[Crash-utility] [PATCH 1/1 V4] crash: initial note of excluded page structures

[cpw]

Version 4 
- Makes the warning:

WARNING: The vmemmap page structures that are associated with the      
         memory pages excluded by the "makedumpfile -d <level>"
         option have been excluded from this dump.
         The administrator has used "makedumpfile -e".
         This will cause failures in any command that accesses a page
         structure of a page that is not included in the dump.  This
         is particularly likely when using several options of the
         kmem command.

Version 3 
- Changes the warning to be more complete:

WARNING: All unused vmemmap page structures are excluded from this dump.
         This will cause failures of the kmem command if it attempts to
         walk any list of free pages (with options such as -f -F -i -s
         and -S) or interpret an address with kmem <address>, and
         incorrect output from kmem -p.

Version 2 
- Moves the warning to this point:
      ...
      This GDB was configured as "x86_64-unknown-linux-gnu"...

      WARNING: All unused vmemmap page structures are excluded from this dump.
               This will cause failures of the kmem command if it attempts to
               walk any list of free pages (with options -f -F -i -s and -S).

        SYSTEM MAP: /boot/System.map-2.6.32-cpw
      ...

- Drop patch 2, which added warnings to individual kmem options.

- Feel free to change the wording of the warning.

And this patch is contingent upon the acceptance of a change to the
makedumpfile command.   
   http://marc.info/?l=kexec&m=138853299130125&w=2
  

If makedumpfile excludes unused page structures it will flag that
fact in the dump header.
(There are about 3.67 million pages full of page structures for
 every tera byte of system memory.  The great bulk of those
 page structures are not needed.)
Their exclusion is a makedumpfile option.

Crash will display a note during initialization if such structures
have been excluded.  Crash commands that walk page freelists, for
example, will fail. So the note will help the user understand why.

Signed-off-by: Cliff Wickman <cpw at sgi.com>
---
 defs.h     |    1 +
 diskdump.c |    3 +++
 diskdump.h |    1 +
 main.c     |   11 +++++++++++
 4 files changed, 16 insertions(+)

Index: crash-7.0.4/diskdump.c
===================================================================
--- crash-7.0.4.orig/diskdump.c
+++ crash-7.0.4/diskdump.c
@@ -749,6 +749,9 @@ restart:
 				dd->valid_pages[i]++;
 	}
 
+	if (header->status & DUMP_DH_EXCLUDED_VMEMMAP)
+		pc->flags2 |= VMEXCLUDED;
+
         return TRUE;
 
 err:
Index: crash-7.0.4/diskdump.h
===================================================================
--- crash-7.0.4.orig/diskdump.h
+++ crash-7.0.4/diskdump.h
@@ -84,6 +84,7 @@ struct kdump_sub_header {
 #define DUMP_DH_COMPRESSED_ZLIB    0x1   /* page is compressed with zlib */
 #define DUMP_DH_COMPRESSED_LZO     0x2   /* page is compressed with lzo */
 #define DUMP_DH_COMPRESSED_SNAPPY  0x4   /* page is compressed with snappy */
+#define DUMP_DH_EXCLUDED_VMEMMAP   0x8   /* unused vmemmap pages are excluded */
 
 /* descriptor of each page for vmcore */
 typedef struct page_desc {
Index: crash-7.0.4/defs.h
===================================================================
--- crash-7.0.4.orig/defs.h
+++ crash-7.0.4/defs.h
@@ -505,6 +505,7 @@ struct program_context {
 #define VMCOREINFO    (0x400ULL)
 #define ALLOW_FP      (0x800ULL)
 #define REM_PAUSED_F (0x1000ULL)
+#define VMEXCLUDED   (0x2000ULL)
 #define REMOTE_PAUSED() (pc->flags2 & REM_PAUSED_F)
 	char *cleanup;
 	char *namelist_orig;
Index: crash-7.0.4/main.c
===================================================================
--- crash-7.0.4.orig/main.c
+++ crash-7.0.4/main.c
@@ -662,6 +662,17 @@ main_loop(void)
 	} else
 		SIGACTION(SIGINT, restart, &pc->sigaction, NULL);
 
+	if (pc->flags2 & VMEXCLUDED)
+                fprintf(fp,
+        "WARNING: The vmemmap page structures that are associated with the\n"
+	"         memory pages excluded by the \"makedumpfile -d <level>\"\n"
+	"         option have been excluded from this dump.\n"
+	"         The administrator has used \"makedumpfile -e\".\n"
+	"         This will cause failures in any command that accesses a page\n"
+	"         structure of a page that is not included in the dump.  This\n"
+	"         is particularly likely when using several options of the\n"
+	"         kmem command.\n\n");
+
         /*
          *  Display system statistics and current context.
          */