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.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 > 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; >> > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html