Re: [RFC] btrfs-progs: use the new ioctl BTRFS_IOC_GET_CHUNK_INFO

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Gentle ping.

BR
G.Baroncelli

On 3/15/20 4:24 PM, Goffredo Baroncelli wrote:> > Hi,>
this is a repost of an old patch (~2017). At the time it din't received
any feedback. I repost it hoping that it still be interested.

This patch set is the btrfs-prog related one; another one related to the
kernel is send separately.

This patch set createa 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
BR
G.Baroncelli




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