Re: [Xen-devel] [PATCH V5 31/32] libxl: update domain configuration when updating memory targets

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-05-20 at 17:03 +0100, Ian Jackson wrote:
> Ian Campbell writes ("Re: [PATCH V5 31/32] libxl: update domain configuration 
> when updating memory targets"):
> > On Tue, 2014-05-20 at 16:44 +0100, Ian Jackson wrote:
> > > Merging the lists from libxl_device_disk_list and the JSON
> > > configuration shouldn't be too hard and will eliminate a lot of worry
> > > about races.
> > 
> > I think the presence of defaults in the libxl API makes it hard.
> 
> What I'm suggesting for the implementation of "get list of disks for
> retreived configuration" is something like this:
> 
>   * Read JSON with list of stored disk configs
> 
>   * Iterate over actual devices a la libxl_device_disk_list
>     * For each device, look for corresponding configuration in
>       disk config.
>       * If no such configuration, print a warning and make one up
>         along the lines of libxl_device_disk_getinfo
>       * If there was such a configuration, update the dynamically
>         adjustable fields by copying them from xenstore:
>          * currently, I think this is only the backing device
>            info (which can be modified dynamically for cds at least)
>     * Add resulting disk config to new list of disk configs
> 
>   * Replace stored list of disk configs with new one
> 
> The effect is that the pre-defaulted configuration takes precedence
> but that it is safe to write a JSON configuration containing devices
> which are about to be added.

It sounds workable to me, but I'll leave it up to Wei to poke holes in
it since he has been closer to this stuff...

Ian.



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