On Wed, Apr 22 2009 at 9:25am -0400,
Alasdair G Kergon <agk@xxxxxxxxxx> wrote:
> I've tried to make this easier to understand.
> Please check I've not broken something in the process...
Looks good, I especially like what you did with the revised DM_WARN().
But there were some minor compiler warnings:
drivers/md/dm-table.c: In function ‘validate_hardsect_alignment’:
drivers/md/dm-table.c:763: warning: suggest parentheses around + or - in operand of &
drivers/md/dm-table.c: In function ‘dm_table_complete’:
drivers/md/dm-table.c:749: warning: ‘ti’ may be used uninitialized in this function
I fixed these warnings in the following revised patch. I then fixed
this checkpatch warning (which resulted in somewhat uglier code):
WARNING: line over 80 characters
#74: FILE: drivers/md/dm-table.c:763:
+ remaining & ((ti->limits.hardsect_size >> SECTOR_SHIFT) - 1))
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 429b50b..73f0438 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -693,6 +693,71 @@ 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 hardsect_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 hardsect_size of the target processing it.
+ */
+static int validate_hardsect_alignment(struct dm_table *table)
+{
+ /*
+ * This function uses arithmetic modulo the hardsect_size
+ * (in units of 512-byte sectors).
+ */
+ unsigned short device_hardsect_size_sects =
+ table->limits.hardsect_size >> SECTOR_SHIFT;
+
+ /*
+ * Offset of the start of the next table entry, mod hardsect_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 *ti = NULL;
+ 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 hardsect_size?
+ */
+ if (remaining < ti->len &&
+ remaining & ((ti->limits.hardsect_size >>
+ SECTOR_SHIFT) - 1))
+ break; /* Error */
+
+ next_target_start =
+ (unsigned short) ((next_target_start + ti->len) &
+ (device_hardsect_size_sects - 1));
+ remaining = next_target_start ?
+ device_hardsect_size_sects - next_target_start : 0;
+ }
+
+ if (remaining) {
+ DMWARN("%s: table line %u (start sect %llu len %llu) "
+ "not aligned to hardware sector size %hu",
+ dm_device_name(table->md), i,
+ (unsigned long long) ti->begin,
+ (unsigned long long) ti->len,
+ table->limits.hardsect_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)
{
@@ -792,6 +857,10 @@ int dm_table_complete(struct dm_table *t)
check_for_valid_limits(&t->limits);
+ r = validate_hardsect_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);
--
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