dm table: validate device logical_block_size

Impose necessary and sufficient conditions on a devices's table such
that any incoming bio which respects its logical_block_size can be
processed successfully.

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

1 files changed, 69 insertions, 0 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 535fdaf2473d..e3bcfb8b15a1 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -724,6 +724,71 @@ static void check_for_valid_limits(struct io_restrictions *rs)
                 rs->bounce_pfn = -1;
 }
 
+/*
+ * Impose necessary and sufficient conditions on a devices's table such
+ * that any incoming bio which respects its logical_block_size can be
+ * processed successfully.  If it falls across the boundary between
+ * two or more targets, the size of each piece it gets split into must
+ * be compatible with the logical_block_size of the target processing it.
+ */
+static int validate_hardware_logical_block_alignment(struct dm_table *table)
+{
+        /*
+         * This function uses arithmetic modulo the logical_block_size
+         * (in units of 512-byte sectors).
+         */
+        unsigned short device_logical_block_size_sects =
+                table->limits.logical_block_size >> SECTOR_SHIFT;
+
+        /*
+         * Offset of the start of the next table entry, mod logical_block_size.
+         */
+        unsigned short next_target_start = 0;
+
+        /*
+         * Given an aligned bio that extends beyond the end of a
+         * target, how many sectors must the next target handle?
+         */
+        unsigned short remaining = 0;
+
+        struct dm_target *uninitialized_var(ti);
+        unsigned i = 0;
+
+        /*
+         * Check each entry in the table in turn.
+         */
+        while (i < dm_table_get_num_targets(table)) {
+                ti = dm_table_get_target(table, i++);
+
+                /*
+                 * If the remaining sectors fall entirely within this
+                 * table entry are they compatible with its logical_block_size?
+                 */
+                if (remaining < ti->len &&
+                    remaining & ((ti->limits.logical_block_size >>
+                                  SECTOR_SHIFT) - 1))
+                        break;  /* Error */
+
+                next_target_start =
+                    (unsigned short) ((next_target_start + ti->len) &
+                                      (device_logical_block_size_sects - 1));
+                remaining = next_target_start ?
+                    device_logical_block_size_sects - next_target_start : 0;
+        }
+
+        if (remaining) {
+                DMWARN("%s: table line %u (start sect %llu len %llu) "
+                       "not aligned to hardware logical block size %hu",
+                       dm_device_name(table->md), i,
+                       (unsigned long long) ti->begin,
+                       (unsigned long long) ti->len,
+                       table->limits.logical_block_size);
+                return -EINVAL;
+        }
+
+        return 0;
+}
+
 int dm_table_add_target(struct dm_table *t, const char *type,
                         sector_t start, sector_t len, char *params)
 {
@@ -823,6 +888,10 @@ int dm_table_complete(struct dm_table *t)
 
         check_for_valid_limits(&t->limits);
 
+        r = validate_hardware_logical_block_alignment(t);
+        if (r)
+                return r;
+
         /* how many indexes will the btree have ? */
         leaf_nodes = dm_div_up(t->num_targets, KEYS_PER_NODE);
         t->depth = 1 + int_log(leaf_nodes, CHILDREN_PER_NODE);