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>

1 files changed, 33 insertions, 58 deletions

diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 67b847dfa2bb..df17c935d3c6 100644
--- 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;
 }