btrfs: Implement find_first_clear_extent_bit

This function is very similar to find_first_extent_bit except that it
locates the first contiguous span of space which does not have bits set.
It's intended use is in the freespace trimming code.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index ff1f7b4..828708f 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1542,6 +1542,79 @@ out:
        return ret;
 }
 
+/**
+ * find_first_clear_extent_bit - finds the first range that has @bits not set
+ * and that starts after @start
+ *
+ * @tree - the tree to search
+ * @start - the offset at/after which the found extent should start
+ * @start_ret - records the beginning of the range
+ * @end_ret - records the end of the range (inclusive)
+ * @bits - the set of bits which must be unset
+ *
+ * Since unallocated range is also considered one which doesn't have the bits
+ * set it's possible that @end_ret contains -1, this happens in case the range
+ * spans (last_range_end, end of device]. In this case it's up to the caller to
+ * trim @end_ret to the appropriate size.
+ */
+void find_first_clear_extent_bit(struct extent_io_tree *tree, u64 start,
+                                u64 *start_ret, u64 *end_ret, unsigned bits)
+{
+       struct extent_state *state;
+       struct rb_node *node, *prev = NULL, *next;
+
+       spin_lock(&tree->lock);
+
+       /* Find first extent with bits cleared */
+       while (1) {
+               node = __etree_search(tree, start, &next, &prev, NULL, NULL);
+               if (!node) {
+                       node = next;
+                       if (!node) {
+                               /*
+                                * We are past the last allocated chunk,
+                                * set start at the end of the last extent. The
+                                * device alloc tree should never be empty so
+                                * prev is always set.
+                                */
+                               ASSERT(prev);
+                               state = rb_entry(prev, struct extent_state, rb_node);
+                               *start_ret = state->end + 1;
+                               *end_ret = -1;
+                               goto out;
+                       }
+               }
+               state = rb_entry(node, struct extent_state, rb_node);
+               if (in_range(start, state->start, state->end - state->start + 1) &&
+                       (state->state & bits)) {
+                       start = state->end + 1;
+               } else {
+                       *start_ret = start;
+                       break;
+               }
+       }
+
+       /*
+        * Find the longest stretch from start until an entry which has the
+        * bits set
+        */
+       while (1) {
+               state = rb_entry(node, struct extent_state, rb_node);
+               if (state->end >= start && !(state->state & bits)) {
+                       *end_ret = state->end;
+               } else {
+                       *end_ret = state->start - 1;
+                       break;
+               }
+
+               node = rb_next(node);
+               if (!node)
+                       break;
+       }
+out:
+       spin_unlock(&tree->lock);
+}
+
 /*
  * find a contiguous range of bytes in the file marked as delalloc, not
  * more than 'max_bytes'.  start and end are used to return the range,

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 1680832..f7ca151 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -403,6 +403,8 @@ static inline int set_extent_uptodate(struct extent_io_tree *tree, u64 start,
 int find_first_extent_bit(struct extent_io_tree *tree, u64 start,
                          u64 *start_ret, u64 *end_ret, unsigned bits,
                          struct extent_state **cached_state);
+void find_first_clear_extent_bit(struct extent_io_tree *tree, u64 start,
+                                u64 *start_ret, u64 *end_ret, unsigned bits);
 int extent_invalidatepage(struct extent_io_tree *tree,
                          struct page *page, unsigned long offset);
 int extent_write_full_page(struct page *page, struct writeback_control *wbc);