dm exception store: refactor zero_area

Use a separate buffer for writing zeroes to the on-disk snapshot
exception store, make the updating of ps->current_area explicit and
refactor the code in preparation for the fix in the next patch.

No functional change.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org

1 files changed, 68 insertions, 34 deletions

diff --git a/drivers/md/dm-exception-store.c b/drivers/md/dm-exception-store.c
index 769ab677f8e0..fe6cef8df203 100644
--- a/drivers/md/dm-exception-store.c
+++ b/drivers/md/dm-exception-store.c
@@ -105,6 +105,11 @@ struct pstore {
         void *area;
 
         /*
+         * An area of zeros used to clear the next area.
+         */
+        void *zero_area;
+
+        /*
          * Used to keep track of which metadata area the data in
          * 'chunk' refers to.
          */
@@ -149,6 +154,13 @@ static int alloc_area(struct pstore *ps)
         if (!ps->area)
                 return r;
 
+        ps->zero_area = vmalloc(len);
+        if (!ps->zero_area) {
+                vfree(ps->area);
+                return r;
+        }
+        memset(ps->zero_area, 0, len);
+
         return 0;
 }
 
@@ -156,6 +168,8 @@ static void free_area(struct pstore *ps)
 {
         vfree(ps->area);
         ps->area = NULL;
+        vfree(ps->zero_area);
+        ps->zero_area = NULL;
 }
 
 struct mdata_req {
@@ -220,25 +234,41 @@ static chunk_t area_location(struct pstore *ps, chunk_t area)
  * Read or write a metadata area.  Remembering to skip the first
  * chunk which holds the header.
  */
-static int area_io(struct pstore *ps, chunk_t area, int rw)
+static int area_io(struct pstore *ps, int rw)
 {
         int r;
         chunk_t chunk;
 
-        chunk = area_location(ps, area);
+        chunk = area_location(ps, ps->current_area);
 
         r = chunk_io(ps, chunk, rw, 0);
         if (r)
                 return r;
 
-        ps->current_area = area;
         return 0;
 }
 
-static int zero_area(struct pstore *ps, chunk_t area)
+static void zero_memory_area(struct pstore *ps)
 {
         memset(ps->area, 0, ps->snap->chunk_size << SECTOR_SHIFT);
-        return area_io(ps, area, WRITE);
+}
+
+static int zero_disk_area(struct pstore *ps, chunk_t area)
+{
+        struct dm_io_region where = {
+                .bdev = ps->snap->cow->bdev,
+                .sector = ps->snap->chunk_size * area_location(ps, area),
+                .count = ps->snap->chunk_size,
+        };
+        struct dm_io_request io_req = {
+                .bi_rw = WRITE,
+                .mem.type = DM_IO_VMA,
+                .mem.ptr.vma = ps->zero_area,
+                .client = ps->io_client,
+                .notify.fn = NULL,
+        };
+
+        return dm_io(&io_req, 1, &where, NULL);
 }
 
 static int read_header(struct pstore *ps, int *new_snapshot)
@@ -411,15 +441,14 @@ static int insert_exceptions(struct pstore *ps, int *full)
 
 static int read_exceptions(struct pstore *ps)
 {
-        chunk_t area;
         int r, full = 1;
 
         /*
          * Keeping reading chunks and inserting exceptions until
          * we find a partially full area.
          */
-        for (area = 0; full; area++) {
-                r = area_io(ps, area, READ);
+        for (ps->current_area = 0; full; ps->current_area++) {
+                r = area_io(ps, READ);
                 if (r)
                         return r;
 
@@ -428,6 +457,8 @@ static int read_exceptions(struct pstore *ps)
                         return r;
         }
 
+        ps->current_area--;
+
         return 0;
 }
 
@@ -486,12 +517,13 @@ static int persistent_read_metadata(struct exception_store *store)
                         return r;
                 }
 
-                r = zero_area(ps, 0);
+                ps->current_area = 0;
+                zero_memory_area(ps);
+                r = zero_disk_area(ps, 0);
                 if (r) {
-                        DMWARN("zero_area(0) failed");
+                        DMWARN("zero_disk_area(0) failed");
                         return r;
                 }
-
         } else {
                 /*
                  * Sanity checks.
@@ -551,7 +583,6 @@ static void persistent_commit(struct exception_store *store,
                               void (*callback) (void *, int success),
                               void *callback_context)
 {
-        int r;
         unsigned int i;
         struct pstore *ps = get_info(store);
         struct disk_exception de;
@@ -572,33 +603,36 @@ static void persistent_commit(struct exception_store *store,
         cb->context = callback_context;
 
         /*
-         * If there are no more exceptions in flight, or we have
-         * filled this metadata area we commit the exceptions to
-         * disk.
+         * If there are exceptions in flight and we have not yet
+         * filled this metadata area there's nothing more to do.
          */
-        if (atomic_dec_and_test(&ps->pending_count) ||
-            (ps->current_committed == ps->exceptions_per_area)) {
-                r = area_io(ps, ps->current_area, WRITE);
-                if (r)
-                        ps->valid = 0;
+        if (!atomic_dec_and_test(&ps->pending_count) &&
+            (ps->current_committed != ps->exceptions_per_area))
+                return;
 
-                /*
-                 * Have we completely filled the current area ?
-                 */
-                if (ps->current_committed == ps->exceptions_per_area) {
-                        ps->current_committed = 0;
-                        r = zero_area(ps, ps->current_area + 1);
-                        if (r)
-                                ps->valid = 0;
-                }
+        /*
+         * Commit exceptions to disk.
+         */
+        if (area_io(ps, WRITE))
+                ps->valid = 0;
 
-                for (i = 0; i < ps->callback_count; i++) {
-                        cb = ps->callbacks + i;
-                        cb->callback(cb->context, r == 0 ? 1 : 0);
-                }
+        /*
+         * Advance to the next area if this one is full.
+         */
+        if (ps->current_committed == ps->exceptions_per_area) {
+                if (zero_disk_area(ps, ps->current_area + 1))
+                        ps->valid = 0;
+                ps->current_committed = 0;
+                ps->current_area++;
+                zero_memory_area(ps);
+        }
 
-                ps->callback_count = 0;
+        for (i = 0; i < ps->callback_count; i++) {
+                cb = ps->callbacks + i;
+                cb->callback(cb->context, ps->valid);
         }
+
+        ps->callback_count = 0;
 }
 
 static void persistent_drop(struct exception_store *store)