[PATCH 3/7] btrfs: defrag: introduce a new helper to collect target file extents

[Qu Wenruo <wqu@suse.com>]

Introduce a new helper, defrag_collect_targets(), to collect all
possible targets to be defraged.

This function will not consider things like max_sectors_to_defrag, thus
caller should be responsible to ensure we don't exceed the limit.

This function will be the first stage of later defrag rework.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ioctl.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index ba69991bca10..1e57293a05f2 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1375,6 +1375,117 @@ static int cluster_pages_for_defrag(struct inode *inode,
 
 }
 
+struct defrag_target_range {
+	struct list_head list;
+	u64 start;
+	u64 len;
+};
+
+/*
+ * Helper to collect all valid target extents.
+ *
+ * @start:	   The file offset to lookup
+ * @len:	   The length to lookup
+ * @extent_thresh: File extent size threshold, any extent size >= this value
+ * 		   will be ignored
+ * @newer_than:    Only defrag extents newer than this value
+ * @do_compress:   Whether the defrag is doing compression
+ * 		   If true, @extent_thresh will be ignored and all regular
+ * 		   file extents meeting @newer_than will be targets.
+ * @target_list:   The list of targets file extents
+ */
+static int defrag_collect_targets(struct btrfs_inode *inode,
+				  u64 start, u64 len, u32 extent_thresh,
+				  u64 newer_than, bool do_compress,
+				  struct list_head *target_list)
+{
+	u64 cur = start;
+	int ret = 0;
+
+	while (cur < start + len) {
+		struct extent_map *em;
+		struct defrag_target_range *new;
+		bool next_mergeable = true;
+		u64 range_len;
+
+		em = defrag_lookup_extent(&inode->vfs_inode, cur);
+		if (!em)
+			break;
+
+		/* Skip hole/inline/preallocated extents */
+		if (em->block_start >= EXTENT_MAP_LAST_BYTE ||
+		    test_bit(EXTENT_FLAG_PREALLOC, &em->flags))
+			goto next;
+
+		/* Skip older extent */
+		if (em->generation < newer_than)
+			goto next;
+
+		/*
+		 * For do_compress case, we want to compress all valid file
+		 * extents, thus no @extent_thresh or mergable check.
+		 */
+		if (do_compress)
+			goto add;
+
+		/* Skip too large extent */
+		if (em->len >= extent_thresh)
+			goto next;
+
+		next_mergeable = defrag_check_next_extent(&inode->vfs_inode, em);
+		if (!next_mergeable) {
+			struct defrag_target_range *last;
+
+			/* Empty target list, no way to merge with last entry */
+			if (list_empty(target_list))
+				goto next;
+			last = list_entry(target_list->prev,
+					struct defrag_target_range, list);
+			/* Not mergable with last entry */
+			if (last->start + last->len != cur)
+				goto next;
+
+			/* Mergable, fall throught to add it to @target_list. */
+		}
+
+add:
+		range_len = min(extent_map_end(em), start + len) - cur;
+		/*
+		 * This one is a good target, check if it can be merged into
+		 * last range of the target list
+		 */
+		if (!list_empty(target_list)) {
+			struct defrag_target_range *last;
+
+			last = list_entry(target_list->prev,
+					struct defrag_target_range, list);
+			ASSERT(last->start + last->len <= cur);
+			if (last->start + last->len == cur) {
+				/* Mergable, enlarge the last entry */
+				last->len += range_len;
+				goto next;
+			}
+			/* Fall through to allocate a new entry */
+		}
+
+		/* Allocate new defrag_target_range */
+		new = kmalloc(sizeof(*new), GFP_NOFS);
+		if (!new) {
+			ret = -ENOMEM;
+			free_extent_map(em);
+			break;
+		}
+		new->start = cur;
+		new->len = range_len;
+		list_add_tail(&new->list, target_list);
+
+next:
+		cur = extent_map_end(em);
+		free_extent_map(em);
+	}
+	return ret;
+}
+
 /*
  * Btrfs entrace for defrag.
  *
-- 
2.31.1