[PATCH v2 10/13] ext4: make ext4_es_cache_extent() support overwrite existing extents

[Zhang Yi <yi.zhang@huaweicloud.com>]

From: Zhang Yi <yi.zhang@huawei.com>

Currently, ext4_es_cache_extent() is used to load extents into the
extent status tree when reading on-disk extent blocks. But it inserts
information into the extent status tree if and only if there isn't
information about the specified range already. So it only used for the
initial loading and does not support overwrit extents.

However, there are many other places in ext4 where on-disk extents are
inserted into the extent status tree, such as in ext4_map_query_blocks().
Currently, they call ext4_es_insert_extent() to perform the insertion,
but they don't modify the extents, so ext4_es_cache_extent() would be a
more appropriate choice. However, when ext4_map_query_blocks() inserts
an extent, it may overwrite a short existing extent of the same type.
Therefore, to prepare for the replacements, we need to extend
ext4_es_cache_extent() to allow it to overwrite existing extents with
the same status. So it checks the found extents before removing and
inserting. (There is one exception, a hole in the on-disk extent but a
delayed extent in the extent status tree is allowed.)

In addition, since cached extents can be more lenient than the extents
they modify and do not involve modifying reserved blocks, it is not
necessary to ensure that the insertion operation succeeds as strictly as
in the ext4_es_insert_extent() function.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/extents_status.c | 47 ++++++++++++++++++++++++++++++++++------
 1 file changed, 40 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 818007bb613f..2643d7a31e7b 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -1014,17 +1014,23 @@ void ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 }
 
 /*
- * ext4_es_cache_extent() inserts information into the extent status
- * tree if and only if there isn't information about the range in
- * question already.
+ * ext4_es_cache_extent() inserts information into the extent status tree
+ * only if there is no existing information about the specified range or
+ * if the existing extents have the same status.
+ *
+ * Note that this interface is only used for caching on-disk extent
+ * information and cannot be used to convert existing extents in the extent
+ * status tree. To convert existing extents, use ext4_es_insert_extent()
+ * instead.
  */
 void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 			  ext4_lblk_t len, ext4_fsblk_t pblk,
 			  unsigned int status)
 {
 	struct extent_status *es;
-	struct extent_status newes;
+	struct extent_status chkes, newes;
 	ext4_lblk_t end = lblk + len - 1;
+	bool conflict = false;
 
 	if (EXT4_SB(inode->i_sb)->s_mount_state & EXT4_FC_REPLAY)
 		return;
@@ -1040,11 +1046,38 @@ void ext4_es_cache_extent(struct inode *inode, ext4_lblk_t lblk,
 	BUG_ON(end < lblk);
 
 	write_lock(&EXT4_I(inode)->i_es_lock);
-
 	es = __es_tree_search(&EXT4_I(inode)->i_es_tree.root, lblk);
-	if (!es || es->es_lblk > end)
-		__es_insert_extent(inode, &newes, NULL);
+	if (es && es->es_lblk <= end) {
+		/* Found an extent that covers the entire range. */
+		if (es->es_lblk <= lblk && es->es_lblk + es->es_len > end) {
+			if (__es_check_extent_status(es, status, &chkes))
+				conflict = true;
+			goto unlock;
+		}
+		/* Check and remove all extents in range. */
+		if (__es_remove_extent(inode, lblk, end, status, NULL,
+				       &chkes, NULL)) {
+			conflict = true;
+			goto unlock;
+		}
+	}
+	__es_insert_extent(inode, &newes, NULL);
+unlock:
 	write_unlock(&EXT4_I(inode)->i_es_lock);
+	if (!conflict)
+		return;
+	/*
+	 * A hole in the on-disk extent but a delayed extent in the extent
+	 * status tree, is allowed.
+	 */
+	if (status == EXTENT_STATUS_HOLE &&
+	    ext4_es_type(&chkes) == EXTENT_STATUS_DELAYED)
+		return;
+
+	ext4_warning_inode(inode,
+			   "ES cache extent failed: add [%d,%d,%llu,0x%x] conflict with existing [%d,%d,%llu,0x%x]\n",
+			   lblk, len, pblk, status, chkes.es_lblk, chkes.es_len,
+			   ext4_es_pblock(&chkes), ext4_es_status(&chkes));
 }
 
 /*
-- 
2.46.1