This needs to be documented in RHEL 7 as well as RHEL 6

+++ This bug was initially created as a clone of Bug #1103923 +++

+++ This bug was initially created as a clone of Bug #867376 +++

I'm opening this to track and gather any ideas for this issue...

Sometimes we can see (in the scripts most notably) that the output needs to be laboriously parsed by external tools to filter out some of the output that is not actually needed or is even undesirable. Also, sometimes we need to run specific commands changing metadata or changing the activation status based on some other criteria than just PV/VG/LV name.

Examples of such criteria-based selection include reporting/displaying VGs that are clustered or local, or any other type-based criteria like mirror volumes, snapshot volumes, thin volumes, RAID volumes etc. Other criteria might be the size of the volume or whatever we report today in LVM display commands in general...

I think this would improve the way the scripts work with LVM commands. Also, the same filtering logic should probably be available via liblvm interface.

This is definitely not a high priority feature request, but just something that would be nice to have.

--- Additional comment from Fedora End Of Life on 2013-04-03 14:56:31 EDT ---

This bug appears to have been reported against 'rawhide' during the Fedora 19 development cycle.
Changing version to '19'.

(As we did not run this process for some time, it could affect also pre-Fedora 19 development
cycle bugs. We are very sorry. It will help us with cleanup during Fedora 19 End Of Life. Thank you.)

More information and reason for this action is here:
https://fedoraproject.org/wiki/BugZappers/HouseKeeping/Fedora19

--- Additional comment from David Teigland on 2014-04-11 12:24:41 EDT ---

It may make sense to borrow the command line "selection" syntax for bug 1070381.

We want to be able to select vgs from the command line by: name, uuid, tags.
If a uuid or tag is used, it requires reading all vg's to match against the
uuid/tag args.  If a name is used, only the vg's with the given names are
read.  So a command with a uuid/tag arg can be much more expensive.  People
can intentionally select vgs only by name to avoid this expense.

The problem is that people use uuids as names, and they are indistinct as
command line args: we do not know if the arg is meant as one or the other.
When a uuid arg is seen, the process_each_vg code has to read all vgs in
case the uuid arg will match a vg's uuid, not a name.

This means a person with uuids as names, who is selecting the vgs by name on
the command line would unavoidably pay the expense of reading all vgs.

A solution would be to know from the command line syntax if the arg is meant to
match a vg's name or uuid.  If we knew this up front, we could avoid
unnecessarily reading all vgs.

If the selection syntax were something like -o field=value, then:

1. vgs -o uuid=12-34-56-78
2. vgs -o name=12-34-56-78

The first command would read all vg's and attempt to match the uuid arg with
a vg's uuid.  The second command would only read the named vg.  Importantly,
this is not only an output filter, but selects the objects to be processed.

--- Additional comment from Peter Rajnoha on 2014-04-25 06:12:37 EDT ---

I've pushed a development branch 'dev-prajnoha-condout' with the code to support filtering report output (vgs, lvs, pvs, dmsetup as of now) based on conditions supplied: https://git.fedorahosted.org/cgit/lvm2.git/log/?h=dev-prajnoha-condout. This is actually rebased original version of the patchset.
The original code is dated back in 2007 and was written by Jun'ichi Nomura: http://www.redhat.com/archives/dm-devel/2007-April/msg00025.html.

I've added some improvements like support for comparing sizes with units...

I'd still like to explore a possibility to reuse part of this logic for conditional execution as well (e.g. change all LVs that comply with the condition supplied).

Still needs more testing, but the reporting part seems to work basically. 

Example:

[1] raw/~ # pvs
  PV         VG         Fmt  Attr PSize   PFree  
  /dev/sda   vg1        lvm2 a--  480.00m 440.00m
  /dev/sdb   vg1        lvm2 a--   96.00m  96.00m
  /dev/sdc   vg1        lvm2 a--  124.00m 124.00m
  /dev/sde   vg2        lvm2 a--  124.00m  72.00m
  /dev/sdf   vg2        lvm2 a--  124.00m 124.00m
  /dev/sdg   vg2        lvm2 a--  124.00m 124.00m
  /dev/sdh   other      lvm2 a--  124.00m  28.00m
  /dev/sdi   other      lvm2 a--  124.00m 124.00m
  /dev/vda2  fedora_raw lvm2 a--    9.50g      0 
[1] raw/~ # vgs
  VG         #PV #LV #SN Attr   VSize   VFree  
  fedora_raw   1   2   0 wz--n-   9.50g      0 
  other        2   2   0 wz--n- 248.00m 152.00m
  vg1          3   4   0 wz--n- 700.00m 660.00m
  vg2          3   4   0 wz--n- 372.00m 320.00m
[1] raw/~ # lvs
  LV    VG         Attr       LSize  
  root  fedora_raw -wi-ao----   9.00g
  swap  fedora_raw -wi-ao---- 512.00m
  one   other      -wi-a-----  32.00m
  two   other      -wi-a-----  64.00m
  lvol0 vg1        -wi-a-----   4.00m
  lvol1 vg1        -wi-a-----   8.00m
  lvol2 vg1        -wi-a-----  12.00m
  lvol3 vg1        -wi-a-----  16.00m
  lvol0 vg2        -wi-a-----   4.00m
  lvol1 vg2        -wi-a-----  12.00m
  lvol2 vg2        -wi-a-----  16.00m
  lvol3 vg2        -wi-a-----  20.00m
[1] raw/~ # pvs --condition 'pv_size > 200m'
  PV         VG         Fmt  Attr PSize   PFree  
  /dev/sda   vg1        lvm2 a--  480.00m 440.00m
  /dev/vda2  fedora_raw lvm2 a--    9.50g      0 
[1] raw/~ # pvs --condition '(pv_size > 200m) && (pv_size < 9g)'
  PV         VG   Fmt  Attr PSize   PFree  
  /dev/sda   vg1  lvm2 a--  480.00m 440.00m
[1] raw/~ # lvs --condition 'lv_name=~"lvol[023]"'
  LV    VG   Attr       LSize 
  lvol0 vg1  -wi-a-----  4.00m
  lvol2 vg1  -wi-a----- 12.00m
  lvol3 vg1  -wi-a----- 16.00m
  lvol0 vg2  -wi-a-----  4.00m
  lvol2 vg2  -wi-a----- 16.00m
  lvol3 vg2  -wi-a----- 20.00m
[1] raw/~ # lvs --condition '(lv_name=~"lvol[023]") || (lv_size > 500m)'
  LV    VG         Attr       LSize  
  root  fedora_raw -wi-ao----   9.00g
  swap  fedora_raw -wi-ao---- 512.00m
  lvol0 vg1        -wi-a-----   4.00m
  lvol2 vg1        -wi-a-----  12.00m
  lvol3 vg1        -wi-a-----  16.00m
  lvol0 vg2        -wi-a-----   4.00m
  lvol2 vg2        -wi-a-----  16.00m
  lvol3 vg2        -wi-a-----  20.00m
[1] raw/~ # lvs --condition 'lv_attr=~"ao"'
  LV   VG         Attr       LSize  
  root fedora_raw -wi-ao----   9.00g
  swap fedora_raw -wi-ao---- 512.00m

--- Additional comment from Peter Rajnoha on 2014-04-30 05:21:58 EDT ---

Second iteration of the patchset:
https://git.fedorahosted.org/cgit/lvm2.git/log/?h=dev-prajnoha-selout

- renamed --condition to -S/--select
- added -S/--select to pv/vg/lvdisplay (with -C)
- AND is "+" and OR is "," now
- "==" is "=" now
- no need to use quotes, so this works now:
   lvs --select name=abc,vg_name=def
- added a check whether a field referenced in the selection is recognized (so "lvs --select unknown" produces:

[0] raw # lvs -S bla=abc 
  Unrecognized selection field: bla
  Selection syntax error at 'bla=abc'

...now I'll try to add the coverage for list matching (e.g. tag list). So that will be in next iteration I hope...

--- Additional comment from Peter Rajnoha on 2014-05-29 06:20:11 EDT ---

Hopefully final candidate:
https://git.fedorahosted.org/cgit/lvm2.git/log/?h=dev-prajnoha-report-select

--- Additional comment from Steven J. Levine on 2014-06-02 17:38:18 EDT ---

Should have noted above:  This feature needs to be documented.

Alasdair's summary of the feature:

also, make a note that 'dumpconfig' also needs documenting some time
<agk> Peter's added a lot of features to it recently.

<agk> it now lets you generate default config files, compare your settings against the default etc.

<agk> find out what release a setting was introduced
<agk> it's pretty much undocumented anywhere at the moment
<agk> - to work with prajnoha to write a decent document about it
<agk> and one more new feature that will need a lot of documentation (6.6/7.1)
<agk> is --select
<agk> it's about to be committed upstream, but it'll be very useful for people
<agk> roughly it lets you say things like 'lvs --select size>10M'
<agk> to see only LVs bigger than 10Mb
<agk> (by a lot of documentation, I really mean "we want everyone to know about this and use it" rather than it taking a lot of time to document)