kdb: Revive dmesg command

The kgdb dmesg command is broken after the printk rework.  The old logic
in kdb code makes no sense in terms of current printk/logging storage
format, and KDB simply hangs forever.

This patch revives the command by switching to kmsg_dumper iterator.

The code is now much more simpler and shorter.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 67b847d..df17c93 100644 (file)
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -14,6 +14,7 @@
 #include <linux/ctype.h>
 #include <linux/string.h>
 #include <linux/kernel.h>
+#include <linux/kmsg_dump.h>
 #include <linux/reboot.h>
 #include <linux/sched.h>
 #include <linux/sysrq.h>
@@ -2040,8 +2041,15 @@ static int kdb_env(int argc, const char **argv)
  */
 static int kdb_dmesg(int argc, const char **argv)
 {
-       char *syslog_data[4], *start, *end, c = '\0', *p;
-       int diag, logging, logsize, lines = 0, adjust = 0, n;
+       int diag;
+       int logging;
+       int lines = 0;
+       int adjust = 0;
+       int n = 0;
+       int skip = 0;
+       struct kmsg_dumper dumper = { .active = 1 };
+       size_t len;
+       char buf[201];
 
        if (argc > 2)
                return KDB_ARGCOUNT;
@@ -2064,22 +2072,10 @@ static int kdb_dmesg(int argc, const char **argv)
                kdb_set(2, setargs);
        }
 
-       /* syslog_data[0,1] physical start, end+1.  syslog_data[2,3]
-        * logical start, end+1. */
-       kdb_syslog_data(syslog_data);
-       if (syslog_data[2] == syslog_data[3])
-               return 0;
-       logsize = syslog_data[1] - syslog_data[0];
-       start = syslog_data[2];
-       end = syslog_data[3];
-#define KDB_WRAP(p) (((p - syslog_data[0]) % logsize) + syslog_data[0])
-       for (n = 0, p = start; p < end; ++p) {
-               c = *KDB_WRAP(p);
-               if (c == '\n')
-                       ++n;
-       }
-       if (c != '\n')
-               ++n;
+       kmsg_dump_rewind(&dumper);
+       while (kmsg_dump_get_line(&dumper, 1, NULL, 0, NULL))
+               n++;
+
        if (lines < 0) {
                if (adjust >= n)
                        kdb_printf("buffer only contains %d lines, nothing "
@@ -2087,21 +2083,11 @@ static int kdb_dmesg(int argc, const char **argv)
                else if (adjust - lines >= n)
                        kdb_printf("buffer only contains %d lines, last %d "
                                   "lines printed\n", n, n - adjust);
-               if (adjust) {
-                       for (; start < end && adjust; ++start) {
-                               if (*KDB_WRAP(start) == '\n')
-                                       --adjust;
-                       }
-                       if (start < end)
-                               ++start;
-               }
-               for (p = start; p < end && lines; ++p) {
-                       if (*KDB_WRAP(p) == '\n')
-                               ++lines;
-               }
-               end = p;
+               skip = adjust;
+               lines = abs(lines);
        } else if (lines > 0) {
-               int skip = n - (adjust + lines);
+               skip = n - lines - adjust;
+               lines = abs(lines);
                if (adjust >= n) {
                        kdb_printf("buffer only contains %d lines, "
                                   "nothing printed\n", n);
@@ -2112,35 +2098,24 @@ static int kdb_dmesg(int argc, const char **argv)
                        kdb_printf("buffer only contains %d lines, first "
                                   "%d lines printed\n", n, lines);
                }
-               for (; start < end && skip; ++start) {
-                       if (*KDB_WRAP(start) == '\n')
-                               --skip;
-               }
-               for (p = start; p < end && lines; ++p) {
-                       if (*KDB_WRAP(p) == '\n')
-                               --lines;
-               }
-               end = p;
+       } else {
+               lines = n;
        }
-       /* Do a line at a time (max 200 chars) to reduce protocol overhead */
-       c = '\n';
-       while (start != end) {
-               char buf[201];
-               p = buf;
-               if (KDB_FLAG(CMD_INTERRUPT))
-                       return 0;
-               while (start < end && (c = *KDB_WRAP(start)) &&
-                      (p - buf) < sizeof(buf)-1) {
-                       ++start;
-                       *p++ = c;
-                       if (c == '\n')
-                               break;
+
+       if (skip >= n || skip < 0)
+               return 0;
+
+       kmsg_dump_rewind(&dumper);
+       while (kmsg_dump_get_line(&dumper, 1, buf, sizeof(buf), &len)) {
+               if (skip) {
+                       skip--;
+                       continue;
                }
-               *p = '\0';
-               kdb_printf("%s", buf);
+               if (!lines--)
+                       break;
+
+               kdb_printf("%.*s\n", (int)len - 1, buf);
        }
-       if (c != '\n')
-               kdb_printf("\n");
 
        return 0;
 }