On 2/10/21 11:09 PM, Jens Axboe wrote:
> On 2/9/21 10:07 PM, Coly Li wrote:
>> +struct bch_nvm_pgalloc_recs {
>> +union {
>> + struct {
>> + struct bch_nvm_pages_owner_head *owner;
>> + struct bch_nvm_pgalloc_recs *next;
>> + __u8 magic[16];
>> + __u8 owner_uuid[16];
>> + __u32 size;
>> + __u32 used;
>> + __u64 _pad[4];
>> + struct bch_pgalloc_rec recs[];
>> + };
>> + __u8 pad[8192];
>> +};
>> +};
>
Hi Jens,
> This doesn't look right in a user header, any user API should be 32-bit
> and 64-bit agnostic.
The above data structure is stored in NVDIMM as allocator's meta data.
It is designed to be directly accessed (in future update) as in-memory
object, but stored on non-volatiled memory like on-disk data structure.
To me, it is fine to use unsigned int/long/long long to define the
members, because nvdimm driver only works on 64bit platform. It is just
unclear to me which form/style I should use to define such data
structure. On one side they are stores as non-volatiled media, on other
side they are accessed directly as in-memory object...
>
>> +struct bch_nvm_pages_owner_head {
>> + __u8 uuid[16];
>> + char label[BCH_NVM_PAGES_LABEL_SIZE];
>> + /* Per-namespace own lists */
>> + struct bch_nvm_pgalloc_recs *recs[BCH_NVM_PAGES_NAMESPACES_MAX];
>> +};
>
> Same here.
For the above pointer, it is the same reason. In later version, such
object on NVDIMM will be referenced directly by an in-memory pointer
like we normally do for an in-memory object.
Therefore I do treat the data structure as in-memory object after the
DAX mapping accomplished. If not define it as an in-memory pointer, I
have to cast it into (void *) every time when I use it.
>
>> +/* heads[0] is always for nvm_pages internal usage */
>> +struct bch_owner_list_head {
>> +union {
>> + struct {
>> + __u32 size;
>> + __u32 used;
>> + __u64 _pad[4];
>> + struct bch_nvm_pages_owner_head heads[];
>> + };
>> + __u8 pad[8192];
>> +};
>> +};
>
> And here.
>
>> +#define BCH_MAX_OWNER_LIST \
>> + ((sizeof(struct bch_owner_list_head) - \
>> + offsetof(struct bch_owner_list_head, heads)) / \
>> + sizeof(struct bch_nvm_pages_owner_head))
>> +
>> +/* The on-media bit order is local CPU order */
>> +struct bch_nvm_pages_sb {
>> + __u64 csum;
>> + __u64 ns_start;
>> + __u64 sb_offset;
>> + __u64 version;
>> + __u8 magic[16];
>> + __u8 uuid[16];
>> + __u32 page_size;
>> + __u32 total_namespaces_nr;
>> + __u32 this_namespace_nr;
>> + union {
>> + __u8 set_uuid[16];
>> + __u64 set_magic;
>> + };
>
> This doesn't look like it packs right either.
This is my mimicry from bcache code, which uses the least significant 8
bytes from the randomly generated UUID as a magic number. It is solid
and not changed during the whole life cycle for the nvm pages set.
>
>> +
>> + __u64 flags;
>> + __u64 seq;
>> +
>> + __u64 feature_compat;
>> + __u64 feature_incompat;
>> + __u64 feature_ro_compat;
>> +
>> + /* For allocable nvm pages from buddy systems */
>> + __u64 pages_offset;
>> + __u64 pages_total;
>> +
>> + __u64 pad[8];
>> +
>> + /* Only on the first name space */
>> + struct bch_owner_list_head *owner_list_head;
>
> And here's another pointer...
>
Same reason for I use it as an in-memory pointer.
The above definition is just using all the structures as in-memory
object, the difference is just they are non-volatiled after reboot.
Thanks.
Coly Li
