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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    [from the cache]
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