Btrfs: introduce convert_extent_bit

If I have a range where I know a certain bit is and I want to set it to another
bit the only option I have is to call set and then clear bit, which will result
in 2 tree searches.  This is inefficient, so introduce convert_extent_bit which
will go through and set the bit I want and clear the old bit I don't want.
Thanks,

Signed-off-by: Josef Bacik <josef@redhat.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 7d5e556..0ada0b7 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -894,6 +894,194 @@ search_again:
        goto again;
 }
 
+/**
+ * convert_extent - convert all bits in a given range from one bit to another
+ * @tree:      the io tree to search
+ * @start:     the start offset in bytes
+ * @end:       the end offset in bytes (inclusive)
+ * @bits:      the bits to set in this range
+ * @clear_bits:        the bits to clear in this range
+ * @mask:      the allocation mask
+ *
+ * This will go through and set bits for the given range.  If any states exist
+ * already in this range they are set with the given bit and cleared of the
+ * clear_bits.  This is only meant to be used by things that are mergeable, ie
+ * converting from say DELALLOC to DIRTY.  This is not meant to be used with
+ * boundary bits like LOCK.
+ */
+int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+                      int bits, int clear_bits, gfp_t mask)
+{
+       struct extent_state *state;
+       struct extent_state *prealloc = NULL;
+       struct rb_node *node;
+       int err = 0;
+       u64 last_start;
+       u64 last_end;
+
+again:
+       if (!prealloc && (mask & __GFP_WAIT)) {
+               prealloc = alloc_extent_state(mask);
+               if (!prealloc)
+                       return -ENOMEM;
+       }
+
+       spin_lock(&tree->lock);
+       /*
+        * this search will find all the extents that end after
+        * our range starts.
+        */
+       node = tree_search(tree, start);
+       if (!node) {
+               prealloc = alloc_extent_state_atomic(prealloc);
+               if (!prealloc)
+                       return -ENOMEM;
+               err = insert_state(tree, prealloc, start, end, &bits);
+               prealloc = NULL;
+               BUG_ON(err == -EEXIST);
+               goto out;
+       }
+       state = rb_entry(node, struct extent_state, rb_node);
+hit_next:
+       last_start = state->start;
+       last_end = state->end;
+
+       /*
+        * | ---- desired range ---- |
+        * | state |
+        *
+        * Just lock what we found and keep going
+        */
+       if (state->start == start && state->end <= end) {
+               struct rb_node *next_node;
+
+               set_state_bits(tree, state, &bits);
+               clear_state_bit(tree, state, &clear_bits, 0);
+
+               merge_state(tree, state);
+               if (last_end == (u64)-1)
+                       goto out;
+
+               start = last_end + 1;
+               next_node = rb_next(&state->rb_node);
+               if (next_node && start < end && prealloc && !need_resched()) {
+                       state = rb_entry(next_node, struct extent_state,
+                                        rb_node);
+                       if (state->start == start)
+                               goto hit_next;
+               }
+               goto search_again;
+       }
+
+       /*
+        *     | ---- desired range ---- |
+        * | state |
+        *   or
+        * | ------------- state -------------- |
+        *
+        * We need to split the extent we found, and may flip bits on
+        * second half.
+        *
+        * If the extent we found extends past our
+        * range, we just split and search again.  It'll get split
+        * again the next time though.
+        *
+        * If the extent we found is inside our range, we set the
+        * desired bit on it.
+        */
+       if (state->start < start) {
+               prealloc = alloc_extent_state_atomic(prealloc);
+               if (!prealloc)
+                       return -ENOMEM;
+               err = split_state(tree, state, prealloc, start);
+               BUG_ON(err == -EEXIST);
+               prealloc = NULL;
+               if (err)
+                       goto out;
+               if (state->end <= end) {
+                       set_state_bits(tree, state, &bits);
+                       clear_state_bit(tree, state, &clear_bits, 0);
+                       merge_state(tree, state);
+                       if (last_end == (u64)-1)
+                               goto out;
+                       start = last_end + 1;
+               }
+               goto search_again;
+       }
+       /*
+        * | ---- desired range ---- |
+        *     | state | or               | state |
+        *
+        * There's a hole, we need to insert something in it and
+        * ignore the extent we found.
+        */
+       if (state->start > start) {
+               u64 this_end;
+               if (end < last_start)
+                       this_end = end;
+               else
+                       this_end = last_start - 1;
+
+               prealloc = alloc_extent_state_atomic(prealloc);
+               if (!prealloc)
+                       return -ENOMEM;
+
+               /*
+                * Avoid to free 'prealloc' if it can be merged with
+                * the later extent.
+                */
+               err = insert_state(tree, prealloc, start, this_end,
+                                  &bits);
+               BUG_ON(err == -EEXIST);
+               if (err) {
+                       free_extent_state(prealloc);
+                       prealloc = NULL;
+                       goto out;
+               }
+               prealloc = NULL;
+               start = this_end + 1;
+               goto search_again;
+       }
+       /*
+        * | ---- desired range ---- |
+        *                        | state |
+        * We need to split the extent, and set the bit
+        * on the first half
+        */
+       if (state->start <= end && state->end > end) {
+               prealloc = alloc_extent_state_atomic(prealloc);
+               if (!prealloc)
+                       return -ENOMEM;
+
+               err = split_state(tree, state, prealloc, end + 1);
+               BUG_ON(err == -EEXIST);
+
+               set_state_bits(tree, prealloc, &bits);
+               clear_state_bit(tree, prealloc, &clear_bits, 0);
+
+               merge_state(tree, prealloc);
+               prealloc = NULL;
+               goto out;
+       }
+
+       goto search_again;
+
+out:
+       spin_unlock(&tree->lock);
+       if (prealloc)
+               free_extent_state(prealloc);
+
+       return err;
+
+search_again:
+       if (start > end)
+               goto out;
+       spin_unlock(&tree->lock);
+       if (mask & __GFP_WAIT)
+               cond_resched();
+       goto again;
+}
+
 /* wrappers around set/clear extent bit */
 int set_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
                     gfp_t mask)

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 7b2f0c3..cea445d 100644 (file)
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -214,6 +214,8 @@ int set_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
                     gfp_t mask);
 int clear_extent_dirty(struct extent_io_tree *tree, u64 start, u64 end,
                       gfp_t mask);
+int convert_extent_bit(struct extent_io_tree *tree, u64 start, u64 end,
+                      int bits, int clear_bits, gfp_t mask);
 int set_extent_delalloc(struct extent_io_tree *tree, u64 start, u64 end,
                        struct extent_state **cached_state, gfp_t mask);
 int find_first_extent_bit(struct extent_io_tree *tree, u64 start,