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

Hi Bob, Dave, On Wed, 08 Nov 2006 16:08:08 -0500, Dave Anderson wrote: >Bob Montgomery wrote: > >> I've been experimenting with the makedumpfile utility for kdump on ia64. >> One of my experiments was to verify that a page that should have been >> missing indeed was missing. I used crash 4.0-3.8 to look for a user >> page that should have been omitted from the dump. >> >> crash> x/xg 0xe0000040fc00c000 >> 0xe0000040fc00c000: 0x0000000000000000 >> >> On a full dump from makedumpfile as well as on a straight copy of >> vmcore, crash reports this: >> >> crash> x/xg 0xe0000040fc00c000 >> 0xe0000040fc00c000: 0x00010102464c457f >> >> The dumpfiles created by makedumpfile appear to crash as diskdump files, >> and crash appears to excuse missing pages and report 0x0 contents here: >> >> diskdump.c:read_diskdump, line 454: >> >> if (!page_is_dumpable(pfn)) { >> memset(bufptr, 0, cnt); >> return cnt; >> >> Shouldn't there be some indication that a requested page is missing as >> opposed to being legitimately full of zeros? >> >> Bob Montgomery > >Hi Bob, > >That decision was made by the diskdump developers >when I accepted their diskdump-specific work into the >crash utility. > >As I recall, I kind of agreed with you at the time, but there >was some compelling reason that they had that argued for >passing a zero-filled page -- although I don't recall what it >was? > >I don't believe it had anything to do with user pages, >but in the case of some of the other kernel pages that can >be left out of the dump, passing back a zero-filled page >was a cleaner way to handle whatever the problem was. > >Anyway, I've long since forgotten why they wanted it >that way... > >Perhaps the diskdump guys on this list can refresh my >memory? My memory is also unclear... As far as my dim memory goes, I decided the following policy when I wrote this code. 1) If the page is not found because of invalid address(e.g. address points memory hole), read_diskdump should return error. 2) If the page is not found because of partial dump, read_diskdump should return zero-filled page. Perhaps I decided the 2nd policy because of simplicity of implementation. Bob points out that crash should do something instead of passing zero-filled page (e.g. showing message) in the 2nd case, right?