Resend: API for retrieving linux lvm information

Hi:

I have ask about this before, however, i didn't any response.

I would appreciate very much if anyone can answer my question.

1) Is there any api library for retrieve linux lvm configuration? I.e. querying for all the vg(s), pv(s), lv(s) on the system?

2) If yes, what license is the library release under?

Thanks,

Stanley

These answers are for LVM2.

The commands: lvs, pvs, vgs with numerous cmdline flags. See lib/report/columns.h for field names

Access to cmds via library interface: configure --enable-cmdlib

include lvm2cmd.h

Example usage: doc/example_cmdlib.c

Recommend only manipulating one thing at once, so if it returns an error you don't have to work out which thing went wrong.

[May yet add an optional argc/argv-style entry point.]

The library API is intended to be LGPL.
It's effectively a wrapper around the command-line interface, but more efficient because it's able to cache some internal state between commands.
[I shall correct the copyright notices: the library entry-point got moved which messed up the original GPL/LGPL code split.]

liblvm.a does *not* provide a supported API and will sometimes change in subtle or incompatible ways without warning. Don't be tempted to link against it. The only interface supported is the one based on the command-line.

Alasdair

[email protected]

Alasdair:

Thanks for your response.

Given your last comment, I think i'm going to just perform the parsing from cmd-line or through /proc/lvm instead if using the apis.

As far as the parsing goes, is it better (in terms of compatibility, output stability) to parse against the command line output (i.e. lvdisplay) or against the /proc/filesystems (i.e. /proc/lvm/VGs/vg00/LVs)?

Also, it is unclear to me what is the meaning of each fields/values by looking at the information stored in the /proc/* by itself.

[root@DAP-RHLNX1 LVs]# cat /proc/lvm/VGs/vg00/LVs/vol1

name:         /dev/vg00/vol1
size:         409600
access:       3
status:       1
number:       0
open:         0
allocation:   0
device:       58:00

For example, what does it mean by "access: 3"?

Is all the information available from query apis (i.e. pvdisplay, lvdisplay) also available from the /proc/lvm subdirectories? How can we find out the meaning of each fields/value from the /proc/lvm information?

Thanks,

Stanley

My answer was for LVM2.
Looks like you're using LVM1.
To simplify your future upgrade you should consider using LVM2 tools lvs/pvs/vgs read-only even on an LVM1 installation as their output is designed to be easy to parse.

Alasdair

[email protected]

Thanks, Alasdair.

I'll indeed look into using LVM2.

I'm using Redhat AS 3.0.

Will the lvm2 rpm from Fedora Core work?
When will lvm2 be officially part of Redhat Enterprise Linux? How can i upgrade from an LVM1 system to LVM2? Is it just a matter of upgrading the rpm?

Thanks,

Stanley

liblvm.a seems handy, to generate lvm command line tools, but I'm missing a clear differentiation between modifying and non modifying usage.

I'm asking, as I want to develop some lvm information system running as a web service to provide a quick overview about my lvm configuration and status. Thus I definitely want to run it as non root. I might use those nice lvs,pvs,vgs commands, but I don't want to provide them with a suid-bit, as they are potentially able to modify my lvm. The former /proc interface was ideal for this purpose, but it seems to be missing for LVM2. Are there any plans, to provide lvm informations via /proc or /sys again, or would it be possible to write somehow "restricted" lvm-tools using liblvm?

Dieter.

Dieter St�ken, con terra GmbH, M�nster
    [email protected]
    http://www.conterra.de/
    (0)251-7474-501