On Tuesday, 09 November, 2010, João Eduardo Luís wrote:
> > The old tree is discarded unless the user requested a snapshot of it.
> >
> > Every time btrfs updates the roots is a new generation. Some data
> > structures have "generation" fields, indicating the generation in which
> > they were most recently changed. This is mostly used to verify the
> > filesystem is correct, but it's also possible to scan the generation
> > fields and find out which files have changed.
>
> As Goffredo Baroncelli explained in a previous reply to my questions, the
"find-new" command will search through keys with type BTRFS_EXTENT_DATA_TYPE.
This command does print several changes to the same files throughout history
since a given generation. My new question to this is rather simple: does BTRFS
actually keep the data from this generations to which "find-new" has access,
or is it only able to access information that records this changes?
>
Btrfs stores the info in a btree. With the exception of the leaf, every block
of the tree contains a list of a pair of key, pointer defined by the struct
btrfs_key_ptr:
struct btrfs_disk_key {
__le64 objectid;
u8 type;
__le64 offset;
} __attribute__ ((__packed__));
struct btrfs_key_ptr {
struct btrfs_disk_key key;
__le64 blockptr;
__le64 generation;
} __attribute__ ((__packed__));
The generation field, contains the info in which you are interested.
So I think that the correct answer of your question is the second one.
Regards
G.Baroncelli
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