Re: [Crash-utility] xendump image with full-vitualized domain

Kazuo Moriwaka wrote: Yes, I agree -- there will have to be a design change to the xendump-creation code. Upon revisiting the current xendump-creation code, it see now that it would be impossible to write a post-dump tool to create a usable dumpfile, because that tool would need the pfn-to-mfn mapping information that would only be available when the guest kernel was active. It's unfortunate that the current xendump format doesn't maintain a true pfn-to-mfn mapping. When I first starting working with xendumps, I thought that was true, only to find out that it is not. The xendump header looks like this: typedef struct xc_core_header { unsigned int xch_magic; unsigned int xch_nr_vcpus; unsigned int xch_nr_pages; unsigned int xch_ctxt_offset; unsigned int xch_index_offset; unsigned int xch_pages_offset; } xc_core_header_t; The number of pages in the xendump is "xch_nr_pages", which I believe is all of the guest domain pfn's that happened to be instantiated with a xen mfn at the time of the dump. Therefore, in all xendumps that I've seen, "xch_nr_pages" is always less than the number of pages that the guest "thinks" that it has. So anyway, starting at "xch_index_offset", there is an array of "xch_nr_pages" xen_pfn_t values, which are actually mfn values. And starting at "xch_pages_offset", there is an array of "xch_nr_pages" page data contents. Essentially there is this: xen_pfn_t xch_index_offset[xch_nr_pages]; char xch_pages_offset[xch_nr_pages][PAGE_SIZE]; So for any mfn found at a given index into the array at xch_index_offset, the page data for that mfn is found at the same index into the page data array at xch_pages_offset. When I first starting working with this, I presumed that the index into both arrays was based upon the pfn of the guest kernel, and therefore that it would be a really simple to translate pfn values from the vmlinux file into mfn values -- and therefore to get its data. And that is true at the beginning of the 2 xendump arrays -- but only so far into the arrays -- because eventually when a guest pfn is not instantiated with an mfn, it gets "skipped" in both arrays. Therefore, with each skipped pfn, the pfn-to-mfn relationship gets farther and farther out of sync. Unfortunately there is no way of telling when the first pfn gets skipped. It would have been ideal if they put in "non-existent" mfn markers in the first array and sparse file space in the second array if the pfn was not instantiated with an mfn... Anyway, that being the case, I needed to use the pfn-to-mfn translation mechanism used by the para-virtualized vmlinux kernel itself, that being the phys_to_machine_mapping[] array built into the guest kernel. That array is a one-to-one mapping of pfns to mfns, where non-existent mfns are actually marked as such. And once I get an mfn from the table in the guest kernel, the xendump can be searched for that mfn and then its page data. So, you are correct, I see no other choice except to have a new xendump format that also contains the pfn-to-mfn mapping information. Dave