Re: [Crash-utility] handling missing kdump pages in diskdump format

The change in analysis behavior requires a change to crash. Basically, I'd like crash to say "I don't know what is at that address" when it doesn't have the page in the dump instead of "That address contains a zero and it might be because it really was a zero and it might be because I don't what was there". Attached is a patch for crash (3.19) that causes it to quit providing zero'd pages for pages omitted from a KDUMP-style diskdump dumpfile. Note that this patch preserves the old behavior for DISKDUMP dumpfiles. (copied here for quick reference) --- crash-4.0-3.19/diskdump.c 2007-02-07 11:49:15.000000000 -0700 +++ crash-4.0-3.19.bobm/diskdump.c 2007-03-01 11:06:54.000000000 -0700 @@ -452,6 +452,8 @@ read_diskdump(int fd, void *bufptr, int if ((pfn >= dd->header->max_mapnr) || !page_is_ram(pfn)) return SEEK_ERROR; if (!page_is_dumpable(pfn)) { + if (dd->flags & KDUMP_CMPRS_LOCAL) + return SEEK_ERROR; memset(bufptr, 0, cnt); return cnt; }

If a user has old KDUMP dumpfiles generated by a version of makedumpfile that omits zero pages and wants to continue to debug with them, one workaround is to "fix" those dumpfiles to work with this newer version of crash by changing the first 8 bytes of the dumpfile from: "KDUMP " to "DISKDUMP" Otherwise, crash would either need a command line option to allow it to function with old zero-excluded makedumpfile dumps, or we would need to distinguish the zero-fill rule in the dumpfile header ("KDUMP " -> "KDUMP-NZ ") perhaps?

I will take a look at the behavior of crash on ELF format dumpfiles next week.