Re: [RFC] BTRFS_DEV_REPLACE_ITEM_STATE_* doesn't match with on disk

[Nikolay Borisov <nborisov@suse.com>]

On 12.11.18 г. 6:58 ч., Anand Jain wrote:
> 
> The dev_replace_state defines are miss matched between the
> BTRFS_IOCTL_DEV_REPLACE_STATE_* and BTRFS_DEV_REPLACE_ITEM_STATE_* [1].
> 
> [1]
> -----------------------------
> btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_FINISHED        2
> btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_CANCELED        3
> btrfs.h:#define BTRFS_IOCTL_DEV_REPLACE_STATE_SUSPENDED        4
> 
> btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_SUSPENDED    2
> btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_FINISHED    3
> btrfs_tree.h:#define BTRFS_DEV_REPLACE_ITEM_STATE_CANCELED    4
> -----------------------------
> 
> The BTRFS_DEV_REPLACE_ITEM_STATE_* series is unused in both btrfs.ko and
> btrfs-progs, the on-disk also follows BTRFS_IOCTL_DEV_REPLACE_STATE_*
> (we set dev_replace->replace_state using the
> BTRFS_IOCTL_DEV_REPLACE_STATE_* defines and write to the on-disk).
> 
>  359         btrfs_set_dev_replace_replace_state(eb, ptr,
>  360                 dev_replace->replace_state);
> 
> IMO it should be ok to delete the BTRFS_DEV_REPLACE_ITEM_STATE_*
> altogether? But how about the userland progs other than btrfs-progs?
> If not at least fix the miss match as in [2], any comments?

Unfortunately you are right. This seems to stem from sloppy job back in
the days of initial dev-replace support. BTRFS_DEV_REPLACE_ITEM_STATE_*
were added in e922e087a35c ("Btrfs: enhance btrfs structures for device
replace support"), yet they were never used. And the
IOCTL_DEV_REPLACE_STATE* were added in e93c89c1aaaa ("Btrfs: add new
sources for device replace code").

It looks like the ITEM_STATE* definitions were stillborn so to speak and
personally I'm in favor of removing them. They shouldn't have been
merged in the first place and indeed the patch doesn't even have a
Reviewed-by tag. So it originated from the, I'd say, spartan days of
btrfs development...

David,  any code which is using BTRFS_DEV_REPLACE_ITEM_STATE_SUSPENDED
is inherently broken, so how about we remove those definitions, then
when it's compilation is broken in the future the author will actually
have a chance to fix it, though it's highly unlikely anyone is relying
on those definitions.


> 
> [2]
> --------------------------------------
> diff --git a/include/uapi/linux/btrfs_tree.h
> b/include/uapi/linux/btrfs_tree.h
> index aff1356c2bb8..9ffa7534cadf 100644
> --- a/include/uapi/linux/btrfs_tree.h
> +++ b/include/uapi/linux/btrfs_tree.h
> @@ -805,9 +805,9 @@ struct btrfs_dev_stats_item {
>  #define BTRFS_DEV_REPLACE_ITEM_CONT_READING_FROM_SRCDEV_MODE_AVOID     1
>  #define BTRFS_DEV_REPLACE_ITEM_STATE_NEVER_STARTED     0
>  #define BTRFS_DEV_REPLACE_ITEM_STATE_STARTED           1
> -#define BTRFS_DEV_REPLACE_ITEM_STATE_SUSPENDED         2
> -#define BTRFS_DEV_REPLACE_ITEM_STATE_FINISHED          3
> -#define BTRFS_DEV_REPLACE_ITEM_STATE_CANCELED          4
> +#define BTRFS_DEV_REPLACE_ITEM_STATE_FINISHED          2
> +#define BTRFS_DEV_REPLACE_ITEM_STATE_CANCELED          3
> +#define BTRFS_DEV_REPLACE_ITEM_STATE_SUSPENDED         4
> 
>  struct btrfs_dev_replace_item {
>         /*
> --------------------------------------
> 
> 
> Thanks, Anand
>