On 05/16/2013 18:19, David Sterba wrote:
On Thu, May 16, 2013 at 04:45:55PM +0200, Stefan Behrens wrote:+struct btrfs_uuid_item { + __le16 type; /* refer to BTRFS_UUID_ITEM_TYPE* defines above */ + __le32 len; /* number of following 64bit values */ + __le64 data[0]; /* data aligned to 64bit */ +} __attribute__ ((__packed__));With __packed__ (which is preferrably written as __packed) the data is not aligned to u64 as the comment says. Aligning u64's is a good thing, so (for example) pad the space after type (I don't think we need more than u16 here).
The on-disk format is in general not aligned (it is "packed") and stored on any byte-aligned position on the disk.
In the source code, you can use it for sizeof(), otherwise you use the access functions from ctree.h and struct-funcs.c.
I know that you know this already :) Maybe I am not understanding your review comment?
The "data" part in the btrfs_uuid_item (which represents the "value" of the (type, length, value) tripple) is a multiple of 64 bits, that's what I mean with the "data aligned to 64bit" comment.
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