On 15/07/2020 11:03, Coly Li wrote:
> On 2020/7/15 14:02, Hannes Reinecke wrote:
>> On 7/15/20 7:45 AM, Coly Li wrote:
>>> This patch adds comments to mark each member of struct cache_sb_disk,
>>> it is helpful to understand the bcache superblock on-disk layout.
>>>
>>> Signed-off-by: Coly Li <colyli@xxxxxxx>
>>> ---
>>> include/uapi/linux/bcache.h | 39 +++++++++++++++++++------------------
>>> 1 file changed, 20 insertions(+), 19 deletions(-)
>>>
>>> diff --git a/include/uapi/linux/bcache.h b/include/uapi/linux/bcache.h
>>> index 9a1965c6c3d0..afbd1b56a661 100644
>>> --- a/include/uapi/linux/bcache.h
>>> +++ b/include/uapi/linux/bcache.h
>>> @@ -158,33 +158,33 @@ static inline struct bkey *bkey_idx(const struct
>>> bkey *k, unsigned int nr_keys)
>>> #define BDEV_DATA_START_DEFAULT 16 /* sectors */
>>> struct cache_sb_disk {
>>> - __le64 csum;
>>> - __le64 offset; /* sector where this sb was written */
>>> - __le64 version;
>>> +/*000*/ __le64 csum;
>>> +/*008*/ __le64 offset; /* sector where this sb was
>>> written */
>>> +/*010*/ __le64 version;
>>> - __u8 magic[16];
>>> +/*018*/ __u8 magic[16];
>>> - __u8 uuid[16];
>>> +/*028*/ __u8 uuid[16];
>>> union {
>>> - __u8 set_uuid[16];
>>> +/*038*/ __u8 set_uuid[16];
>>> __le64 set_magic;
>>> };
>>> - __u8 label[SB_LABEL_SIZE];
>>> +/*048*/ __u8 label[SB_LABEL_SIZE];
>>> - __le64 flags;
>>> - __le64 seq;
>>> - __le64 pad[8];
>>> +/*068*/ __le64 flags;
>>> +/*070*/ __le64 seq;
>>> +/*078*/ __le64 pad[8];
>>> union {
>>> struct {
>>> /* Cache devices */
>>> - __le64 nbuckets; /* device size */
>>> +/*0b8*/ __le64 nbuckets; /* device size */
>>> - __le16 block_size; /* sectors */
>>> - __le16 bucket_size; /* sectors */
>>> +/*0c0*/ __le16 block_size; /* sectors */
>>> +/*0c2*/ __le16 bucket_size; /* sectors */
>>> - __le16 nr_in_set;
>>> - __le16 nr_this_dev;
>>> +/*0c4*/ __le16 nr_in_set;
>>> +/*0c6*/ __le16 nr_this_dev;
>>> };
>>> struct {
>>> /* Backing devices */
>>> @@ -198,14 +198,15 @@ struct cache_sb_disk {
>>> };
>>> };
>>> - __le32 last_mount; /* time overflow in y2106 */
>>> +/*0c8*/ __le32 last_mount; /* time overflow in y2106 */
>>> - __le16 first_bucket;
>>> +/*0cc*/ __le16 first_bucket;
>>> union {
>>> - __le16 njournal_buckets;
>>> +/*0ce*/ __le16 njournal_buckets;
>>> __le16 keys;
>>> };
>>> - __le64 d[SB_JOURNAL_BUCKETS]; /* journal buckets */
>>> +/*0d0*/ __le64 d[SB_JOURNAL_BUCKETS]; /* journal
>>> buckets */
>>> +/*8d0*/
>>> };
>>> struct cache_sb {
>>>
>> Common practice is to place comments at the end; please don't use the
>> start of the line here.
>
> Hi Hannes,
>
> When I try to move the offset comment to the line end, I find it
> conflicts with normal code comment, e.g.
> __le64 d[SB_JOURNAL_BUCKETS]; /* journal buckets */
>
> I have to add the offset comment to the line start. I guess this is why
> ocfs2 code adds the offset comment at the line start.
>
> So finally I have to keep the offset comment on line start still...
Why at them at all? pahole -C or crash/gdb will show them for you if you're
interested and if you need it in the code you can use offsetof().
I don't really see a good reason to add these comments.
