[zfs-code] New ZAP object based on Micro-ZAP

[Girish Shilamkar]

Hi,
        While using DMU for lustre we need to store some extra information in
directory entries which is required for lustre operations. The size of
typical entries to be stored in directory entries are 16 bytes, hence we
can't use micro zap. And we would like to avoid using fat zap as not
many entries will be stored.
        Hence we thought about implementing a new ZAP object, something based
on mzap where all fields except the value field are the same. The format
would be something like this :

                typedef struct new_mzap_ent_phys {
                        uint64_t new_mze_value[2];
                        uint32_t new_mze_cd;
                        uint16_t new_mze_pad;       /* in case we want to chain 
them
someday */
                        char new_mze_name[NEW_MZAP_NAME_LEN];
                } new_mzap_ent_phys_t;

#define NEW_MZAP_LEN    64
#define NEW_MZAP_NAME_LEN (NEW_MZAP_LEN - 16 - 4 - 2)

Comments/Suggestions about it are most welcome.

Thanks & Regards,
Girish