Re: [RFC] Plumbing-only support for storing object metadata

From: Scott Chacon <schacon@gmail.com>
Date: Aug 9, 2008, 21:49 UTC
Message-ID: <d411cc4a0808091449n7e0c9b7et7980cf668106aead@mail.gmail.com>
In-Reply-To: <20080809210733.GA6637@oh.minilop.net>

Show 22 quoted lines

> We began trying to implement this proposal, but we found this enum
> definition in cache.h, which made us think there's only room for one
> more kind of object:
>
>        enum object_type {
>                OBJ_BAD = -1,
>                OBJ_NONE = 0,
>                OBJ_COMMIT = 1,
>                OBJ_TREE = 2,
>                OBJ_BLOB = 3,
>                OBJ_TAG = 4,
>                /* 5 for future expansion */
>                OBJ_OFS_DELTA = 6,
>                OBJ_REF_DELTA = 7,
>                OBJ_ANY,
>                OBJ_MAX,
>        };
>
> Do these object_type values appear in any on-disk structure, or does any
> other reason exist why this set of values cannot change? Can we add
> additional object types for inodes and props? If not, what would you
> recommend instead?

If I'm not mistaken, these are the values used to identify data in the header sections of packfile objects. The first four bits are used to identify the object type, where the first bit is static and the next three are the object type of the data following the header. Since the type is encoded using those three bits, 0-7 is the valid range. I would assume that would be difficult to change, since all the packfiles depend on that range.

Scott