[PATCH][BTRFS-PROGS][V4] btrfs filesystem df

[Goffredo Baroncelli <kreijack@gmail.com>]

Hi Chris,

this serie of patches updated the command "btrfs filesystem
df". I update this command because it is not so easy to get
the information about the disk usage from the command "fi df" and "fi show".
This patch was the result of some discussions on the btrfs 
mailing list. Many thanks to all the contributors.

from the man page (see 2nd patch):

[...]
The  command  btrfs  filesystem  df is used to query the
status of the chunks, how many space on the disk(s) are used  by
the  chunks,  how many space are available in the chunks, and an
estimation of the free space of the filesystem.
[...]

$ ./btrfs filesystem df --help
usage: btrfs filesystem disk-usage [-k] <path> [<path>..]

    Show space usage information for a mount point(s).

    -k  Set KB (1024 bytes) as unit

$ ./btrfs filesystem df /
Path: /
Summary:
  Disk_size:                 72.57GB
  Disk_allocated:            25.10GB
  Disk_unallocated:          47.48GB
  Logical_size:              23.06GB
  Used:                      11.01GB
  Free_(Estimated):          55.66GB    (Max: 59.52GB, Min: 35.78GB)
  Data_to_disk_ratio:           92 %

Allocated_area:
  Type        Mode       Size_(disk)    Size_(logical)          Used
  Data        Single         21.01GB           21.01GB       12.77GB
  System      DUP            80.00MB           40.00MB        4.00KB
  System      Single          4.00MB            4.00MB          0.00
  Metadata    DUP             4.00GB            2.00GB      709.63MB
  Metadata    Single          8.00MB            8.00MB          0.00

Where:
        Disk_size                       -> sum of sizes of teh disks
        Disk_allocated                  -> sum of chunk sizes
        Disk_unallocated                -> Disk_size - Disk_allocated
        Logical_size                    -> sum of logical area sizes
        Used                            -> logical area used
        Free_(Estimated)                -> on the basis of allocated
                                           chunk, an estrapolation of
                                           the free space
        Data_to_disk_ratio              -> ration between the space occuped
                                           by a chunk and the real space
                                           available ( due to duplication
                                           and/or RAID level)
        Type				-> kind of chunk
        Mode                            -> allocation policy of a chunk
        Size_(disk)                     -> area of disk(s) occuped by the
                                           chunk (see it as raw space used)
        Size_(logical)                  -> logical area size of the chunk
        Used                            -> portion of the logical area
                                           used by the filesystem



You can pull this change from
   http://cassiopea.homelinux.net/git/btrfs-progs-unstable.git
branch
   disk_free

Please pull.

BR
Goffredo Baroncelli

Changelog:
V3->V4		Removed the switch -d -s from getopt(), aligned the
		column Size_(logical), renamed the fields:
		- Details -> Allocated_area
		- Chunk_type -> Type
V2->V3          Removed the options '-s' and '-d'; replaced Chunk-size 
                and Logical-size with Size_(disk) and Size_(logical).
                Update the man page.
V1->V2          Uses getopt(); replace "-" with "_"; change the behaviour
                of the switches '-s' and '-d'.
V0->V1          Change the name of command from disk-usage to df