Re: [Xen-devel] [PATCH 5/6] libxl: allow creation of domains with specified or random domid

[Ian Jackson <ian.jackson@xxxxxxxxxx>]

Paul Durrant writes ("[PATCH 5/6] libxl: allow creation of domains with 
specified or random domid"):
> This patch modifies do_domain_create() to use the value of domid that is
> passed in. A new 'special value' - RANDOM_DOMID - is added into the API
> and this, INVALID_DOMID or any valid domid is passed unmodified to
> libxl__domain_make(). Any other invalid domid value will cause an error.
> 
> If RANDOM_DOMID is passed in then libxl__domain_make() will use
> libxl__random_bytes() to choose a domid. If the chosen value is not a
> valid domid then this step will be repeated. Once a valid value is chosen
> it will be passed to xc_domain_create() but if this fails with an errno
> value of EEXIST, a new random value will be chosen and the operation will
> be retried.

What is the use case for this ?

I think using this is hazardous if you ever destroy domains, because
it will lead to reuse of domids in circumstances[1] where right now
that can't happen.

[1] Fewer than ~2^16 creations per Xen boot.

Ian.

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