kdb: Provide forward search at more prompt

Currently kdb allows the output of comamnds to be filtered using the
| grep feature. This is useful but does not permit the output emitted
shortly after a string match to be examined without wading through the
entire unfiltered output of the command. Such a feature is particularly
useful to navigate function traces because these traces often have a
useful trigger string *before* the point of interest.

This patch reuses the existing filtering logic to introduce a simple
forward search to kdb that can be triggered from the more prompt.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

3 files changed, 26 insertions, 5 deletions

diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index a550afb99ebe..ca13e6215537 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -680,6 +680,12 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
                         size_avail = sizeof(kdb_buffer) - len;
                         goto kdb_print_out;
                 }
+                if (kdb_grepping_flag >= KDB_GREPPING_FLAG_SEARCH)
+                        /*
+                         * This was a interactive search (using '/' at more
+                         * prompt) and it has completed. Clear the flag.
+                         */
+                        kdb_grepping_flag = 0;
                 /*
                  * at this point the string is a full line and
                  * should be printed, up to the null.
@@ -798,11 +804,23 @@ kdb_printit:
                         kdb_nextline = linecount - 1;
                         kdb_printf("\r");
                         suspend_grep = 1; /* for this recursion */
+                } else if (buf1[0] == '/' && !kdb_grepping_flag) {
+                        kdb_printf("\r");
+                        kdb_getstr(kdb_grep_string, KDB_GREP_STRLEN,
+                                   kdbgetenv("SEARCHPROMPT") ?: "search> ");
+                        *strchrnul(kdb_grep_string, '\n') = '\0';
+                        kdb_grepping_flag += KDB_GREPPING_FLAG_SEARCH;
+                        suspend_grep = 1; /* for this recursion */
                 } else if (buf1[0] && buf1[0] != '\n') {
                         /* user hit something other than enter */
                         suspend_grep = 1; /* for this recursion */
-                        kdb_printf("\nOnly 'q' or 'Q' are processed at more "
-                                   "prompt, input ignored\n");
+                        if (buf1[0] != '/')
+                                kdb_printf(
+                                    "\nOnly 'q', 'Q' or '/' are processed at "
+                                    "more prompt, input ignored\n");
+                        else
+                                kdb_printf("\n'/' cannot be used during | "
+                                           "grep filtering, input ignored\n");
                 } else if (kdb_grepping_flag) {
                         /* user hit enter */
                         suspend_grep = 1; /* for this recursion */
diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c
index 420418360b81..4121345498e0 100644
--- a/kernel/debug/kdb/kdb_main.c
+++ b/kernel/debug/kdb/kdb_main.c
@@ -50,8 +50,7 @@
 static int kdb_cmd_enabled = CONFIG_KDB_DEFAULT_ENABLE;
 module_param_named(cmd_enable, kdb_cmd_enabled, int, 0600);
 
-#define GREP_LEN 256
-char kdb_grep_string[GREP_LEN];
+char kdb_grep_string[KDB_GREP_STRLEN];
 int kdb_grepping_flag;
 EXPORT_SYMBOL(kdb_grepping_flag);
 int kdb_grep_leading;
@@ -870,7 +869,7 @@ static void parse_grep(const char *str)
         len = strlen(cp);
         if (!len)
                 return;
-        if (len >= GREP_LEN) {
+        if (len >= KDB_GREP_STRLEN) {
                 kdb_printf("search string too long\n");
                 return;
         }
@@ -1280,6 +1279,8 @@ static int kdb_local(kdb_reason_t reason, int error, struct pt_regs *regs,
                 kdb_nextline = 1;
                 KDB_STATE_CLEAR(SUPPRESS);
                 kdb_grepping_flag = 0;
+                /* ensure the old search does not leak into '/' commands */
+                kdb_grep_string[0] = '\0';
 
                 cmdbuf = cmd_cur;
                 *cmdbuf = '\0';
diff --git a/kernel/debug/kdb/kdb_private.h b/kernel/debug/kdb/kdb_private.h
index eaacd1693954..da93894db7ba 100644
--- a/kernel/debug/kdb/kdb_private.h
+++ b/kernel/debug/kdb/kdb_private.h
@@ -196,7 +196,9 @@ extern int kdb_main_loop(kdb_reason_t, kdb_reason_t,
 
 /* Miscellaneous functions and data areas */
 extern int kdb_grepping_flag;
+#define KDB_GREPPING_FLAG_SEARCH 0x8000
 extern char kdb_grep_string[];
+#define KDB_GREP_STRLEN 256
 extern int kdb_grep_leading;
 extern int kdb_grep_trailing;
 extern char *kdb_cmds[];