kdump: add is_vmcore_usable() and vmcore_unusable()

The usage of elfcorehdr_addr has changed recently such that being set to
ELFCORE_ADDR_MAX is used by is_kdump_kernel() to indicate if the code is
executing in a kernel executed as a crash kernel.

However, arch/ia64/kernel/setup.c:reserve_elfcorehdr will rest
elfcorehdr_addr to ELFCORE_ADDR_MAX on error, which means any subsequent
calls to is_kdump_kernel() will return 0, even though they should return
1.

Ok, at this point in time there are no subsequent calls, but I think its
fair to say that there is ample scope for error or at the very least
confusion.

This patch add an extra state, ELFCORE_ADDR_ERR, which indicates that
elfcorehdr_addr was passed on the command line, and thus execution is
taking place in a crashdump kernel, but vmcore can't be used for some
reason.  This is tested for using is_vmcore_usable() and set using
vmcore_unusable().  A subsequent patch makes use of this new code.

To summarise, the states that elfcorehdr_addr can now be in are as follows:

ELFCORE_ADDR_MAX: not a crashdump kernel
ELFCORE_ADDR_ERR: crashdump kernel but vmcore is unusable
any other value:  crash dump kernel and vmcore is usable

Signed-off-by: Simon Horman <horms@verge.net.au>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
index 4c65ca4..cd9ca67 100644
--- a/fs/proc/vmcore.c
+++ b/fs/proc/vmcore.c
@@ -644,7 +644,7 @@ static int __init vmcore_init(void)
 	int rc = 0;
 
 	/* If elfcorehdr= has been passed in cmdline, then capture the dump.*/
-	if (!(elfcorehdr_addr < ELFCORE_ADDR_MAX))
+	if (!(is_vmcore_usable()))
 		return rc;
 	rc = parse_crash_elf_headers();
 	if (rc) {