Re: [PATCH RFC V3] new ioctl BTRFS_IOC_GET_CHUNK_INFO

[David Sterba <dsterba@suse.cz>]

On Thu, Mar 19, 2020 at 09:39:12PM +0100, Goffredo Baroncelli wrote:
> This patch creates a new ioctl BTRFS_IOC_GET_CHUNK_INFO.
> The aim is to replace the BTRFS_IOC_TREE_SEARCH ioctl
> used by "btrfs fi usage" to obtain information about the 
> chunks/block groups. 
> 
> The problems in using the BTRFS_IOC_TREE_SEARCH is that it access
> the very low data structure of BTRFS. This means: 
> 1) this would be complicated a possible change of the disk format
> 2) it requires the root privileges
> 
> The BTRFS_IOC_GET_CHUNK_INFO ioctl can be called even from a not root
> user: I think that the data exposed are not sensibile data.
> 
> These patches allow to use "btrfs fi usage" without root privileges.
> 
> before:
> -------------------------------------------
> 
> $ btrfs fi us /
> WARNING: cannot read detailed chunk info, per-device usage will not be shown, run as root
> Overall:
>     Device size:                 100.00GiB
>     Device allocated:             26.03GiB
>     Device unallocated:           73.97GiB
>     Device missing:                  0.00B
>     Used:                         17.12GiB
>     Free (estimated):             80.42GiB      (min: 80.42GiB)
>     Data ratio:                       1.00
>     Metadata ratio:                   1.00
>     Global reserve:               53.12MiB      (used: 0.00B)
> 
> Data,single: Size:23.00GiB, Used:16.54GiB (71.93%)
> 
> Metadata,single: Size:3.00GiB, Used:588.94MiB (19.17%)
> 
> System,single: Size:32.00MiB, Used:16.00KiB (0.05%)
> 
> after:
> -----------------------------------------------
> $ ./btrfs fi us /
> Overall:
>     Device size:                 100.00GiB
>     Device allocated:             26.03GiB
>     Device unallocated:           73.97GiB
>     Device missing:                  0.00B
>     Used:                         17.12GiB
>     Free (estimated):             80.42GiB      (min: 80.42GiB)
>     Data ratio:                       1.00
>     Metadata ratio:                   1.00
>     Global reserve:               53.12MiB      (used: 0.00B)
> 
> Data,single: Size:23.00GiB, Used:16.54GiB (71.93%)
>    /dev/sdd3      23.00GiB
> 
> Metadata,single: Size:3.00GiB, Used:588.94MiB (19.17%)
>    /dev/sdd3       3.00GiB
> 
> System,single: Size:32.00MiB, Used:16.00KiB (0.05%)
>    /dev/sdd3      32.00MiB
> 
> Unallocated:
>    /dev/sdd3      73.97GiB
> 
> Comments are welcome

I'm going to send more comments, the new ioctl is among features
considered for 5.9.