On 31.10.2017 09:15, Nikolay Borisov wrote:
>
>
> On 31.10.2017 06:03, Qu Wenruo wrote:
>> For key type BTRFS_UUID_KEY_SUBVOL or BTRFS_UUID_KEY_RECEIVED_SUBVOL the
>> key objectid and key offset are 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 convert it in their brain, but to
>> make it easier for search, output the result UUID using the 36 chars format.
>>
>> Cc: Misono Tomohiro <misono.tomohiro@xxxxxxxxxxxxxx>
>> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
>> ---
>> Inspired by UUID related work from Misono.
>> ---
>> print-tree.c | 17 ++++++++++++++---
>> 1 file changed, 14 insertions(+), 3 deletions(-)
>>
>> diff --git a/print-tree.c b/print-tree.c
>> index 3c585e31f1fc..687f871db302 100644
>> --- a/print-tree.c
>> +++ b/print-tree.c
>> @@ -803,14 +803,25 @@ 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 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];
>> +
>> + /* Reassemble the uuid from key.objecitd and key.offset */
>> + btrfs_item_key_to_cpu(l, &key, slot);
>> + put_unaligned_le64(key.objectid, uuid);
>> + put_unaligned_le64(key.offset, uuid + sizeof(u64));
>
> I don't think this will work on a BE system. Because
> btrfs_item_key_to_cpu take the LE representation on-disk and turns it
> into a cpu representation which might very well be BE. And then you
> essentially reverse it by using put_unaligned_le64 for x86 it works fine
> due to it being a LE system.
Ok, so looking at one of your other patches and some digging seems to
indicate that btrfs explicitly generates LE uuids so your code is
correct, however it's not obvoious from this patch itself. I suggest to
put either a comment above the put_unaligned or a statement in the
commit message that uuids are always generated in little-endian format
>
>
>> + 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 +1308,7 @@ 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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