ref: 45a1867fb54cf994a51d897ee7eb83f31d72f3fc
parent: dbcf9937ca2a64604133b2c38ecea906c90f7f2c
author: Kaho Ng <ngkaho1234@gmail.com>
date: Tue May 31 20:06:46 EDT 2016
ext4_extent: add comments to truncate routines
--- a/src/ext4_extent.c
+++ b/src/ext4_extent.c
@@ -1215,6 +1215,13 @@
to_le32(path[i].index->first_block), leaf, 1);
ext4_ext_free_blocks(inode_ref, leaf, 1, 0);
+ /*
+ * We may need to correct the paths after the first extents/indexes in
+ * a node being modified.
+ *
+ * We do not need to consider whether there's any extents presenting or
+ * not, as garbage will be cleared soon.
+ */
while (i > 0) {if (path[i].index != EXT_FIRST_INDEX(path[i].header))
break;
@@ -1253,6 +1260,12 @@
new_start = start = to_le32(ex->first_block);
len = ext4_ext_get_actual_len(ex);
newblock = ext4_ext_pblock(ex);
+ /*
+ * The 1st case:
+ * The position that we start truncation is inside the range of an
+ * extent. Here we should calculate the new length of that extent and
+ * may start the removal from the next extent.
+ */
if (start < from) {len -= from - start;
new_len = from - start;
@@ -1259,6 +1272,12 @@
start = from;
start_ex++;
} else {+ /*
+ * The second case:
+ * The last block to be truncated is inside the range of an
+ * extent. We need to calculate the new length and the new
+ * start of the extent.
+ */
if (start + len - 1 > to) {new_len = start + len - 1 - to;
len -= new_len;
@@ -1269,7 +1288,15 @@
}
ext4_ext_remove_blocks(inode_ref, ex, start, start + len - 1);
+ /*
+ * Set the first block of the extent if it is presented.
+ */
ex->first_block = to_le32(new_start);
+
+ /*
+ * If the new length of the current extent we are working on is
+ * zero, remove it.
+ */
if (!new_len)
new_entries--;
else {@@ -1286,6 +1313,9 @@
if (ex2 == NULL)
ex2 = ex;
+ /*
+ * Move any remaining extents to the starting position of the node.
+ */
if (ex2 <= EXT_LAST_EXTENT(eh))
memmove(start_ex, ex2, (EXT_LAST_EXTENT(eh) - ex2 + 1) *
sizeof(struct ext4_extent));
@@ -1292,6 +1322,12 @@
eh->entries_count = to_le16(new_entries);
ext4_ext_dirty(inode_ref, path + depth);
+
+ /*
+ * If the extent pointer is pointed to the first extent of the node, and
+ * there's still extents presenting, we may need to correct the indexes
+ * of the paths.
+ */
if (path[depth].extent == EXT_FIRST_EXTENT(eh) && eh->entries_count) {err = ext4_ext_correct_indexes(inode_ref, path);
if (err != EOK)
@@ -1308,6 +1344,9 @@
return err;
}
+/*
+ * Check if there's more to remove at a specific level.
+ */
static bool ext4_ext_more_to_rm(struct ext4_extent_path *path, ext4_lblk_t to)
{if (!to_le16(path->header->entries_count))
@@ -1427,6 +1466,9 @@
i++;
} else { if (i > 0) {+ /*
+ * Garbage entries will finally be cleared here.
+ */
if (!eh->entries_count)
ret = ext4_ext_remove_idx(inode_ref,
path, i - 1);