Re: [Xen-devel] [PATCH] libxlu: Handle += in config files

[Wei Liu <wl@xen.org>]

On Tue, Aug 13, 2019 at 05:42:15PM +0100, Anthony PERARD wrote:
> On Tue, Aug 13, 2019 at 04:47:23PM +0100, Andrew Cooper wrote:
> > Error between user and terminal. :)
> > 
> > I'd sync'd xl and libxl.so, but not libxlu.so
> 
> I actually made the same mistake first time I tried.
> 
> > Ok, so that is working now.  I think 'cmdline+=" dom0=pvh
> > dom0-iommu=none"' is slightly less tortured syntax, but I guess there is
> > no way that this isn't going to be horrible.
> > 
> > As for the general mechanism, how usable is += for anything other than
> > cmdline?  Most strings in config files can't usefully be extended in
> > this matter - if they need changing, they need changing wholesale.
> 
> That's true, but one could imaging some maybe bad example like adding a
> suffix to the name of the guest: "name+='-ovmf';".
> Going through `man xl.cfg', maybe a good example other than cmdline
> could be "cpus+=',^1'" but maybe a space is fine here, or one could use
> a list instead.
> Other potential uses could be for "PATH", but in this case it would be
> better reset the setting rather that attempting to add a suffix to an
> existing one.
> 
> I wonder if instead of doing += on all strings, we should instead have
> `xl' whitelist the few options where += would make sense. (and at that
> point, it would be easy to add a ' ' where is make sense, like
> "cmdline"s. But then, how to tell users that it can't do "name+='-new'"?
> because xlu would just print a warning, and xl would keep going with
> name="".  Try "xl create memory+=42" ;-).

Not sure I follow. Can you limit this in xl? Isn't += handled in libxlu
already?

Wei.

> 
> -- 
> Anthony PERARD

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