[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3 5/5] tools: add example application to initialize dom0less PV drivers
Hi Stefano, On 23/03/2022 02:50, Stefano Stabellini wrote: On Sat, 29 Jan 2022, Julien Grall wrote:We are only using the struct xc_dom_image parameter forOn 28/01/2022 21:33, Stefano Stabellini wrote:+ libxl_uuid uuid; + uint64_t v; + int rc; + + printf("Init dom0less domain: %d\n", info->domid); + dom.guest_domid = info->domid; + dom.xenstore_domid = 0; + dom.xch = xc_interface_open(0, 0, 0); + + rc = xc_hvm_param_get(dom.xch, info->domid, HVM_PARAM_STORE_EVTCHN, &v); + if (rc != 0) { + printf("Failed to get HVM_PARAM_STORE_EVTCHN\n"); + return 1; + } + dom.xenstore_evtchn = v; + + /* Console won't be initialized but set its data for completeness */ + dom.console_domid = 0;I find a bit odd you set the domid but not the event channel, page. Can you explain? Actually, can you explain why only half of the structure is initialized?xc_dom_gnttab_init, and nothing else. We only need very few fields in it. Basically we could call xc_dom_gnttab_seed directly and then we wouldn't need struct xc_dom_image at all. Only the needed fields are currently populated. I would prefer if we don't use xc_dom_image and call xc_dom_gnttab_seed(). This would: 1) reduce the risk that one of the unitialized field is will be mistakenly use 2) extra documentation (currently missing) to explain which fields is used. Does this mean the caller will have to reboot the system if there is an error? IOW, we don't expect them to call ./init-dom0less twice.+ + /* Alloc magic pages */ + if (alloc_magic_pages(info, &dom) != 0) { + printf("Error on alloc magic pages\n"); + return 1; + } + + xc_dom_gnttab_init(&dom);This call as the risk to break the guest if the dom0 Linux doesn't support the acquire interface. This is because it will punch a hole in the domain memory where the grant-table may have already been mapped. Also, this function could fails.I'll check for return errors. Dom0less is for fully static configurations so I think it is OK to return error and abort if something unexpected happens: dom0less' main reason for being is that there is nothing unexpected :-) + + libxl_uuid_generate(&uuid); + xc_domain_sethandle(dom.xch, info->domid, libxl_uuid_bytearray(&uuid)); + + rc = gen_stub_json_config(info->domid, &uuid); + if (rc) + err(1, "gen_stub_json_config"); + + rc = restore_xenstore(xsh, info, uuid, dom.xenstore_evtchn); + if (rc) + err(1, "writing to xenstore"); + + xs_introduce_domain(xsh, info->domid, + (GUEST_MAGIC_BASE >> XC_PAGE_SHIFT) + XENSTORE_PFN_OFFSET, + dom.xenstore_evtchn);xs_introduce_domain() can technically fails.OK+ return 0; +} + +/* Check if domain has been configured in XS */ +static bool domain_exists(struct xs_handle *xsh, int domid) +{ + return xs_is_domain_introduced(xsh, domid); +}Would not this lead to initialize a domain with PV driver disabled?I am not sure I understood your question, but I'll try to answer anyway. This check is purely to distinguish dom0less guests, which needs further initializations, from regular guests (e.g. xl guests) that don't need any actions taken here. Dom0less domUs can be divided in two categories based on whether they are xen aware (e.g. xen,enhanced is set). Looking at this script, it seems to assume that all dom0less domUs are Xen aware. So it will end up to allocate Xenstore ring and call xs_introduce_domain(). I suspect the call will end up to fail because the event channel would be 0. So did you try to use this script on a platform where there only xen aware domU and/or a mix? Cheers, -- Julien Grall
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