[Crash-utility] [PATCH v2 5/5] diskdump: Warn on incomplete dumps

[Roman Bolshakov]

crash warns that ELF dump is incomplete like this:

  WARNING: vmcore: may be truncated or incomplete
           PT_LOAD p_offset: 218960740
                   p_filesz: 4194304
             bytes required: 223155044
              dumpfile size: 219960740

The warning saves a lot of time when figuring out what went wrong, but
crash misses explicit dump detection for compressed kdumps.

The change adds the warning for compressed kdumps:

  WARNING: vmcore: may be truncated or incomplete
                data_offset: 262144
                 block_size: 65536
          total_valid_pages: 2438
             first_empty_pd: 100
             bytes required: 157467661
              dumpfile size: 265982

bytes required is computed as:

	data_offset (kdump header + bitmaps)
            +
        total_valid_pages * page descriptor size (page descriptors)
            +
        zero page (that immediately follows page descriptors)
            +
        compressed size of every present page in the list of valid pages
            +
        block_size for every incomplete page (i.e page descriptor has
        zero offset)

The warning is also printed for incomplete split dumps.

Signed-off-by: Roman Bolshakov <r.bolshakov at yadro.com>
---
 diskdump.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 69 insertions(+), 2 deletions(-)

diff --git a/diskdump.c b/diskdump.c
index de3eeb2..5151db1 100644
--- a/diskdump.c
+++ b/diskdump.c
@@ -23,6 +23,8 @@
  * GNU General Public License for more details.
  */
 
+#define _LARGEFILE64_SOURCE 1  /* stat64() */
+
 #include "defs.h"
 #include "diskdump.h"
 #include "xen_dom0.h"
@@ -548,6 +550,12 @@ read_dump_header(char *file)
 	ulong pfn;
 	int i, j, max_sect_len;
 	int is_split = 0;
+	struct stat64 stat;
+	page_desc_t pd;
+	ulong page_idx;
+	int first_empty_pd = 0;
+	int zero_page_counted = 0;
+	size_t expected_size = 0;
 
 	if (block_size < 0)
 		return FALSE;
@@ -898,13 +906,72 @@ restart:
 		pfn = start;
 	}
 
+	expected_size = dd->data_offset;
 	dd->valid_pages = calloc(sizeof(ulong), max_sect_len + 1);
 	dd->max_sect_len = max_sect_len;
 	for (i = 1; i < max_sect_len + 1; i++) {
 		dd->valid_pages[i] = dd->valid_pages[i - 1];
 		for (j = 0; j < BITMAP_SECT_LEN; j++, pfn++)
-			if (page_is_dumpable(pfn))
-				dd->valid_pages[i]++;
+			if (page_is_dumpable(pfn)) {
+				page_idx = dd->valid_pages[i]++;
+
+				offset = dd->data_offset +
+					 page_idx * sizeof(pd);
+
+				if (read_pd(dd->dfd, offset, &pd)) {
+					/*
+					 * Truncated page descriptor at most
+					 * references full page.
+					 */
+					expected_size += block_size;
+					goto next;
+				}
+
+				if (pd.offset == 0) {
+					if (!first_empty_pd)
+						first_empty_pd = page_idx;
+					/*
+					 * Incomplete pages at most use the
+					 * whole page.
+					 */
+					expected_size += block_size;
+				} else if (!pd.flags) {
+					/*
+					 * Zero page has no compression flags.
+					 */
+					if (!zero_page_counted) {
+						expected_size += block_size;
+						zero_page_counted = 1;
+					}
+				} else if (pd.flags) {
+					/* Regular compressed page */
+					expected_size += pd.size;
+				}
+
+next:
+				expected_size += sizeof(pd);
+			}
+	}
+
+	if (stat64(dd->filename, &stat) < 0) {
+		error(INFO, "%s: cannot stat %s\n",
+		      DISKDUMP_VALID() ? "diskdump" : "compressed kdump",
+		      dd->filename);
+		goto err;
+	}
+
+	if (expected_size > stat.st_size || first_empty_pd) {
+		error(WARNING,
+		      "%s: may be truncated or incomplete\n"
+		      "              data_offset: %lld\n"
+		      "               block_size: %lld\n"
+		      "        total_valid_pages: %lld\n"
+		      "           first_empty_pd: %lld\n"
+		      "           bytes required: %lld\n"
+		      "            dumpfile size: %lld\n\n",
+		      dd->filename, dd->data_offset,
+		      dd->block_size, dd->valid_pages[dd->max_sect_len],
+		      first_empty_pd, expected_size, stat.st_size);
 	}
 
         return TRUE;
-- 
2.32.0