>
    +#include <linux/file.h>
    +#include <linux/bio.h>
    +
    +#include "dm.h"
    +#include "dm-bio-list.h"
    +
    +#define DM_LOOP_DAEMON "kloopd"
    +#define DM_MSG_PREFIX "loop"
    +
    +enum flags { DM_LOOP_BMAP, DM_LOOP_FSIO };
    +
    +/*--------------------------------------------------------------------
    + * Loop context
    + *--------------------------------------------------------------------*/
    +
    +struct loop_c {
    + unsigned long flags;
    +
    + /* Backing store */
    +
    + struct file *filp;
    + char *path;
    + loff_t offset;
    + struct block_device *bdev;
    + unsigned blkbits; /* file system block size shift bits */
    +
    + loff_t size; /* size of entire file in bytes */
    + loff_t blocks; /* blocks allocated to loop file */
    + sector_t mapped_sectors; /* size of mapped area in sectors */
    +
    + int (*map_fn)(struct dm_target *, struct bio *);
    + void *map_data;
    +};
    +
    +/*
    + * Block map extent
    + */
    +struct dm_loop_extent {
    + sector_t start; /* start sector in mapped device */
    + sector_t to; /* start sector on target device */
    + sector_t len; /* length in sectors */
    +};
    +
    +/*
    + * Temporary extent list
    + */
    +struct extent_list {
    + struct dm_loop_extent *extent;
    + struct list_head list;
    +};
    +
    +static struct kmem_cache *dm_loop_extent_cache;
    +
    +/*
    + * Block map private context
    + */
    +struct block_map_c {
    + int nr_extents; /* number of extents in map */
    + struct dm_loop_extent **map; /* linear map of extent pointers */
    + struct dm_loop_extent **mru; /* pointer to mru entry */
    + spinlock_t mru_lock; /* protects mru */
    +};
    +
    +/*
    + * File map private context
    + */
    +struct file_map_c {
    + spinlock_t lock; /* protects in */
    + struct bio_list in; /* new bios for processing */
    + struct bio_list work; /* bios queued for processing */
    + struct workqueue_struct *wq; /* workqueue */
    + struct work_struct ws; /* loop work */
    + struct loop_c *loop; /* for filp & offset */
    +};
    +
    +/*--------------------------------------------------------------------
    + * Generic helpers
    + *--------------------------------------------------------------------*/
    +
    +static sector_t blk2sect(struct loop_c *lc, blkcnt_t block)
    +{
    + return block << (lc->blkbits - SECTOR_SHIFT);
    +}
    +
    +static blkcnt_t sec2blk(struct loop_c *lc, sector_t sector)
    +{
    + return sector >> (lc->blkbits - SECTOR_SHIFT);
    +}
    +
    +/*--------------------------------------------------------------------
    + * File I/O helpers
    + *--------------------------------------------------------------------*/
    +
    +/*
    + * transfer data to/from file using the read/write file_operations.
    + */
    +static int fs_io(int rw, struct file *filp, loff_t *pos, struct bio_vec *bv)
    +{
    + ssize_t r;
    + void __user *ptr = (void __user __force *) kmap(bv->bv_page) + bv->bv_offset;
    + mm_segment_t old_fs = get_fs();
    +
    + set_fs(get_ds());
    + r = (rw == READ) ? filp->f_op->read(filp, ptr, bv->bv_len, pos) :
    + filp->f_op->write(filp, ptr, bv->bv_len, pos);
    + set_fs(old_fs);
    + kunmap(bv->bv_page);
    +
    + return (r == bv->bv_len) ? 0 : -EIO;
    +}
    +
    +/*
    + * Handle I/O for one bio
    + */
    +static void do_one_bio(struct file_map_c *fc, struct bio *bio)
    +{
    + int r = 0, rw = bio_data_dir(bio);
    + loff_t start = (bio->bi_sector << 9) + fc->loop->offset, pos = start;
    + struct bio_vec *bv, *bv_end = bio->bi_io_vec + bio->bi_vcnt;
    +
    + for (bv = bio->bi_io_vec; bv < bv_end; bv++) {
    + r = fs_io(rw, fc->loop->filp, &pos, bv);
    + if (r) {
    + DMERR("%s error %d", rw ? "write" : "read", r);
    + break;
    + }
    + }
    +
    + bio_endio(bio, r);
    +}
    +
    +/*
    + * Worker thread for a 'file' type loop device
    + */
    +static void do_loop_work(struct work_struct *ws)
    +{
    + struct file_map_c *fc = container_of(ws, struct file_map_c, ws);
    + struct bio *bio;
    +
    + /* quickly grab all new bios queued and add them to the work list */
    + spin_lock_irq(&fc->lock);
    + bio_list_merge(&fc->work, &fc->in);
    + bio_list_init(&fc->in);
    + spin_unlock_irq(&fc->lock);
    +
    + /* work the list and do file I/O on all bios */
    + while ((bio = bio_list_pop(&fc->work)))
    + do_one_bio(fc, bio);
    +}
    +
    +/*
    + * Create work queue and initialize work
    + */
    +static int loop_work_init(struct loop_c *lc)
    +{
    + struct file_map_c *fc = lc->map_data;
    +
    + fc->wq = create_singlethread_workqueue(DM_LOOP_DAEMON);
    + if (!fc->wq)
    + return -ENOMEM;
    +
    + return 0;
    +}
    +
    +/*
    + * Destroy work queue
    + */
    +static void loop_work_exit(struct loop_c *lc)
    +{
    + struct file_map_c *fc = lc->map_data;
    +
    + if (fc->wq)
    + destroy_workqueue(fc->wq);
    +}
    +
    +/*
    + * DM_LOOP_FSIO map_fn. Mapping just queues bios to the file map
    + * context and lets the daemon deal with them.
    + */
    +static int loop_file_map(struct dm_target *ti, struct bio *bio)
    +{
    + int wake;
    + struct loop_c *lc = ti->private;
    + struct file_map_c *fc = lc->map_data;
    +
    + spin_lock_irq(&fc->lock);
    + wake = bio_list_empty(&fc->in);
    + bio_list_add(&fc->in, bio);
    + spin_unlock_irq(&fc->lock);
    +
    + /*
    + * Only call queue_work() if necessary to avoid
    + * superfluous preempt_{disable/enable}() overhead.
    + */
    + if (wake)
    + queue_work(fc->wq, &fc->ws);
    +
    + /* Handling bio - will submit later. */
    + return 0;
    +}
    +
    +/*
    + * Shutdown the workqueue and free a file mapping
    + */
    +static void destroy_file_map(struct loop_c *lc)
    +{
    + loop_work_exit(lc);
    + kfree(lc->map_data);
    +}
    +
    +/*
    + * Set up a file map context and workqueue
    + */
    +static int setup_file_map(struct loop_c *lc)
    +{
    + struct file_map_c *fc = kzalloc(sizeof(*fc), GFP_KERNEL);
    +
    + if (!fc)
    + return -ENOMEM;
    +
    + spin_lock_init(&fc->lock);
    + bio_list_init(&fc->in);
    + bio_list_init(&fc->work);
    + INIT_WORK(&fc->ws, do_loop_work);
    + fc->loop = lc;
    +
    + lc->map_data = fc;
    + lc->map_fn = loop_file_map;
    +
    + return loop_work_init(lc);
    +}
    +
    +/*--------------------------------------------------------------------
    + * Block I/O helpers
    + *--------------------------------------------------------------------*/
    +
    +static int contains_sector(struct dm_loop_extent *e, sector_t s)
    +{
    + if (likely(e))
    + return s < (e->start + (e->len)) && s >= e->start;
    +
    + return 0;
    +}
    +
    +/*
    + * Walk over a linked list of extent_list structures, freeing them as
    + * we go. Does not free el->extent.
    + */
    +static void destroy_extent_list(struct list_head *head)
    +{
    + struct list_head *curr, *n;
    + struct extent_list *el;
    +
    + if (list_empty(head))
    + return;
    +
    + list_for_each_safe(curr, n, head) {
    + el = list_entry(curr, struct extent_list, list);
    + list_del(curr);
    + kfree(el);
    + }
    +}
    +
    +/*
    + * Add a new extent to the tail of the list at *head with
    + * start/to/len parameters. Allocates from the extent cache.
    + */
    +static int list_add_extent(struct list_head *head, sector_t start,
    + sector_t to, sector_t len)
    +{
    + struct dm_loop_extent *extent;
    + struct extent_list *list;
    +
    + extent = kmem_cache_alloc(dm_loop_extent_cache, GFP_KERNEL);
    + if (!extent)
    + goto out;
    +
    + list = kmalloc(sizeof(*list), GFP_KERNEL);
    + if (!list)
    + goto out;
    +
    + extent->start = start;
    + extent->to = to;
    + extent->len = len;
    +
    + list->extent = extent;
    + list_add_tail(&list->list, head);
    +
    + return 0;
    +out:
    + if (extent)
    + kmem_cache_free(dm_loop_extent_cache, extent);
    + return -ENOMEM;
    +}
    +
    +/*
    + * Return an extent range (i.e. beginning and ending physical block numbers).
    + */
    +static int extent_range(struct inode *inode,
    + blkcnt_t logical_blk, blkcnt_t last_blk,
    + blkcnt_t *begin_blk, blkcnt_t *end_blk)
    +{
    + sector_t dist = 0, phys_blk, probe_blk = logical_blk;
    +
    + /* Find beginning physical block of extent starting at logical_blk. */
    + *begin_blk = phys_blk = bmap(inode, probe_blk);
    + if (!phys_blk)
    + return -ENXIO;
    +
    + for (; phys_blk == *begin_blk + dist; dist++) {
    + *end_blk = phys_blk;
    + if (++probe_blk > last_blk)
    + break;
    +
    + phys_blk = bmap(inode, probe_blk);
    + if (unlikely(!phys_blk))
    + return -ENXIO;
    + }
    +
    + return 0;
    +}
    +
    +/*
    + * Create a sequential list of extents from an inode and return
    + * it in *head. On success return the number of extents found or
    + * -ERRNO on failure.
    + */
    +static int loop_extents(struct loop_c *lc, struct inode *inode,
    + struct list_head *head)
    +{
    + sector_t start = 0;
    + int r, nr_extents = 0;
    + blkcnt_t nr_blks = 0, begin_blk = 0, end_blk = 0;
    + blkcnt_t after_last_blk = sec2blk(lc,
    + (lc->mapped_sectors + (lc->offset >> 9)));
    + blkcnt_t logical_blk = sec2blk(lc, (lc->offset >> 9));
    +
    + /* for each block in the mapped region */
    + while (logical_blk < after_last_blk) {
    + r = extent_range(inode, logical_blk, after_last_blk - 1,
    + &begin_blk, &end_blk);
    +
    + /* sparse file fallback */
    + if (unlikely(r)) {
    + DMWARN("%s has a hole; sparse file detected - "
    + "switching to filesystem I/O", lc->path);
    + clear_bit(DM_LOOP_BMAP, &lc->flags);
    + set_bit(DM_LOOP_FSIO, &lc->flags);
    + return r;
    + }
    +
    + nr_blks = 1 + end_blk - begin_blk;
    +
    + if (unlikely(!nr_blks))
    + continue;
    +
    + r = list_add_extent(head, start, blk2sect(lc, begin_blk),
    + blk2sect(lc, nr_blks));
    + if (unlikely(r))
    + return r;
    +
    + /* advance to next extent */
    + nr_extents++;
    + start += blk2sect(lc, nr_blks);
    + logical_blk += nr_blks;
    + }
    +
    + return nr_extents;
    +}
    +
    +/*
    + * Walk over the extents in a block_map_c, returning them to the cache and
    + * freeing bc->map and bc.
    + */
    +static void destroy_block_map(struct block_map_c *bc)
    +{
    + unsigned i;
    +
    + if (!bc)
    + return;
    +
    + for (i = 0; i < bc->nr_extents; i++)
    + kmem_cache_free(dm_loop_extent_cache, bc->map[i]);
    +
    + DMDEBUG("destroying block map of %d entries", i);
    +
    + vfree(bc->map);
    + kfree(bc);
    +}
    +
    +/*
    + * Find an extent in *bc using binary search. Returns a pointer into the
    + * extent map. Calculate index as (extent - bc->map).
    + */
    +static struct dm_loop_extent **extent_binary_lookup(struct block_map_c *bc,
    + struct dm_loop_extent **extent_mru, sector_t sector)
    +{
    + unsigned nr_extents = bc->nr_extents;
    + unsigned delta, dist, prev_dist = 0;
    + struct dm_loop_extent **eptr;
    +
    + /* Optimize lookup range based on MRU extent. */
    + dist = extent_mru - bc->map;
    + if ((*extent_mru)->start >= sector)
    + delta = dist = dist / 2;
    + else {
    + delta = (nr_extents - dist) / 2;
    + dist += delta;
    + }
    +
    + eptr = bc->map + dist;
    + while (*eptr && !contains_sector(*eptr, sector)) {
    + if (sector >= (*eptr)->start + (*eptr)->len) {
    + prev_dist = dist;
    + if (delta > 1)
    + delta /= 2;
    + dist += delta;
    + } else {
    + delta = (dist - prev_dist) / 2;
    + if (!delta)
    + delta = 1;
    + dist -= delta;
    + }
    + eptr = bc->map + dist;
    + }
    +
    + return eptr;
    +}
    +
    +/*
    + * Lookup an extent for a sector using the mru cache and binary search.
    + */
    +static struct dm_loop_extent *extent_lookup(struct block_map_c *bc, sector_t sector)
    +{
    + struct dm_loop_extent **eptr;
    +
    + spin_lock_irq(&bc->mru_lock);
    + eptr = bc->mru;
    + spin_unlock_irq(&bc->mru_lock);
    +
    + if (contains_sector(*eptr, sector))
    + return *eptr;
    +
    + eptr = extent_binary_lookup(bc, eptr, sector);
    + if (!eptr)
    + return NULL;
    +
    + spin_lock_irq(&bc->mru_lock);
    + bc->mru = eptr;
    + spin_unlock_irq(&bc->mru_lock);
    +
    + return *eptr;
    +}
    +
    +/*
    + * DM_LOOP_BMAP map_fn. Looks up the sector in the extent map and
    + * rewrites the bio device and bi_sector fields.
    + */
    +static int loop_block_map(struct dm_target *ti, struct bio *bio)
    +{
    + struct loop_c *lc = ti->private;
    + struct dm_loop_extent *extent = extent_lookup(lc->map_data, bio->bi_sector);
    +
    + if (likely(extent)) {
    + bio->bi_bdev = lc->bdev;
    + bio->bi_sector = extent->to + (bio->bi_sector - extent->start);
    + return 1; /* Done with bio -> submit */
    + }
    +
    + DMERR("no matching extent in map for sector %llu",
    + (unsigned long long) bio->bi_sector + ti->begin);
    + BUG();
    +
    + return -EIO;
    +}
    +
    +/*
    + * Turn an extent_list into a linear pointer map of nr_extents + 1 entries
    + * and set the final entry to NULL.
    + */
    +static struct dm_loop_extent **build_extent_map(struct list_head *head, int nr_extents,
    + unsigned long *flags)
    +{
    + unsigned map_size, cache_size;
    + struct dm_loop_extent **map, **curr;
    + struct list_head *pos;
    + struct extent_list *el;
    +
    + map_size = 1 + (sizeof(*map) * nr_extents);
    + cache_size = kmem_cache_size(dm_loop_extent_cache) * nr_extents;
    +
    + map = vmalloc(map_size);
    + curr = map;
    +
    + DMDEBUG("allocated extent map of %u %s for %d extents (%u %s)",
    + (map_size < 8192) ? map_size : map_size >> 10,
    + (map_size < 8192) ? "bytes" : "kilobytes", nr_extents,
    + (cache_size < 8192) ? cache_size : cache_size >> 10,
    + (cache_size < 8192) ? "bytes" : "kilobytes");
    +
    + list_for_each(pos, head) {
    + el = list_entry(pos, struct extent_list, list);
    + *(curr++) = el->extent;
    + }
    + *curr = NULL;
    +
    + return map;
    +}
    +
    +/*
    + * Set up a block map context and extent map
    + */
    +static int setup_block_map(struct loop_c *lc, struct inode *inode)
    +{
    + int r, nr_extents;
    + struct block_map_c *bc;
    + LIST_HEAD(head);
    +
    + if (!inode || !inode->i_sb || !inode->i_sb->s_bdev)
    + return -ENXIO;
    +
    + /* build a linked list of extents in linear order */
    + r = nr_extents = loop_extents(lc, inode, &head);
    + if (nr_extents < 1)
    + goto out;
    +
    + r = -ENOMEM;
    + bc = kzalloc(sizeof(*bc), GFP_KERNEL);
    + if (!bc)
    + goto out;
    +
    + /* create a linear map of pointers into the extent cache */
    + bc->map = build_extent_map(&head, nr_extents, &lc->flags);
    + destroy_extent_list(&head);
    +
    + if (IS_ERR(bc->map)) {
    + r = PTR_ERR(bc->map);
    + goto out;
    + }
    +
    + spin_lock_init(&bc->mru_lock);
    + bc->mru = bc->map;
    + bc->nr_extents = nr_extents;
    + lc->bdev = inode->i_sb->s_bdev;
    + lc->map_data = bc;
    + lc->map_fn = loop_block_map;
    +
    + return 0;
    +
    +out:
    + return r;
    +}
    +
    +/*--------------------------------------------------------------------
    + * Generic helpers
    + *--------------------------------------------------------------------*/
    +
    +/*
    + * Invalidate all unlocked loop file pages
    + */
    +static int loop_invalidate_file(struct file *filp)
    +{
    + int r;
    +
    + /* Same as generic_file_direct_IO() */
    + unmap_mapping_range(filp->f_mapping, 0, ~0UL, 0);
    +
    + r = filemap_write_and_wait(filp->f_mapping);
    + if (r)
    + return r;
    +
    + /*
    + * This will remove all pages except dirty ones.
    + * If there are dirty pages at this point, it means that the user
    + * is writing to the file and the coherency is lost anyway.
    + * If the user was writing to the file simultaneously, this
    + * returns non-zero, but we ignore that.
    + */
    + invalidate_inode_pages2_range(filp->f_mapping, 0, ~0UL);
    +
    + return 0;
    +}
    +
    +/*
    + * Acquire or release a "no-truncate" lock on *filp.
    + * We overload the S_SWAPFILE flag for loop targets because
    + * it provides the same no-truncate semantics we require, and
    + * holding onto i_sem is no longer an option.
    + */
    +static void file_truncate_lock(struct file *filp)
    +{
    + struct inode *inode = filp->f_mapping->host;
    +
    + mutex_lock(&inode->i_mutex);
    + inode->i_flags |= S_SWAPFILE;
    + mutex_unlock(&inode->i_mutex);
    +}
    +
    +static void file_truncate_unlock(struct file *filp)
    +{
    + struct inode *inode = filp->f_mapping->host;
    +
    + mutex_lock(&inode->i_mutex);
    + inode->i_flags &= ~S_SWAPFILE;
    + mutex_unlock(&inode->i_mutex);
    +}
    +
    +/*
    + * Fill out split_io for taget backing store
    + */
    +static void set_split_io(struct dm_target *ti)
    +{
    + struct loop_c *lc = ti->private;
    +
    + if (test_bit(DM_LOOP_BMAP, &lc->flags))
    + /* Split I/O at block boundaries */
    + ti->split_io = 1 << (lc->blkbits - SECTOR_SHIFT);
    + else
    + ti->split_io = 64;
    +
    + DMDEBUG("splitting io at %llu sector boundaries",
    + (unsigned long long) ti->split_io);
    +}
    +
    +/*
    + * Check that the loop file is regular and available.
    + */
    +static int loop_check_file(struct dm_target *ti)
    +{
    + struct loop_c *lc = ti->private;
    + struct file *filp = lc->filp;
    + struct inode *inode = filp->f_mapping->host;
    +
    + if (!inode)
    + return -ENXIO;
    +
    + ti->error = "backing file must be a regular file";
    + if (!S_ISREG(inode->i_mode))
    + return -EINVAL;
    +
    + ti->error = "backing file is mapped into userspace for writing";
    + if (mapping_writably_mapped(filp->f_mapping))
    + return -EBUSY;
    +
    + if (mapping_mapped(filp->f_mapping))
    + DMWARN("%s is mapped into userspace", lc->path);
    +
    + if (!inode->i_sb || !inode->i_sb->s_bdev) {
    + DMWARN("%s has no blockdevice - switching to filesystem I/O",
    + lc->path);
    + clear_bit(DM_LOOP_BMAP, &lc->flags);
    + set_bit(DM_LOOP_FSIO, &lc->flags);
    + }
    +
    + ti->error = "backing file already in use";
    + if (IS_SWAPFILE(inode))
    + return -EBUSY;
    +
    + return 0;
    +}
    +
    +/*
    + * Check loop file size and store it in the loop context
    + */
    +static int loop_setup_size(struct dm_target *ti)
    +{
    + struct loop_c *lc = ti->private;
    + struct inode *inode = lc->filp->f_mapping->host;
    + int r = -EINVAL;
    +
    + lc->size = i_size_read(inode);
    + lc->blkbits = inode->i_blkbits;
    +
    + ti->error = "backing file is empty";
    + if (!lc->size)
    + goto out;
    +
    + DMDEBUG("set backing file size to %llu", (unsigned long long) lc->size);
    +
    + ti->error = "backing file cannot be less than one block in size";
    + if (lc->size < (blk2sect(lc, 1) << 9))
    + goto out;
    +
    + ti->error = "loop file offset must be a multiple of fs blocksize";
    + if (lc->offset & ((1 << lc->blkbits) - 1))
    + goto out;
    +
    + ti->error = "loop file offset too large";
    + if (lc->offset > (lc->size - (1 << 9)))
    + goto out;
    +
    + lc->mapped_sectors = (lc->size - lc->offset) >> 9;
    + DMDEBUG("set mapped sectors to %llu (%llu bytes)",
    + (unsigned long long) lc->mapped_sectors,
    + (lc->size - lc->offset));
    +
    + if ((lc->offset + (lc->mapped_sectors << 9)) < lc->size)
    + DMWARN("not using %llu bytes in incomplete block at EOF",
    + lc->size - (lc->offset + (lc->mapped_sectors << 9)));
    +
    + ti->error = "mapped region cannot be smaller than target size";
    + if (lc->size - lc->offset < (ti->len << 9))
    + goto out;
    +
    + r = 0;
    +
    +out:
    + return r;
    +}
    +
    +/*
    + * release a loop file
    + */
    +static void loop_put_file(struct file *filp)
    +{
    + if (!filp)
    + return;
    +
    + file_truncate_unlock(filp);
    + filp_close(filp, NULL);
    +}
    +
    +/*
    + * Open loop file and perform type, availability and size checks.
    + */
    +static int loop_get_file(struct dm_target *ti)
    +{
    + int flags = ((dm_table_get_mode(ti->table) & FMODE_WRITE) ?
    + O_RDWR : O_RDONLY) | O_LARGEFILE;
    + struct loop_c *lc = ti->private;
    + struct file *filp;
    + int r = 0;
    +
    + ti->error = "could not open backing file";
    + filp = filp_open(lc->path, flags, 0);
    + if (IS_ERR(filp))
    + return PTR_ERR(filp);
    + lc->filp = filp;
    + r = loop_check_file(ti);
    + if (r)
    + goto err;
    +
    + r = loop_setup_size(ti);
    + if (r)
    + goto err;
    +
    + file_truncate_lock(filp);
    + return 0;
    +
    +err:
    + fput(filp);
    + return r;
    +}
    +
    +/*
    + * invalidate mapped pages belonging to the loop file
    + */
    +static void loop_flush(struct dm_target *ti)
    +{
    + struct loop_c *lc = ti->private;
    +
    + loop_invalidate_file(lc->filp);
    +}
    +
    +/*--------------------------------------------------------------------
    + * Device-mapper target methods
    + *--------------------------------------------------------------------*/
    +
    +/*
    + * Generic loop map function. Re-base I/O to target begin and submit
    + */
    +static int loop_map(struct dm_target *ti, struct bio *bio,
    + union map_info *context)
    +{
    + struct loop_c *lc = ti->private;
    +
    + if (unlikely(bio_barrier(bio)))
    + return -EOPNOTSUPP;
    +
    + bio->bi_sector -= ti->begin;
    +
    + if (lc->map_fn)
    + return lc->map_fn(ti, bio);
    +
    + return -EIO;
    +}
    +
    +/*
    + * Block status helper
    + */
    +static ssize_t loop_file_status(struct loop_c *lc, char *result,
    + unsigned maxlen)
    +{
    + ssize_t sz = 0;
    + struct file_map_c *fc = lc->map_data;
    + int qlen;
    +
    + spin_lock_irq(&fc->lock);
    + qlen = bio_list_size(&fc->work);
    + qlen += bio_list_size(&fc->in);
    + spin_unlock_irq(&fc->lock);
    +
    + DMEMIT("file %d", qlen);
    +
    + return sz;
    +}
    +
    +/*
    + * File status helper
    + */
    +static ssize_t loop_block_status(struct loop_c *lc, char *result,
    + unsigned maxlen)
    +{
    + ssize_t sz = 0;
    + struct block_map_c *bc = lc->map_data;
    + int mru;
    +
    + spin_lock_irq(&bc->mru_lock);
    + mru = bc->mru - bc->map;
    + spin_unlock_irq(&bc->mru_lock);
    +
    + DMEMIT("block %d %d", bc->nr_extents, mru);
    +
    + return sz;
    +}
    +
    +/*
    + * This needs some thought on handling unlinked backing files. some parts of
    + * the kernel return a cached name (now invalid), while others return a dcache
    + * "/path/to/foo (deleted)" name (never was/is valid). Which is "better" is
    + * debatable.
    + *
    + * On the one hand, using a cached name gives table output which is directly
    + * usable assuming the user re-creates the unlinked image file, on the other
    + * it is more consistent with e.g. swap to use the dcache name.
    + *
    +*/
    +static int loop_status(struct dm_target *ti, status_type_t type, char *result,
    + unsigned maxlen)
    +{
    + struct loop_c *lc = ti->private;
    + ssize_t sz = 0;
    +
    + switch (type) {
    + case STATUSTYPE_INFO:
    + if (test_bit(DM_LOOP_BMAP, &lc->flags))
    + sz += loop_block_status(lc, result, maxlen - sz);
    + else if (test_bit(DM_LOOP_FSIO, &lc->flags))
    + sz += loop_file_status(lc, result, maxlen - sz);
    + break;
    +
    + case STATUSTYPE_TABLE:
    + DMEMIT("%s %llu", lc->path, lc->offset);
    + break;
    + }
    + return 0;
    +}
    +
    +/*
    + * Destroy a loopback mapping
    + */
    +static void loop_dtr(struct dm_target *ti)
    +{
    + struct loop_c *lc = ti->private;
    +
    + if ((dm_table_get_mode(ti->table) & FMODE_WRITE))
    + loop_invalidate_file(lc->filp);
    +
    + if (test_bit(DM_LOOP_BMAP, &lc->flags) && lc->map_data)
    + destroy_block_map((struct block_map_c *)lc->map_data);
    + if (test_bit(DM_LOOP_FSIO, &lc->flags) && lc->map_data)
    + destroy_file_map(lc);
    +
    + loop_put_file(lc->filp);
    + DMINFO("released file %s", lc->path);
    +
    + kfree(lc);
    +}
    +
    +/*
    + * Construct a loopback mapping: <path> <offset>
    + */
    +static int loop_ctr(struct dm_target *ti, unsigned argc, char **argv)
    +{
    + struct loop_c *lc = NULL;
    + int r = -EINVAL;
    +
    + ti->error = "invalid argument count";
    + if (argc != 2)
    + goto err;
    +
    + r = -ENOMEM;
    + ti->error = "cannot allocate loop context";
    + lc = kzalloc(sizeof(*lc), GFP_KERNEL);
    + if (!lc)
    + goto err;
    +
    + /* default */
    + set_bit(DM_LOOP_BMAP, &lc->flags);
    + ti->error = "cannot allocate loop path";
    + lc->path = kstrdup(argv[0], GFP_KERNEL);
    + if (!lc->path)
    + goto err;
    +
    + ti->private = lc;
    +
    + r = -EINVAL;
    + ti->error = "invalid file offset";
    + if (sscanf(argv[1], "%lld", &lc->offset) != 1)
    + goto err;
    +
    + if (lc->offset)
    + DMDEBUG("setting file offset to %lld", lc->offset);
    +
    + /* open & check file and set size parameters */
    + r = loop_get_file(ti);
    +
    + /* ti->error has been set by loop_get_file */
    + if (r)
    + goto err;
    +
    + ti->error = "could not create loop mapping";
    + if (test_bit(DM_LOOP_BMAP, &lc->flags))
    + r = setup_block_map(lc, lc->filp->f_mapping->host);
    + if (test_bit(DM_LOOP_FSIO, &lc->flags))
    + r = setup_file_map(lc);
    +
    + if (r)
    + goto err_putf;
    +
    + loop_invalidate_file(lc->filp);
    +
    + set_split_io(ti);
    + if (lc->bdev)
    + dm_set_device_limits(ti, lc->bdev);
    +
    + DMDEBUG("constructed loop target on %s "
    + "(%lldk, %llu sectors)", lc->path,
    + (lc->size >> 10), (unsigned long long)lc->mapped_sectors);
    + ti->error = NULL;
    +
    + return 0;
    +
    +err_putf:
    + loop_put_file(lc->filp);
    +err:
    + if (lc)
    + kfree(lc);
    + return r;
    +}
    +
    +static struct target_type loop_target = {
    + .name = "loop",
    + .version = {0, 0, 2},
    + .module = THIS_MODULE,
    + .ctr = loop_ctr,
    + .dtr = loop_dtr,
    + .map = loop_map,
    + .presuspend = loop_flush,
    + .flush = loop_flush,
    + .status = loop_status,
    +};
    +
    +/*--------------------------------------------------------------------
    + * Module bits
    + *--------------------------------------------------------------------*/
    +static int __init dm_loop_init(void)
    +{
    + int r;
    +
    + r = dm_register_target(&loop_target);
    + if (r < 0) {
    + DMERR("register failed %d", r);
    + goto err;
    + }
    +
    + r = -ENOMEM;
    + dm_loop_extent_cache = KMEM_CACHE(dm_loop_extent, SLAB_HWCACHE_ALIGN);
    + if (!dm_loop_extent_cache)
    + goto err;
    +
    + DMINFO("version %u.%u.%u loaded",
    + loop_target.version[0], loop_target.version[1],
    + loop_target.version[2]);
    +
    + return 0;
    +
    +err:
    + if (dm_loop_extent_cache)
    + kmem_cache_destroy(dm_loop_extent_cache);
    +
    + return r;
    +}
    +
    +static void __exit dm_loop_exit(void)
    +{
    + int r;
    +
    + r = dm_unregister_target(&loop_target);
    + kmem_cache_destroy(dm_loop_extent_cache);
    +
    + if (r < 0)
    + DMERR("target unregister failed %d", r);
    + else
    + DMINFO("version %u.%u.%u unloaded",
    + loop_target.version[0], loop_target.version[1],
    + loop_target.version[2]);
    +}
    +
    +module_init(dm_loop_init);
    +module_exit(dm_loop_exit);
    +
    +MODULE_LICENSE("GPL");
    +MODULE_AUTHOR("Bryn Reeves <breeves@redhat.com>");
    +MODULE_DESCRIPTION("device-mapper loop target");

    \
     
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      Last update: 2008-01-10 00:21    [W:0.084 / U:13.280 seconds]
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