selftests/bpf: allow to define asc/desc ordering for sort specs in veristat

Allow to specify '^' at the end of stat name to designate that it should
be sorted in ascending order. Similarly, allow any of 'v', 'V', '.',
'!', or '_' suffix "symbols" to designate descending order. It's such
a zoo for descending order because there is no single intuitive symbol
that could be used (using 'v' looks pretty weird in practice), so few
symbols that are "downwards leaning or pointing" were chosen. Either
way, it shouldn't cause any troubles in practice.

This new feature allows to customize sortering order to match user's
needs.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221103055304.2904589-6-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: anakryiko

tools/testing/selftests/bpf/veristat.c

@@ -419,32 +419,65 @@ static struct stat_def {
 	[MARK_READ_MAX_LEN] = { "Max mark read length", {"max_mark_read_len", "mark_read"}, },
 };
 
+static bool parse_stat_id(const char *name, size_t len, int *id)
+{
+	int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(stat_defs); i++) {
+		struct stat_def *def = &stat_defs[i];
+
+		for (j = 0; j < ARRAY_SIZE(stat_defs[i].names); j++) {
+
+			if (!def->names[j] ||
+			    strlen(def->names[j]) != len ||
+			    strncmp(def->names[j], name, len) != 0)
+				continue;
+
+			*id = i;
+			return true;
+		}
+	}
+
+	return false;
+}
+
+static bool is_asc_sym(char c)
+{
+	return c == '^';
+}
+
+static bool is_desc_sym(char c)
+{
+	return c == 'v' || c == 'V' || c == '.' || c == '!' || c == '_';
+}
+
 static int parse_stat(const char *stat_name, struct stat_specs *specs)
 {
-	int id, i;
+	int id;
+	bool has_order = false, is_asc = false;
+	size_t len = strlen(stat_name);
 
 	if (specs->spec_cnt >= ARRAY_SIZE(specs->ids)) {
 		fprintf(stderr, "Can't specify more than %zd stats\n", ARRAY_SIZE(specs->ids));
 		return -E2BIG;
 	}
 
-	for (id = 0; id < ARRAY_SIZE(stat_defs); id++) {
-		struct stat_def *def = &stat_defs[id];
-
-		for (i = 0; i < ARRAY_SIZE(stat_defs[id].names); i++) {
-			if (!def->names[i] || strcmp(def->names[i], stat_name) != 0)
-				continue;
-
-			specs->ids[specs->spec_cnt] = id;
-			specs->asc[specs->spec_cnt] = def->asc_by_default;
-			specs->spec_cnt++;
+	if (len > 1 && (is_asc_sym(stat_name[len - 1]) || is_desc_sym(stat_name[len - 1]))) {
+		has_order = true;
+		is_asc = is_asc_sym(stat_name[len - 1]);
+		len -= 1;
+	}
 
-			return 0;
-		}
+	if (!parse_stat_id(stat_name, len, &id)) {
+		fprintf(stderr, "Unrecognized stat name '%s'\n", stat_name);
+		return -ESRCH;
 	}
 
-	fprintf(stderr, "Unrecognized stat name '%s'\n", stat_name);
-	return -ESRCH;
+	specs->ids[specs->spec_cnt] = id;
+	specs->asc[specs->spec_cnt] = has_order ? is_asc : stat_defs[id].asc_by_default;
+	specs->spec_cnt++;
+
+	return 0;
 }
 
 static int parse_stats(const char *stats_str, struct stat_specs *specs)