Now that the exception store implementations are capable of
caching the exceptions on their own, we need a new function
added to the API to allow us to lookup the exceptions.

Adding 'lookup_exception' to the exception store API.

RFC-by: Jonathan Brassow <jbrassow@redhat.com>

Index: linux-2.6/drivers/md/dm-exception-store.h
================================================== =================
--- linux-2.6.orig/drivers/md/dm-exception-store.h
+++ linux-2.6/drivers/md/dm-exception-store.h
@@ -58,6 +58,16 @@ struct dm_exception_store_type {
void *callback_context);

/*
+ * Look up an exception. For certain exception stores,
+ * this function /may/ block. The caller must specify whether
+ * they can tolerate this. If the function would block and the
+ * user specified can_block=0, -EWOULDBLK will be returned.
+ */
+ int (*lookup_exception) (struct dm_exception_store *store,
+ struct dm_exception **e,
+ chunk_t old, int can_block);
+
+ /*
* The snapshot is invalid, note this in the metadata.
*/
void (*drop_snapshot) (struct dm_exception_store *store);
Index: linux-2.6/drivers/md/dm-snap-persistent.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap-persistent.c
+++ linux-2.6/drivers/md/dm-snap-persistent.c
@@ -711,6 +711,17 @@ static void persistent_commit_exception(
ps->callback_count = 0;
}

+static int persistent_lookup_exception(struct dm_exception_store *store,
+ struct dm_exception **e,
+ chunk_t old, int can_block)
+{
+ struct pstore *ps = get_info(store);
+
+ *e = dm_lookup_exception(ps->table, old);
+
+ return 0;
+}
+
static void persistent_drop_snapshot(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
@@ -803,6 +814,7 @@ static struct dm_exception_store_type _p
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
+ .lookup_exception = persistent_lookup_exception,
.drop_snapshot = persistent_drop_snapshot,
.fraction_full = persistent_fraction_full,
.status = persistent_status,
@@ -817,6 +829,7 @@ static struct dm_exception_store_type _p
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
+ .lookup_exception = persistent_lookup_exception,
.drop_snapshot = persistent_drop_snapshot,
.fraction_full = persistent_fraction_full,
.status = persistent_status,
Index: linux-2.6/drivers/md/dm-snap-transient.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap-transient.c
+++ linux-2.6/drivers/md/dm-snap-transient.c
@@ -94,6 +94,17 @@ static void transient_commit_exception(s
callback(callback_context, 1);
}

+static int transient_lookup_exception(struct dm_exception_store *store,
+ struct dm_exception **e,
+ chunk_t old, int can_block)
+{
+ struct transient_c *tc = store->context;
+
+ *e = dm_lookup_exception(tc->table, old);
+
+ return 0;
+}
+
static void transient_fraction_full(struct dm_exception_store *store,
sector_t *numerator, sector_t *denominator)
{
@@ -165,6 +176,7 @@ static struct dm_exception_store_type _t
.read_metadata = transient_read_metadata,
.prepare_exception = transient_prepare_exception,
.commit_exception = transient_commit_exception,
+ .lookup_exception = transient_lookup_exception,
.fraction_full = transient_fraction_full,
.status = transient_status,
};
@@ -178,6 +190,7 @@ static struct dm_exception_store_type _t
.read_metadata = transient_read_metadata,
.prepare_exception = transient_prepare_exception,
.commit_exception = transient_commit_exception,
+ .lookup_exception = transient_lookup_exception,
.fraction_full = transient_fraction_full,
.status = transient_status,
};
Index: linux-2.6/drivers/md/dm-snap.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap.c
+++ linux-2.6/drivers/md/dm-snap.c
@@ -994,7 +994,7 @@ static int snapshot_map(struct dm_target
{
struct dm_exception *e;
struct dm_snapshot *s = ti->private;
- int r = DM_MAPIO_REMAPPED;
+ int rtn, r = DM_MAPIO_REMAPPED;
chunk_t chunk;
struct dm_snap_pending_exception *pe = NULL;

@@ -1015,7 +1015,15 @@ static int snapshot_map(struct dm_target
}

/* If the block is already remapped - use that, else remap it */
- e = dm_lookup_exception(s->complete, chunk);
+ rtn = s->store->type->lookup_exception(s->store, &e, chunk, 0);
+ if (rtn) {
+ /*
+ * Could be -EWOULDBLOCK, but we don't handle that yet
+ * and there are currently no exception store
+ * implementations that would require us to.
+ */
+ BUG();
+ }
if (e) {
remap_exception(s, e, bio, chunk);
goto out_unlock;
@@ -1134,7 +1142,7 @@ static int snapshot_status(struct dm_tar
*---------------------------------------------------------------*/
static int __origin_write(struct list_head *snapshots, struct bio *bio)
{
- int r = DM_MAPIO_REMAPPED, first = 0;
+ int rtn, r = DM_MAPIO_REMAPPED, first = 0;
struct dm_snapshot *snap;
struct dm_exception *e;
struct dm_snap_pending_exception *pe, *next_pe, *primary_pe = NULL;
@@ -1168,7 +1176,16 @@ static int __origin_write(struct list_he
* ref_count is initialised to 1 so pending_complete()
* won't destroy the primary_pe while we're inside this loop.
*/
- e = dm_lookup_exception(snap->complete, chunk);
+ rtn = snap->store->type->lookup_exception(snap->store, &e,
+ chunk, 0);
+ if (rtn) {
+ /*
+ * Could be -EWOULDBLOCK, but we don't handle that yet
+ * and there are currently no exception store
+ * implementations that would require us to.
+ */
+ BUG();
+ }
if (e)
goto next_snapshot;



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Now that the exception store implementations are capable of
caching the exceptions on their own, we need a new function
added to the API to allow us to lookup the exceptions.

Adding 'lookup_exception' to the exception store API.

RFC-by: Jonathan Brassow <jbrassow@redhat.com>

Index: linux-2.6/drivers/md/dm-exception-store.h
================================================== =================
--- linux-2.6.orig/drivers/md/dm-exception-store.h
+++ linux-2.6/drivers/md/dm-exception-store.h
@@ -58,6 +58,18 @@ struct dm_exception_store_type {
void *callback_context);

/*
+ * Look up an exception. Common errors include:
+ * -ENOENT : exception not found
+ * -EWOULDBLOCK: blocking op required and can_block=0
+ *
+ * If 'new_chunk' is NULL, the caller simply wants to
+ * know if the exception exists (0) or not (-ENOENT).
+ */
+ int (*lookup_exception) (struct dm_exception_store *store,
+ chunk_t old, chunk_t *new_chunk,
+ int can_block);
+
+ /*
* The snapshot is invalid, note this in the metadata.
*/
void (*drop_snapshot) (struct dm_exception_store *store);
Index: linux-2.6/drivers/md/dm-snap-persistent.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap-persistent.c
+++ linux-2.6/drivers/md/dm-snap-persistent.c
@@ -721,6 +721,23 @@ static void persistent_commit_exception(
ps->callback_count = 0;
}

+static int persistent_lookup_exception(struct dm_exception_store *store,
+ chunk_t old, chunk_t *new_chunk,
+ int can_block)
+{
+ struct pstore *ps = get_info(store);
+ struct dm_exception *e;
+
+ e = dm_lookup_exception(ps->table, old);
+ if (!e)
+ return -ENOENT;
+
+ if (new_chunk)
+ *new_chunk = e->new_chunk + (old - e->old_chunk);
+
+ return 0;
+}
+
static void persistent_drop_snapshot(struct dm_exception_store *store)
{
struct pstore *ps = get_info(store);
@@ -813,6 +830,7 @@ static struct dm_exception_store_type _p
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
+ .lookup_exception = persistent_lookup_exception,
.drop_snapshot = persistent_drop_snapshot,
.fraction_full = persistent_fraction_full,
.status = persistent_status,
@@ -827,6 +845,7 @@ static struct dm_exception_store_type _p
.read_metadata = persistent_read_metadata,
.prepare_exception = persistent_prepare_exception,
.commit_exception = persistent_commit_exception,
+ .lookup_exception = persistent_lookup_exception,
.drop_snapshot = persistent_drop_snapshot,
.fraction_full = persistent_fraction_full,
.status = persistent_status,
Index: linux-2.6/drivers/md/dm-snap-transient.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap-transient.c
+++ linux-2.6/drivers/md/dm-snap-transient.c
@@ -94,6 +94,23 @@ static void transient_commit_exception(s
callback(callback_context, 1);
}

+static int transient_lookup_exception(struct dm_exception_store *store,
+ chunk_t old, chunk_t *new_chunk,
+ int can_block)
+{
+ struct transient_c *tc = store->context;
+ struct dm_exception *e;
+
+ e = dm_lookup_exception(tc->table, old);
+ if (!e)
+ return -ENOENT;
+
+ if (new_chunk)
+ *new_chunk = e->new_chunk + (old - e->old_chunk);
+
+ return 0;
+}
+
static void transient_fraction_full(struct dm_exception_store *store,
sector_t *numerator, sector_t *denominator)
{
@@ -165,6 +182,7 @@ static struct dm_exception_store_type _t
.read_metadata = transient_read_metadata,
.prepare_exception = transient_prepare_exception,
.commit_exception = transient_commit_exception,
+ .lookup_exception = transient_lookup_exception,
.fraction_full = transient_fraction_full,
.status = transient_status,
};
@@ -178,6 +196,7 @@ static struct dm_exception_store_type _t
.read_metadata = transient_read_metadata,
.prepare_exception = transient_prepare_exception,
.commit_exception = transient_commit_exception,
+ .lookup_exception = transient_lookup_exception,
.fraction_full = transient_fraction_full,
.status = transient_status,
};
Index: linux-2.6/drivers/md/dm-snap.c
================================================== =================
--- linux-2.6.orig/drivers/md/dm-snap.c
+++ linux-2.6/drivers/md/dm-snap.c
@@ -979,24 +979,19 @@ out:
return pe;
}

-static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
- struct bio *bio, chunk_t chunk)
+static void remap_exception(struct dm_snapshot *s, struct bio *bio, chunk_t chunk)
{
bio->bi_bdev = s->store->cow->bdev;
- bio->bi_sector = chunk_to_sector(s->store,
- dm_chunk_number(e->new_chunk) +
- (chunk - e->old_chunk)) +
- (bio->bi_sector &
- s->store->chunk_mask);
+ bio->bi_sector = chunk_to_sector(s->store, dm_chunk_number(chunk)) +
+ (bio->bi_sector & s->store->chunk_mask);
}

static int snapshot_map(struct dm_target *ti, struct bio *bio,
union map_info *map_context)
{
- struct dm_exception *e;
struct dm_snapshot *s = ti->private;
- int r = DM_MAPIO_REMAPPED;
- chunk_t chunk;
+ int rtn, r = DM_MAPIO_REMAPPED;
+ chunk_t chunk, new_chunk;
struct dm_snap_pending_exception *pe = NULL;

chunk = sector_to_chunk(s->store, bio->bi_sector);
@@ -1016,13 +1011,20 @@ static int snapshot_map(struct dm_target
}

/* If the block is already remapped - use that, else remap it */
- e = dm_lookup_exception(s->complete, chunk);
- if (e) {
- remap_exception(s, e, bio, chunk);
+ rtn = s->store->type->lookup_exception(s->store, chunk, &new_chunk, 0);
+ if (!rtn) {
+ remap_exception(s, bio, new_chunk);
goto out_unlock;
}

/*
+ * Could be -EWOULDBLOCK, but we don't handle that yet
+ * and there are currently no exception store
+ * implementations that would require us to.
+ */
+ BUG_ON(rtn != -ENOENT);
+
+ /*
* Write to snapshot - higher level takes care of RW/RO
* flags so we should only get this if we are
* writeable.
@@ -1035,7 +1037,7 @@ static int snapshot_map(struct dm_target
goto out_unlock;
}

- remap_exception(s, &pe->e, bio, chunk);
+ remap_exception(s, bio, pe->e.new_chunk);
bio_list_add(&pe->snapshot_bios, bio);

r = DM_MAPIO_SUBMITTED;
@@ -1136,9 +1138,8 @@ static int snapshot_status(struct dm_tar
*---------------------------------------------------------------*/
static int __origin_write(struct list_head *snapshots, struct bio *bio)
{
- int r = DM_MAPIO_REMAPPED, first = 0;
+ int rtn, r = DM_MAPIO_REMAPPED, first = 0;
struct dm_snapshot *snap;
- struct dm_exception *e;
struct dm_snap_pending_exception *pe, *next_pe, *primary_pe = NULL;
chunk_t chunk;
LIST_HEAD(pe_queue);
@@ -1170,10 +1171,18 @@ static int __origin_write(struct list_he
* ref_count is initialised to 1 so pending_complete()
* won't destroy the primary_pe while we're inside this loop.
*/
- e = dm_lookup_exception(snap->complete, chunk);
- if (e)
+ rtn = snap->store->type->lookup_exception(snap->store, chunk,
+ NULL, 0);
+ if (!rtn)
goto next_snapshot;

+ /*
+ * Could be -EWOULDBLOCK, but we don't handle that yet
+ * and there are currently no exception store
+ * implementations that would require us to.
+ */
+ BUG_ON(rtn != -ENOENT);
+
pe = __find_pending_exception(snap, bio);
if (!pe) {
__invalidate_snapshot(snap, -ENOMEM);

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