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.tomoh...@jp.fujitsu.com>
> ---
> 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
> + 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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