1] Add a function named ext4_split_extent_at() which splits an extent
into two extents at given logical block.
2] Add a function called ext4_split_extent() which splits an extent
into three extents.
Signed-off-by: Yongqiang Yang <xiaoqiangnk@xxxxxxxxx>
---
fs/ext4/extents.c | 200 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 200 insertions(+), 0 deletions(-)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 11f30d2..1756e0f 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2554,6 +2554,206 @@ static int ext4_ext_zeroout(struct inode *inode, struct ext4_extent *ex)
return ret;
}
+/*
+ * used by extent splitting.
+ */
+#define EXT4_EXT_MAY_ZEROOUT 0x1 /* safe to zeroout if split fails \
+ due to ENOSPC */
+#define EXT4_EXT_MARK_UNINIT1 0x2 /* mark first half uninitialized */
+#define EXT4_EXT_MARK_UNINIT2 0x4 /* mark second half uninitialized */
+
+/*
+ * ext4_split_extent_at() splits an extent at given block.
+ *
+ * @handle: the journal handle
+ * @inode: the file inode
+ * @path: the path to the extent
+ * @split: the logical block where the extent is splitted.
+ * @split_flags: indicates if the extent could be zeroout if split fails, and
+ * the states(init or uninit) of new extents.
+ * @flags: flags used to insert new extent to extent tree.
+ *
+ *
+ * Splits extent [a, b] into two extents [a, @split) and [@split, b], states
+ * of which are deterimined by split_flag.
+ *
+ * There are two cases:
+ * a> the extent are splitted into two extent.
+ * b> split is not needed, and just mark the extent.
+ *
+ * return 0 on success.
+ */
+static int ext4_split_extent_at(handle_t *handle,
+ struct inode *inode,
+ struct ext4_ext_path *path,
+ ext4_lblk_t split,
+ int split_flag,
+ int flags)
+{
+ ext4_fsblk_t newblock;
+ ext4_lblk_t ee_block;
+ struct ext4_extent_header *eh;
+ struct ext4_extent *ex, newex, orig_ex;
+ struct ext4_extent *ex2 = NULL;
+ unsigned int ee_len, depth;
+ int err = 0;
+
+ ext_debug("ext4_split_extents_at: inode %lu, logical"
+ "block %llu\n", inode->i_ino, (unsigned long long)split);
+
+ ext4_ext_show_leaf(inode, path);
+
+ depth = ext_depth(inode);
+ eh = path[depth].p_hdr;
+ ex = path[depth].p_ext;
+ ee_block = le32_to_cpu(ex->ee_block);
+ ee_len = ext4_ext_get_actual_len(ex);
+ newblock = split - ee_block + ext4_ext_pblock(ex);
+
+ BUG_ON(split < ee_block || split >= (ee_block + ee_len));
+
+ err = ext4_ext_get_access(handle, inode, path + depth);
+ if (err)
+ goto out;
+
+ if (split == ee_block) {
+ /*
+ * case b: block @split is the block that the extent begins with
+ * then we just change the state of the extent, and splitting
+ * is not needed.
+ */
+ if (split_flag & EXT4_EXT_MARK_UNINIT2)
+ ext4_ext_mark_uninitialized(ex);
+ else
+ ext4_ext_mark_initialized(ex);
+
+ if (!(flags & EXT4_GET_BLOCKS_PRE_IO))
+ ext4_ext_try_to_merge(inode, path, ex);
+
+ err = ext4_ext_dirty(handle, inode, path + depth);
+ goto out;
+ }
+
+ /* case a */
+ orig_ex.ee_block = ex->ee_block;
+ orig_ex.ee_len = ex->ee_len;
+ ext4_ext_store_pblock(&orig_ex, ext4_ext_pblock(ex));
+
+ ex->ee_len = cpu_to_le16(split - ee_block);
+ if (split_flag & EXT4_EXT_MARK_UNINIT1)
+ ext4_ext_mark_uninitialized(ex);
+
+ /*
+ * path may lead to new leaf, not to original leaf any more
+ * after ext4_ext_insert_extent() returns,
+ */
+ err = ext4_ext_dirty(handle, inode, path + depth);
+ if (err)
+ goto fix_extent_len;
+
+ ex2 = &newex;
+ ex2->ee_block = cpu_to_le32(split);
+ ex2->ee_len = cpu_to_le16(ee_len - (split - ee_block));
+ ext4_ext_store_pblock(ex2, newblock);
+ if (split_flag & EXT4_EXT_MARK_UNINIT2)
+ ext4_ext_mark_uninitialized(ex2);
+
+ err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
+ if (err == -ENOSPC && (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
+
+ err = ext4_ext_zeroout(inode, &orig_ex);
+ if (err)
+ goto fix_extent_len;
+ /* update the extent length and mark as initialized */
+ ex->ee_block = orig_ex.ee_block;
+ ex->ee_len = orig_ex.ee_len;
+ ext4_ext_mark_initialized(ex);
+ ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
+ err = ext4_ext_dirty(handle, inode, path + depth);
+ goto out;
+ } else if (err)
+ goto fix_extent_len;
+
+out:
+ ext4_ext_show_leaf(inode, path);
+ return err;
+
+fix_extent_len:
+ ex->ee_block = orig_ex.ee_block;
+ ex->ee_len = orig_ex.ee_len;
+ ext4_ext_store_pblock(ex, ext4_ext_pblock(&orig_ex));
+ ext4_ext_dirty(handle, inode, path + depth);
+ return err;
+}
+
+/*
+ * ext4_split_extents() splits an extent and mark extent which is covered
+ * by @map as split_flags indicates
+ *
+ * It may result in splitting the extent into multiple extents (upto three)
+ * There are three possibilities:
+ * a> There is no split required
+ * b> Splits in two extents: Split is happening at either end of the extent
+ * c> Splits in three extents: Somone is splitting in middle of the extent
+ *
+ */
+static int ext4_split_extent(handle_t *handle,
+ struct inode *inode,
+ struct ext4_ext_path *path,
+ struct ext4_map_blocks *map,
+ int split_flag,
+ int flags)
+{
+ ext4_lblk_t ee_block;
+ struct ext4_extent *ex;
+ unsigned int ee_len, depth;
+ int err = 0;
+ int uninitialized;
+ int split_flag1, flags1;
+
+ depth = ext_depth(inode);
+ ex = path[depth].p_ext;
+ ee_block = le32_to_cpu(ex->ee_block);
+ ee_len = ext4_ext_get_actual_len(ex);
+ uninitialized = ext4_ext_is_uninitialized(ex);
+
+ if (map->m_lblk + map->m_len < ee_block + ee_len) {
+ split_flag1 = 0;
+ split_flag1 |= split_flag & EXT4_EXT_MAY_ZEROOUT ?
+ EXT4_EXT_MAY_ZEROOUT : 0;
+ flags1 = flags;
+ flags1 |= EXT4_GET_BLOCKS_PRE_IO;
+ if (uninitialized)
+ split_flag1 |= EXT4_EXT_MARK_UNINIT1 |
+ EXT4_EXT_MARK_UNINIT2;
+ err = ext4_split_extent_at(handle, inode, path,
+ map->m_lblk + map->m_len, split_flag1, flags1);
+ }
+
+ ext4_ext_drop_refs(path);
+ path = ext4_ext_find_extent(inode, map->m_lblk, path);
+ if (IS_ERR(path))
+ return PTR_ERR(path);
+
+ if (map->m_lblk >= ee_block) {
+ split_flag1 = 0;
+ split_flag1 |= split_flag & EXT4_EXT_MAY_ZEROOUT ?
+ EXT4_EXT_MAY_ZEROOUT : 0;
+ if (uninitialized)
+ split_flag1 |= EXT4_EXT_MARK_UNINIT1;
+ if (split_flag & EXT4_EXT_MARK_UNINIT2)
+ split_flag1 |= EXT4_EXT_MARK_UNINIT2;
+ err = ext4_split_extent_at(handle, inode, path,
+ map->m_lblk, split_flag1, flags);
+ if (err)
+ goto out;
+ }
+
+ ext4_ext_show_leaf(inode, path);
+out:
+ return err ? err : map->m_len;
+}
+
#define EXT4_EXT_ZERO_LEN 7
/*
* This function is called by ext4_ext_map_blocks() if someone tries to write
--
1.7.4.4
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