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

[Bob Montgomery]

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