Re: [Crash-utility] add support for incomplete elf dump file

With the patch I that proposed, you can simplify this part of your patch: + unsigned int e_flag = (NULL == nd->elf64) ? + (nd->elf32)->e_flags : (nd->elf64)->e_flags; + int status = e_flag& DUMP_ELF_INCOMPLETE; + if (status&& read_ret>= 0) { to just this: if (is_incomplete_dump()&& (read_ret>= 0)) { But what about compressed kdumps? In the case of DUMP_DH_COMPRESSED_INCOMPLETE dumpfiles, will makedumpfile manipulate the bitmaps and the page_desc.offset values of all "missing" pages to point to the special "pd_zero" page? Will it be impossible to distinguish between legitimate zero-filled pages and "missing" pages? I suppose that if that is true, then the behavior should be the same for both ELF and compressed kdumps, which would be to return zero-filled data. On the other hand... What's bothersome about automatically returning zero-filled data is that, currently, if an ELF vmcore was originally created correctly, but gets truncated *after* the fact, for example, when downloading it from a customer site, check_dumpfile_size() will report the error. But when data from the truncated region gets read, a read error is returned. If zero-filled data is silently returned, I can imagine that there will be all kinds of errors that will occur -- both display/content errors, but it could easily cause SIGSEGV's in the crash utility when it tries to use zero-filled data thinking that it's legitimate. How would the user even know whether it's because the page was truncated or not?

The crash utility already has a --zero_excluded flag for returning zero-filled memory if by chance a*legitimately* excluded/filtered page is read. It's hardly ever used, because those pages should never be required. But I wonder whether it could be re-purposed in this case, where by default an error would be returned when reading missing pages, and zero-filled only if it is explicitly requested with the --zero_excluded command line option? Or would that be impossible with DUMP_DH_COMPRESSED_INCOMPLETE compressed kdumps?