On 2017/10/30 17:32, Qu Wenruo wrote:
>
>
> On 2017年10月30日 16:14, Misono, Tomohiro wrote:
>> Currently, the top-level subvolume lacks the UUID. As a result, both
>> non-snapshot subvolume and snapshot of top-level subvolume do not have
>> Parent UUID and cannot be distinguisued. Therefore "fi show" of
>> top-level lists all the subvolumes which lacks the UUID in
>> "Snapshot(s)". Also, it lacks the otime information.
>
> What about creating a wiki page for ROOT_ITEM and detailed restriction
> for its members?
>
>>
>> Fix this by adding the UUID and otime at the mkfs time. As a
>> consequence, snapshots of top-level subvolume now have a Parent UUID and
>> UUID tree will create an entry for top-level subvolume at mount time.
>
> This patch also inspires me about the btrfs_create_tree() function I'm
> introducing should also populate its UUID and timespec.
>
>>
>> Signed-off-by: Tomohiro Misono <misono.tomohiro@xxxxxxxxxxxxxx>
>> ---
>> ctree.h | 5 +++++
>> mkfs/common.c | 14 ++++++++++++++
>> mkfs/main.c | 3 +++
>> 3 files changed, 22 insertions(+)
>>
>> diff --git a/ctree.h b/ctree.h
>> index 2280659..5737978 100644
>> --- a/ctree.h
>> +++ b/ctree.h
>> @@ -2071,6 +2071,11 @@ BTRFS_SETGET_STACK_FUNCS(root_stransid, struct btrfs_root_item,
>> stransid, 64);
>> BTRFS_SETGET_STACK_FUNCS(root_rtransid, struct btrfs_root_item,
>> rtransid, 64);
>> +static inline void btrfs_set_root_uuid(struct btrfs_root_item *root_item,
>> + u8 uuid[BTRFS_UUID_SIZE])
>> +{
>> + memcpy(root_item->uuid, uuid, BTRFS_UUID_SIZE);
>> +}
>
> This is the stack version.
>
> However there is no extent buffer version to set uuid as we just call
> write_extent_buffer(), so it seems unnecessary to me.
>
>>
>> /* struct btrfs_root_backup */
>> BTRFS_SETGET_STACK_FUNCS(backup_tree_root, struct btrfs_root_backup,
>> diff --git a/mkfs/common.c b/mkfs/common.c
>> index c9ce10d..808d343 100644
>> --- a/mkfs/common.c
>> +++ b/mkfs/common.c
>> @@ -44,6 +44,7 @@ static int btrfs_create_tree_root(int fd, struct btrfs_mkfs_config *cfg,
>> u32 itemoff;
>> int ret = 0;
>> int blk;
>> + u8 uuid[BTRFS_UUID_SIZE];
>>
>> memset(buf->data + sizeof(struct btrfs_header), 0,
>> cfg->nodesize - sizeof(struct btrfs_header));
>> @@ -77,6 +78,19 @@ static int btrfs_create_tree_root(int fd, struct btrfs_mkfs_config *cfg,
>> btrfs_set_item_offset(buf, btrfs_item_nr(nritems), itemoff);
>> btrfs_set_item_size(buf, btrfs_item_nr(nritems),
>> sizeof(root_item));
>> + if (blk == MKFS_FS_TREE) {
>> + time_t now = time(NULL);
>> +
>> + uuid_generate(uuid);
>> + btrfs_set_root_uuid(&root_item, uuid);
>> + btrfs_set_stack_timespec_sec(&root_item.otime, now);
>> + btrfs_set_stack_timespec_sec(&root_item.ctime, now);
>> + } else {
>> + memset(uuid, 0, BTRFS_UUID_SIZE);
>
> This leads to the question about the UUID meaning of different trees.
>
> AFAIK every tree created by kernel has its own UUID, no one uses all zero.
>
> In kernel btrfs_create_tree(), it always calls uuid_le_gen() to generate
> a new UUID.
> So I'm wonder if such branch is really needed.
> And maybe we fix all tree creation to generate UUID.
>
> Despite the question about the meaning of UUID for root_item, I think
> the patch really makes sense.
>
> Thanks,
> Qu
>
Hello,
Thanks for the whole comments.
I notice UUID (and otime/ctime) of ROOT_ITEM is not used nor updated currently
expect subvolumes. Therefore I think it is better to keep these fields to zero
to express non-used status. (So, it may be better that uuid/quota tree is not hold UUID.)
Regards,
Tomohiro
>> + btrfs_set_root_uuid(&root_item, uuid);
>> + btrfs_set_stack_timespec_sec(&root_item.otime, 0);
>> + btrfs_set_stack_timespec_sec(&root_item.ctime, 0);
>> + }
>> write_extent_buffer(buf, &root_item,
>> btrfs_item_ptr_offset(buf, nritems),
>> sizeof(root_item));
>> diff --git a/mkfs/main.c b/mkfs/main.c
>> index 1b4cabc..4184a2d 100644
>> --- a/mkfs/main.c
>> +++ b/mkfs/main.c
>> @@ -329,6 +329,7 @@ static int create_tree(struct btrfs_trans_handle *trans,
>> struct btrfs_key location;
>> struct btrfs_root_item root_item;
>> struct extent_buffer *tmp;
>> + u8 uuid[BTRFS_UUID_SIZE] = {0};
>> int ret;
>>
>> ret = btrfs_copy_root(trans, root, root->node, &tmp, objectid);
>> @@ -339,6 +340,8 @@ static int create_tree(struct btrfs_trans_handle *trans,
>> btrfs_set_root_bytenr(&root_item, tmp->start);
>> btrfs_set_root_level(&root_item, btrfs_header_level(tmp));
>> btrfs_set_root_generation(&root_item, trans->transid);
>> + /* clear uuid of source tree */
>> + btrfs_set_root_uuid(&root_item, uuid);
>> free_extent_buffer(tmp);
>>
>> location.objectid = objectid;
>>
>
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