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>

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 @@ int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
 			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 */

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';

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[];