On 31.10.2017 10:28, Qu Wenruo wrote:
> 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@xxxxxxxx>
> ---
> 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:
"byte order" term per-se doesn't really say anything about how bytes are
stored, we either have little endian or big endian. So this sentence
needs to be more explicit "BTRFS always represents uuid in little endian"
> + * 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:
This could be "BTRFS' on-disk format also uses little-endian so the
in-memory uuid is stored on-disk without any change to endiannes"
> + *
> + * 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: {
>
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