[PATCH v2] btrfs-progs: print-tree: Enehance uuid item print

[Qu Wenruo <wqu@suse.com>]

For key type BTRFS_UUID_KEY_SUBVOL or BTRFS_UUID_KEY_RECEIVED_SUBVOL the
key objectid and key offset is just half of the UUID.

However we just print the key as %llu, which is converted from little
endian, not byte order for UUID, nor the traditional 36 bytes human
readable uuid format.

Although true engineer can easily handle it by convert it in their
brain, but to make it easier for search, output the result UUID using
the 36 chars format.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
Inspired by UUID related work from Misono-san.
v2:
  Use explicit btrfs_key_to_uuid() function to do the convert, and add
  more comment why we should do that. Suggested by Nikolay.
---
 print-tree.c | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/print-tree.c b/print-tree.c
index 3c585e31f1fc..ab6f6c392519 100644
--- a/print-tree.c
+++ b/print-tree.c
@@ -803,14 +803,42 @@ void btrfs_print_key(struct btrfs_disk_key *disk_key)
 	}
 }
 
-static void print_uuid_item(struct extent_buffer *l, unsigned long offset,
-			    u32 item_size)
+static void btrfs_key_to_uuid(struct btrfs_key *key, u8 *uuid)
 {
+	/*
+	 * UUID we use is in byte order, which means:
+	 *          0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
+	 * UUID:0x 12 34 56-78 90-ab cd-ef 12-34 56 78 90 ab cd ef
+	 *
+	 * And we store them as is in btrfs_*disk*_key:
+	 *
+	 *         Low bit        High bit|Low bit        High bit
+	 * LE64:0x 12 34 56-78 90-ab cd-ef|12-34 56 78 90 ab cd ef
+	 *             key.objectid       |     key.offset
+	 *
+	 * So here we just need to convert from native endian to LE to
+	 * get the byte order UUID.
+	 */
+	put_unaligned_le64(key->objectid, uuid);
+	put_unaligned_le64(key->offset, uuid + sizeof(u64));
+}
+
+static void print_uuid_item(struct extent_buffer *l, int slot,
+			    unsigned long offset, u32 item_size)
+{
+	struct btrfs_key key;
+	char uuid_str[BTRFS_UUID_UNPARSED_SIZE];
+	u8 uuid[BTRFS_UUID_SIZE];
+
+	btrfs_item_key_to_cpu(l, &key, slot);
+	btrfs_key_to_uuid(&key, uuid);
+	uuid_unparse(uuid, uuid_str);
 	if (item_size & (sizeof(u64) - 1)) {
 		printf("btrfs: uuid item with illegal size %lu!\n",
 		       (unsigned long)item_size);
 		return;
 	}
+	printf("\t\tuuid %s\n", uuid_str);
 	while (item_size) {
 		__le64 subvol_id;
 
@@ -1297,7 +1325,7 @@ void btrfs_print_leaf(struct btrfs_root *root, struct extent_buffer *eb)
 			break;
 		case BTRFS_UUID_KEY_SUBVOL:
 		case BTRFS_UUID_KEY_RECEIVED_SUBVOL:
-			print_uuid_item(eb, btrfs_item_ptr_offset(eb, i),
+			print_uuid_item(eb, i, btrfs_item_ptr_offset(eb, i),
 					btrfs_item_size_nr(eb, i));
 			break;
 		case BTRFS_STRING_ITEM_KEY: {
-- 
2.14.3