btrfs-progs: convert: simplify insert_temp_dev_item() and insert_temp_chunk_item()

These functions require parameters @slot and @itemoff to record where the
next item should land.

But this is overkilled, as after inserting an item, the temporary extent
buffer will have its header nritems and the item pointer updated.

We can use that header nritems and item pointer to get where the next
item should land.

This removes the external counter to record @slot and @itemoff.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: adam900710

convert/common.c

@@ -292,14 +292,15 @@ static int setup_temp_root_tree(int fd, struct btrfs_mkfs_config *cfg,
 }
 
 static int insert_temp_dev_item(int fd, struct extent_buffer *buf,
-				struct btrfs_mkfs_config *cfg,
-				int *slot, u32 *itemoff)
+				struct btrfs_mkfs_config *cfg)
 {
 	struct btrfs_disk_key disk_key;
 	struct btrfs_dev_item *dev_item;
 	unsigned char dev_uuid[BTRFS_UUID_SIZE];
 	unsigned char fsid[BTRFS_FSID_SIZE];
 	struct btrfs_super_block super;
+	u32 slot = btrfs_header_nritems(buf);
+	u32 itemoff = get_item_offset(buf, cfg);
 	int ret;
 
 	ret = pread(fd, &super, BTRFS_SUPER_INFO_SIZE, cfg->super_bytenr);
@@ -308,17 +309,17 @@ static int insert_temp_dev_item(int fd, struct extent_buffer *buf,
 		goto out;
 	}
 
-	btrfs_set_header_nritems(buf, *slot + 1);
-	(*itemoff) -= sizeof(*dev_item);
+	btrfs_set_header_nritems(buf, slot + 1);
+	itemoff -= sizeof(*dev_item);
 	/* setup device item 1, 0 is for replace case */
 	btrfs_set_disk_key_type(&disk_key, BTRFS_DEV_ITEM_KEY);
 	btrfs_set_disk_key_objectid(&disk_key, BTRFS_DEV_ITEMS_OBJECTID);
 	btrfs_set_disk_key_offset(&disk_key, 1);
-	btrfs_set_item_key(buf, &disk_key, *slot);
-	btrfs_set_item_offset(buf, *slot, *itemoff);
-	btrfs_set_item_size(buf, *slot, sizeof(*dev_item));
+	btrfs_set_item_key(buf, &disk_key, slot);
+	btrfs_set_item_offset(buf, slot, itemoff);
+	btrfs_set_item_size(buf, slot, sizeof(*dev_item));
 
-	dev_item = btrfs_item_ptr(buf, *slot, struct btrfs_dev_item);
+	dev_item = btrfs_item_ptr(buf, slot, struct btrfs_dev_item);
 	/* Generate device uuid */
 	uuid_generate(dev_uuid);
 	write_extent_buffer(buf, dev_uuid,
@@ -346,19 +347,19 @@ static int insert_temp_dev_item(int fd, struct extent_buffer *buf,
 	read_extent_buffer(buf, &super.dev_item, (unsigned long)dev_item,
 			   sizeof(*dev_item));
 	ret = write_temp_super(fd, &super, cfg->super_bytenr);
-	(*slot)++;
 out:
 	return ret;
 }
 
 static int insert_temp_chunk_item(int fd, struct extent_buffer *buf,
 				  struct btrfs_mkfs_config *cfg,
-				  int *slot, u32 *itemoff, u64 start, u64 len,
-				  u64 type)
+				  u64 start, u64 len, u64 type)
 {
 	struct btrfs_chunk *chunk;
 	struct btrfs_disk_key disk_key;
 	struct btrfs_super_block sb;
+	u32 slot = btrfs_header_nritems(buf);
+	u32 itemoff = get_item_offset(buf, cfg);
 	int ret = 0;
 
 	ret = pread(fd, &sb, BTRFS_SUPER_INFO_SIZE, cfg->super_bytenr);
@@ -367,16 +368,16 @@ static int insert_temp_chunk_item(int fd, struct extent_buffer *buf,
 		return ret;
 	}
 
-	btrfs_set_header_nritems(buf, *slot + 1);
-	(*itemoff) -= btrfs_chunk_item_size(1);
+	btrfs_set_header_nritems(buf, slot + 1);
+	itemoff -= btrfs_chunk_item_size(1);
 	btrfs_set_disk_key_type(&disk_key, BTRFS_CHUNK_ITEM_KEY);
 	btrfs_set_disk_key_objectid(&disk_key, BTRFS_FIRST_CHUNK_TREE_OBJECTID);
 	btrfs_set_disk_key_offset(&disk_key, start);
-	btrfs_set_item_key(buf, &disk_key, *slot);
-	btrfs_set_item_offset(buf, *slot, *itemoff);
-	btrfs_set_item_size(buf, *slot, btrfs_chunk_item_size(1));
+	btrfs_set_item_key(buf, &disk_key, slot);
+	btrfs_set_item_offset(buf, slot, itemoff);
+	btrfs_set_item_size(buf, slot, btrfs_chunk_item_size(1));
 
-	chunk = btrfs_item_ptr(buf, *slot, struct btrfs_chunk);
+	chunk = btrfs_item_ptr(buf, slot, struct btrfs_chunk);
 	btrfs_set_chunk_length(buf, chunk, len);
 	btrfs_set_chunk_owner(buf, chunk, BTRFS_EXTENT_TREE_OBJECTID);
 	btrfs_set_chunk_stripe_len(buf, chunk, BTRFS_STRIPE_LEN);
@@ -392,7 +393,6 @@ static int insert_temp_chunk_item(int fd, struct extent_buffer *buf,
 	write_extent_buffer(buf, sb.dev_item.uuid,
 			    (unsigned long)btrfs_stripe_dev_uuid_nr(chunk, 0),
 			    BTRFS_UUID_SIZE);
-	(*slot)++;
 
 	/*
 	 * If it's system chunk, also copy it to super block.
@@ -422,8 +422,6 @@ static int setup_temp_chunk_tree(int fd, struct btrfs_mkfs_config *cfg,
 				 u64 chunk_bytenr)
 {
 	struct extent_buffer *buf = NULL;
-	u32 itemoff = cfg->leaf_data_size;
-	int slot = 0;
 	int ret;
 
 	/* Must ensure SYS chunk starts before META chunk */
@@ -440,17 +438,15 @@ static int setup_temp_chunk_tree(int fd, struct btrfs_mkfs_config *cfg,
 	if (ret < 0)
 		goto out;
 
-	ret = insert_temp_dev_item(fd, buf, cfg, &slot, &itemoff);
+	ret = insert_temp_dev_item(fd, buf, cfg);
 	if (ret < 0)
 		goto out;
-	ret = insert_temp_chunk_item(fd, buf, cfg, &slot, &itemoff,
-				     sys_chunk_start,
+	ret = insert_temp_chunk_item(fd, buf, cfg, sys_chunk_start,
 				     BTRFS_MKFS_SYSTEM_GROUP_SIZE,
 				     BTRFS_BLOCK_GROUP_SYSTEM);
 	if (ret < 0)
 		goto out;
-	ret = insert_temp_chunk_item(fd, buf, cfg, &slot, &itemoff,
-				     meta_chunk_start,
+	ret = insert_temp_chunk_item(fd, buf, cfg, meta_chunk_start,
 				     BTRFS_CONVERT_META_GROUP_SIZE,
 				     BTRFS_BLOCK_GROUP_METADATA);
 	if (ret < 0)