Re: [Xen-devel] [PATCH v1 01/10] libxl: libxl-json format and internal functions to get / set it

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Wei Liu writes ("[PATCH v1 01/10] libxl: libxl-json format and internal 
functions to get / set it"):
> Introduce a new format in libxl userdata store called "libxl-json". This
> file format contains JSON version of libxl_domain_config, generated by
> libxl.
...
> +int libxl__get_domain_configuration(libxl__gc *gc, uint32_t domid,
> +                                    libxl_domain_config *d_config)
> +{
> +    uint8_t *data = NULL;
> +    int rc, len;
> +
> +    rc = libxl_userdata_retrieve(CTX, domid, "libxl-json", &data, &len);
...
> +    if (len == 0) {
> +        LOGE(ERROR, "configuration data stream empty for domain %d", domid);
> +        rc = ERROR_FAIL;

Reading 03/10 I notice the following issue with this:

During domain setup there is a moment where the domid exists, but the
configuration data doesn't.  Therefore this is a possible situation,
and does not reflect an internal error.

So, you need to treat this case differently.  It shouldn't log an
error and it should probably return a custom error code, which all
callers would have to handle specially.

Ultimately if an application asks for the configuration of a domain in
this state, it is not possible to tell whether it is in the process
being created, or is left in an anomalous (crashed) state.  So I think
this possible but anomalous state needs to be exposed all the way up
the stack.

Ian.

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