[libvirt] [PATCHv2 2/4] network: change location of network state xml files

[John Ferlan]

On 04/17/2014 07:43 AM, Laine Stump wrote:
> For some reason these have been stored in /var/lib, although other
> drivers (e.g. qemu and lxc) store their state files in /var/run.
> 
> It's much nicer to store state files in /var/run because it is
> automatically cleared out when the system reboots. We can then use
> existence of the state file as a convenient indicator of whether or
> not a particular network is active.
> 
> Since changing the location of the state files by itself will cause
> problems in the case of a *live* upgrade from an older libvirt that
> uses /var/lib (because current status of active networks will be
> lost), the network driver initialization has been modified to migrate
> any network state files from /var/lib to /var/run.
> 
> This will not help those trying to *downgrade*, but in practice this
> will only be problematic in two cases
> 
> 1) If there are networks with network-wide bandwidth limits configured
>    *and in use* by a guest during a downgrade to "old" libvirt. In this
>    case, the class ID's used for that network's tc rules, as well as
>    the currently in-use bandwidth "floor" will be forgotten.
> 
> 2) If someone does this: 1) upgrade libvirt, 2) downgrade libvirt, 3)
>    modify running state of network (e.g. add a static dhcp host, etc),
>    4) upgrade. In this case, the modifications to the running network
>    will be lost (but not any persistent changes to the network's
>    config).
> ---
> change from V1:
> 
> * merged previous 2/5 & 3/5 into a single patch that changes the
>   location and migrates old state files, to avoid potential problems
>   by people trying to use git bisect.
> 
> * move the files with a direct copy, rather than reading/parsing the
>   XML then formatting/writing it. Note (hopefully) correct use of
>   readdir!
> 
> * put the migration into a separate static function
> 
> * don't put oldStateDir in driverState, as we only use it once during
>   initialization.
> 
> * only attempt migration when running privileged, since the
>   unprivileged state location hasn't changed.
> 
>  src/network/bridge_driver.c | 97 ++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 91 insertions(+), 6 deletions(-)
> 

ACK; however... Your call if you want to wait for virDirRead() from:

http://www.redhat.com/archives/libvir-list/2014-April/msg00745.html

Then refactor your for (;;) loop to use it...

I'm "assuming" the files cannot be adjusted during the period when
libvirt is "migrating" by any other "legal" :-) means. Just typing "out
loud" since your v1 would lock the network object and save the status in
the new location.

John