1 files changed, 78 insertions, 43 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 6ae118d6e193..d52d4adc440b 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -505,21 +505,30 @@ static unsigned int lcm(unsigned int a, unsigned int b)
 
 /**
  * blk_stack_limits - adjust queue_limits for stacked devices
- * @t:  the stacking driver limits (top)
- * @b:  the underlying queue limits (bottom)
+ * @t:  the stacking driver limits (top device)
+ * @b:  the underlying queue limits (bottom, component device)
  * @offset:  offset to beginning of data within component device
  *
  * Description:
- *    Merges two queue_limit structs.  Returns 0 if alignment didn't
- *    change.  Returns -1 if adding the bottom device caused
- *    misalignment.
+ *    This function is used by stacking drivers like MD and DM to ensure
+ *    that all component devices have compatible block sizes and
+ *    alignments.  The stacking driver must provide a queue_limits
+ *    struct (top) and then iteratively call the stacking function for
+ *    all component (bottom) devices.  The stacking function will
+ *    attempt to combine the values and ensure proper alignment.
+ *
+ *    Returns 0 if the top and bottom queue_limits are compatible.  The
+ *    top device's block sizes and alignment offsets may be adjusted to
+ *    ensure alignment with the bottom device. If no compatible sizes
+ *    and alignments exist, -1 is returned and the resulting top
+ *    queue_limits will have the misaligned flag set to indicate that
+ *    the alignment_offset is undefined.
  */
 int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
                      sector_t offset)
 {
-        int ret;
-
-        ret = 0;
+        sector_t alignment;
+        unsigned int top, bottom;
 
         t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
         t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
@@ -537,6 +546,22 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
         t->max_segment_size = min_not_zero(t->max_segment_size,
                                            b->max_segment_size);
 
+        alignment = queue_limit_alignment_offset(b, offset);
+
+        /* Bottom device has different alignment.  Check that it is
+         * compatible with the current top alignment.
+         */
+        if (t->alignment_offset != alignment) {
+
+                top = max(t->physical_block_size, t->io_min)
+                        + t->alignment_offset;
+                bottom = max(b->physical_block_size, b->io_min) + alignment;
+
+                /* Verify that top and bottom intervals line up */
+                if (max(top, bottom) & (min(top, bottom) - 1))
+                        t->misaligned = 1;
+        }
+
         t->logical_block_size = max(t->logical_block_size,
                                     b->logical_block_size);
 
@@ -544,54 +569,64 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
                                      b->physical_block_size);
 
         t->io_min = max(t->io_min, b->io_min);
+        t->io_opt = lcm(t->io_opt, b->io_opt);
+
         t->no_cluster |= b->no_cluster;
         t->discard_zeroes_data &= b->discard_zeroes_data;
 
-        /* Bottom device offset aligned? */
-        if (offset &&
-            (offset & (b->physical_block_size - 1)) != b->alignment_offset) {
+        /* Physical block size a multiple of the logical block size? */
+        if (t->physical_block_size & (t->logical_block_size - 1)) {
+                t->physical_block_size = t->logical_block_size;
                 t->misaligned = 1;
-                ret = -1;
         }
 
-        /*
-         * Temporarily disable discard granularity. It's currently buggy
-         * since we default to 0 for discard_granularity, hence this
-         * "failure" will always trigger for non-zero offsets.
-         */
-#if 0
-        if (offset &&
-            (offset & (b->discard_granularity - 1)) != b->discard_alignment) {
-                t->discard_misaligned = 1;
-                ret = -1;
+        /* Minimum I/O a multiple of the physical block size? */
+        if (t->io_min & (t->physical_block_size - 1)) {
+                t->io_min = t->physical_block_size;
+                t->misaligned = 1;
         }
-#endif
-
-        /* If top has no alignment offset, inherit from bottom */
-        if (!t->alignment_offset)
-                t->alignment_offset =
-                        b->alignment_offset & (b->physical_block_size - 1);
 
-        if (!t->discard_alignment)
-                t->discard_alignment =
-                        b->discard_alignment & (b->discard_granularity - 1);
-
-        /* Top device aligned on logical block boundary? */
-        if (t->alignment_offset & (t->logical_block_size - 1)) {
+        /* Optimal I/O a multiple of the physical block size? */
+        if (t->io_opt & (t->physical_block_size - 1)) {
+                t->io_opt = 0;
                 t->misaligned = 1;
-                ret = -1;
         }
 
-        /* Find lcm() of optimal I/O size and granularity */
-        t->io_opt = lcm(t->io_opt, b->io_opt);
-        t->discard_granularity = lcm(t->discard_granularity,
-                                     b->discard_granularity);
+        /* Find lowest common alignment_offset */
+        t->alignment_offset = lcm(t->alignment_offset, alignment)
+                & (max(t->physical_block_size, t->io_min) - 1);
 
-        /* Verify that optimal I/O size is a multiple of io_min */
-        if (t->io_min && t->io_opt % t->io_min)
-                ret = -1;
+        /* Verify that new alignment_offset is on a logical block boundary */
+        if (t->alignment_offset & (t->logical_block_size - 1))
+                t->misaligned = 1;
+
+        /* Discard alignment and granularity */
+        if (b->discard_granularity) {
+                unsigned int granularity = b->discard_granularity;
+                offset &= granularity - 1;
+
+                alignment = (granularity + b->discard_alignment - offset)
+                        & (granularity - 1);
+
+                if (t->discard_granularity != 0 &&
+                    t->discard_alignment != alignment) {
+                        top = t->discard_granularity + t->discard_alignment;
+                        bottom = b->discard_granularity + alignment;
+
+                        /* Verify that top and bottom intervals line up */
+                        if (max(top, bottom) & (min(top, bottom) - 1))
+                                t->discard_misaligned = 1;
+                }
+
+                t->max_discard_sectors = min_not_zero(t->max_discard_sectors,
+                                                      b->max_discard_sectors);
+                t->discard_granularity = max(t->discard_granularity,
+                                             b->discard_granularity);
+                t->discard_alignment = lcm(t->discard_alignment, alignment) &
+                        (t->discard_granularity - 1);
+        }
 
-        return ret;
+        return t->misaligned ? -1 : 0;
 }
 EXPORT_SYMBOL(blk_stack_limits);