Re: adding "{mds,mon} metadata" asok command

[John Spray <john.spray@redhat.com>]

On 20/03/2015 05:39, kefu chai wrote:
> to pave the road to http://tracker.ceph.com/issues/10904, where we
> need to add a command to list the hostname of nodes in a ceph cluster,
> i would like to add the "{mds,mon} metadata" commands to print the
> system information including, but not limited to hostname,
> mem_{total,swap}_kb, and distro info, of specified mds and mon.
>
> the implementation follow the mechanism of "osd metadata":
>
> on the mds side i would like to reuse the MDSMonitor service:
> 1. piggy back a map for the metadata in MMDSBeacon message,
> 2. put the metadata into the same DBStore transaction but with another
> prefix when storing the pending inc into local storage.
> 3. and expose it using the "mds metadata" and later on the "service
> ls" (not sure about the name ...)
>
> @greg and @zyan, are you good with this? not sure this will overburden
> the mds or not. i will use uname(2) and grep /proc/meminfo to get the
> metadata in the same way of OSD.
It should be straightforward to include the metadata in MMDSBeacon only 
once per daemon lifetime, by checking if state is CEPH_MDS_STATE_BOOT -- 
that way we don't have to worry about any ongoing costs.  I expect that 
change can live entirely in Beacon.cc without touching any other MDS code.

As for the means of getting the information, I expect the generic 
kernel/mem/cpu/distro stuff from OSD::_collect_metadata can be moved up 
into common/ somewhere and reused as-is from mon+mds.

John