dm thin: prepare to support discard

This patch contains the ground work needed for dm-thin to support discard.

  - Adds endio function that replaces shared_read_endio.

  - Introduce an explicit 'quiesced' flag into the new_mapping structure.
    Before, this was implicitly indicated by m->list being empty.

  - The map_info->ptr remains constant for the duration of a bio's trip
    through the thin target.  Make it easier to reason about it.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 72 insertions, 53 deletions

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 7ca2bf2aafaa..188121ca00aa 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -523,7 +523,7 @@ struct pool {
 
         struct bio_list retry_on_resume_list;
 
-        struct deferred_set ds; /* FIXME: move to thin_c */
+        struct deferred_set shared_read_ds;
 
         struct new_mapping *next_mapping;
         mempool_t *mapping_pool;
@@ -618,6 +618,12 @@ static struct pool *__pool_table_lookup_metadata_dev(struct block_device *md_dev
 
 /*----------------------------------------------------------------*/
 
+struct endio_hook {
+        struct thin_c *tc;
+        struct deferred_entry *shared_read_entry;
+        struct new_mapping *overwrite_mapping;
+};
+
 static void __requeue_bio_list(struct thin_c *tc, struct bio_list *master)
 {
         struct bio *bio;
@@ -628,7 +634,8 @@ static void __requeue_bio_list(struct thin_c *tc, struct bio_list *master)
         bio_list_init(master);
 
         while ((bio = bio_list_pop(&bios))) {
-                if (dm_get_mapinfo(bio)->ptr == tc)
+                struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+                if (h->tc == tc)
                         bio_endio(bio, DM_ENDIO_REQUEUE);
                 else
                         bio_list_add(master, bio);
@@ -716,16 +723,11 @@ static void wake_worker(struct pool *pool)
 /*
  * Bio endio functions.
  */
-struct endio_hook {
-        struct thin_c *tc;
-        bio_end_io_t *saved_bi_end_io;
-        struct deferred_entry *entry;
-};
-
 struct new_mapping {
         struct list_head list;
 
-        int prepared;
+        unsigned quiesced:1;
+        unsigned prepared:1;
 
         struct thin_c *tc;
         dm_block_t virt_block;
@@ -747,7 +749,7 @@ static void __maybe_add_mapping(struct new_mapping *m)
 {
         struct pool *pool = m->tc->pool;
 
-        if (list_empty(&m->list) && m->prepared) {
+        if (m->quiesced && m->prepared) {
                 list_add(&m->list, &pool->prepared_mappings);
                 wake_worker(pool);
         }
@@ -770,7 +772,8 @@ static void copy_complete(int read_err, unsigned long write_err, void *context)
 static void overwrite_endio(struct bio *bio, int err)
 {
         unsigned long flags;
-        struct new_mapping *m = dm_get_mapinfo(bio)->ptr;
+        struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+        struct new_mapping *m = h->overwrite_mapping;
         struct pool *pool = m->tc->pool;
 
         m->err = err;
@@ -781,31 +784,6 @@ static void overwrite_endio(struct bio *bio, int err)
         spin_unlock_irqrestore(&pool->lock, flags);
 }
 
-static void shared_read_endio(struct bio *bio, int err)
-{
-        struct list_head mappings;
-        struct new_mapping *m, *tmp;
-        struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
-        unsigned long flags;
-        struct pool *pool = h->tc->pool;
-
-        bio->bi_end_io = h->saved_bi_end_io;
-        bio_endio(bio, err);
-
-        INIT_LIST_HEAD(&mappings);
-        ds_dec(h->entry, &mappings);
-
-        spin_lock_irqsave(&pool->lock, flags);
-        list_for_each_entry_safe(m, tmp, &mappings, list) {
-                list_del(&m->list);
-                INIT_LIST_HEAD(&m->list);
-                __maybe_add_mapping(m);
-        }
-        spin_unlock_irqrestore(&pool->lock, flags);
-
-        mempool_free(h, pool->endio_hook_pool);
-}
-
 /*----------------------------------------------------------------*/
 
 /*
@@ -957,6 +935,7 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
         struct new_mapping *m = get_next_mapping(pool);
 
         INIT_LIST_HEAD(&m->list);
+        m->quiesced = 0;
         m->prepared = 0;
         m->tc = tc;
         m->virt_block = virt_block;
@@ -965,7 +944,8 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
         m->err = 0;
         m->bio = NULL;
 
-        ds_add_work(&pool->ds, &m->list);
+        if (!ds_add_work(&pool->shared_read_ds, &m->list))
+                m->quiesced = 1;
 
         /*
          * IO to pool_dev remaps to the pool target's data_dev.
@@ -974,9 +954,10 @@ static void schedule_copy(struct thin_c *tc, dm_block_t virt_block,
          * bio immediately. Otherwise we use kcopyd to clone the data first.
          */
         if (io_overwrites_block(pool, bio)) {
+                struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+                h->overwrite_mapping = m;
                 m->bio = bio;
                 save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
-                dm_get_mapinfo(bio)->ptr = m;
                 remap_and_issue(tc, bio, data_dest);
         } else {
                 struct dm_io_region from, to;
@@ -1023,6 +1004,7 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
         struct new_mapping *m = get_next_mapping(pool);
 
         INIT_LIST_HEAD(&m->list);
+        m->quiesced = 1;
         m->prepared = 0;
         m->tc = tc;
         m->virt_block = virt_block;
@@ -1040,9 +1022,10 @@ static void schedule_zero(struct thin_c *tc, dm_block_t virt_block,
                 process_prepared_mapping(m);
 
         else if (io_overwrites_block(pool, bio)) {
+                struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+                h->overwrite_mapping = m;
                 m->bio = bio;
                 save_and_set_endio(bio, &m->saved_bi_end_io, overwrite_endio);
-                dm_get_mapinfo(bio)->ptr = m;
                 remap_and_issue(tc, bio, data_block);
 
         } else {
@@ -1129,7 +1112,8 @@ static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
  */
 static void retry_on_resume(struct bio *bio)
 {
-        struct thin_c *tc = dm_get_mapinfo(bio)->ptr;
+        struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+        struct thin_c *tc = h->tc;
         struct pool *pool = tc->pool;
         unsigned long flags;
 
@@ -1195,13 +1179,9 @@ static void process_shared_bio(struct thin_c *tc, struct bio *bio,
         if (bio_data_dir(bio) == WRITE)
                 break_sharing(tc, bio, block, &key, lookup_result, cell);
         else {
-                struct endio_hook *h;
-                h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);
+                struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
 
-                h->tc = tc;
-                h->entry = ds_inc(&pool->ds);
-                save_and_set_endio(bio, &h->saved_bi_end_io, shared_read_endio);
-                dm_get_mapinfo(bio)->ptr = h;
+                h->shared_read_entry = ds_inc(&pool->shared_read_ds);
 
                 cell_release_singleton(cell, bio);
                 remap_and_issue(tc, bio, lookup_result->block);
@@ -1325,7 +1305,9 @@ static void process_deferred_bios(struct pool *pool)
         spin_unlock_irqrestore(&pool->lock, flags);
 
         while ((bio = bio_list_pop(&bios))) {
-                struct thin_c *tc = dm_get_mapinfo(bio)->ptr;
+                struct endio_hook *h = dm_get_mapinfo(bio)->ptr;
+                struct thin_c *tc = h->tc;
+
                 /*
                  * If we've got no free new_mapping structs, and processing
                  * this bio might require one, we pause until there are some
@@ -1408,6 +1390,18 @@ static void thin_defer_bio(struct thin_c *tc, struct bio *bio)
         wake_worker(pool);
 }
 
+static struct endio_hook *thin_hook_bio(struct thin_c *tc, struct bio *bio)
+{
+        struct pool *pool = tc->pool;
+        struct endio_hook *h = mempool_alloc(pool->endio_hook_pool, GFP_NOIO);
+
+        h->tc = tc;
+        h->shared_read_entry = NULL;
+        h->overwrite_mapping = NULL;
+
+        return h;
+}
+
 /*
  * Non-blocking function called from the thin target's map function.
  */
@@ -1420,11 +1414,7 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio,
         struct dm_thin_device *td = tc->td;
         struct dm_thin_lookup_result result;
 
-        /*
-         * Save the thin context for easy access from the deferred bio later.
-         */
-        map_context->ptr = tc;
-
+        map_context->ptr = thin_hook_bio(tc, bio);
         if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
                 thin_defer_bio(tc, bio);
                 return DM_MAPIO_SUBMITTED;
@@ -1604,7 +1594,7 @@ static struct pool *pool_create(struct mapped_device *pool_md,
         pool->low_water_triggered = 0;
         pool->no_free_space = 0;
         bio_list_init(&pool->retry_on_resume_list);
-        ds_init(&pool->ds);
+        ds_init(&pool->shared_read_ds);
 
         pool->next_mapping = NULL;
         pool->mapping_pool =
@@ -2394,6 +2384,34 @@ static int thin_map(struct dm_target *ti, struct bio *bio,
         return thin_bio_map(ti, bio, map_context);
 }
 
+static int thin_endio(struct dm_target *ti,
+                      struct bio *bio, int err,
+                      union map_info *map_context)
+{
+        unsigned long flags;
+        struct endio_hook *h = map_context->ptr;
+        struct list_head work;
+        struct new_mapping *m, *tmp;
+        struct pool *pool = h->tc->pool;
+
+        if (h->shared_read_entry) {
+                INIT_LIST_HEAD(&work);
+                ds_dec(h->shared_read_entry, &work);
+
+                spin_lock_irqsave(&pool->lock, flags);
+                list_for_each_entry_safe(m, tmp, &work, list) {
+                        list_del(&m->list);
+                        m->quiesced = 1;
+                        __maybe_add_mapping(m);
+                }
+                spin_unlock_irqrestore(&pool->lock, flags);
+        }
+
+        mempool_free(h, pool->endio_hook_pool);
+
+        return 0;
+}
+
 static void thin_postsuspend(struct dm_target *ti)
 {
         if (dm_noflush_suspending(ti))
@@ -2481,6 +2499,7 @@ static struct target_type thin_target = {
         .ctr = thin_ctr,
         .dtr = thin_dtr,
         .map = thin_map,
+        .end_io = thin_endio,
         .postsuspend = thin_postsuspend,
         .status = thin_status,
         .iterate_devices = thin_iterate_devices,