perf pmu: Parse sysfs events directly from a file

Rather than read a sysfs events file into a 256 byte char buffer, pass
the FILE* directly to the lex/yacc parser.

This avoids there being a maximum events file size.

While changing the API, constify some arguments to remove unnecessary
casts.

Allocating the read buffer decreases the performance of pmu-scan by
around 3%.

Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230824041330.266337-10-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/arch/x86/util/intel-pt.c

@@ -74,7 +74,7 @@ static int intel_pt_parse_terms_with_default(struct perf_pmu *pmu,
 
 	INIT_LIST_HEAD(terms);
 
-	err = parse_events_terms(terms, str);
+	err = parse_events_terms(terms, str, /*input=*/ NULL);
 	if (err)
 		goto out_free;
 

tools/perf/tests/parse-events.c

@@ -2472,7 +2472,7 @@ static int test_term(const struct terms_test *t)
 
 	INIT_LIST_HEAD(&terms);
 
-	ret = parse_events_terms(&terms, t->str);
+	ret = parse_events_terms(&terms, t->str, /*input=*/ NULL);
 	if (ret) {
 		pr_debug("failed to parse terms '%s', err %d\n",
 			 t->str , ret);

tools/perf/util/parse-events.c

@@ -1715,6 +1715,7 @@ int parse_events_name(struct list_head *list, const char *name)
 }
 
 static int parse_events__scanner(const char *str,
+				 FILE *input,
 				 struct parse_events_state *parse_state)
 {
 	YY_BUFFER_STATE buffer;
@@ -1725,32 +1726,37 @@ static int parse_events__scanner(const char *str,
 	if (ret)
 		return ret;
 
-	buffer = parse_events__scan_string(str, scanner);
+	if (str)
+		buffer = parse_events__scan_string(str, scanner);
+	else
+	        parse_events_set_in(input, scanner);
 
 #ifdef PARSER_DEBUG
 	parse_events_debug = 1;
 	parse_events_set_debug(1, scanner);
 #endif
 	ret = parse_events_parse(parse_state, scanner);
 
-	parse_events__flush_buffer(buffer, scanner);
-	parse_events__delete_buffer(buffer, scanner);
+	if (str) {
+		parse_events__flush_buffer(buffer, scanner);
+		parse_events__delete_buffer(buffer, scanner);
+	}
 	parse_events_lex_destroy(scanner);
 	return ret;
 }
 
 /*
  * parse event config string, return a list of event terms.
  */
-int parse_events_terms(struct list_head *terms, const char *str)
+int parse_events_terms(struct list_head *terms, const char *str, FILE *input)
 {
 	struct parse_events_state parse_state = {
 		.terms  = NULL,
 		.stoken = PE_START_TERMS,
 	};
 	int ret;
 
-	ret = parse_events__scanner(str, &parse_state);
+	ret = parse_events__scanner(str, input, &parse_state);
 
 	if (!ret) {
 		list_splice(parse_state.terms, terms);
@@ -2001,7 +2007,7 @@ int __parse_events(struct evlist *evlist, const char *str, const char *pmu_filte
 	};
 	int ret, ret2;
 
-	ret = parse_events__scanner(str, &parse_state);
+	ret = parse_events__scanner(str, /*input=*/ NULL, &parse_state);
 
 	if (!ret && list_empty(&parse_state.list)) {
 		WARN_ONCE(true, "WARNING: event parser found nothing\n");

tools/perf/util/parse-events.h

@@ -9,6 +9,7 @@
 #include <stdbool.h>
 #include <linux/types.h>
 #include <linux/perf_event.h>
+#include <stdio.h>
 #include <string.h>
 
 struct evsel;
@@ -42,7 +43,7 @@ static inline int parse_events(struct evlist *evlist, const char *str,
 
 int parse_event(struct evlist *evlist, const char *str);
 
-int parse_events_terms(struct list_head *terms, const char *str);
+int parse_events_terms(struct list_head *terms, const char *str, FILE *input);
 int parse_filter(const struct option *opt, const char *str, int unset);
 int exclude_perf(const struct option *opt, const char *arg, int unset);
 

tools/perf/util/pmu.c

@@ -280,7 +280,7 @@ int perf_pmu__convert_scale(const char *scale, char **end, double *sval)
 	return ret;
 }
 
-static int perf_pmu__parse_scale(struct perf_pmu_alias *alias, int dirfd, char *name)
+static int perf_pmu__parse_scale(struct perf_pmu_alias *alias, int dirfd, const char *name)
 {
 	struct stat st;
 	ssize_t sret;
@@ -312,7 +312,7 @@ static int perf_pmu__parse_scale(struct perf_pmu_alias *alias, int dirfd, char *
 	return ret;
 }
 
-static int perf_pmu__parse_unit(struct perf_pmu_alias *alias, int dirfd, char *name)
+static int perf_pmu__parse_unit(struct perf_pmu_alias *alias, int dirfd, const char *name)
 {
 	char path[PATH_MAX];
 	ssize_t sret;
@@ -343,7 +343,7 @@ static int perf_pmu__parse_unit(struct perf_pmu_alias *alias, int dirfd, char *n
 }
 
 static int
-perf_pmu__parse_per_pkg(struct perf_pmu_alias *alias, int dirfd, char *name)
+perf_pmu__parse_per_pkg(struct perf_pmu_alias *alias, int dirfd, const char *name)
 {
 	char path[PATH_MAX];
 	int fd;
@@ -361,7 +361,7 @@ perf_pmu__parse_per_pkg(struct perf_pmu_alias *alias, int dirfd, char *name)
 }
 
 static int perf_pmu__parse_snapshot(struct perf_pmu_alias *alias,
-				    int dirfd, char *name)
+				    int dirfd, const char *name)
 {
 	char path[PATH_MAX];
 	int fd;
@@ -454,8 +454,9 @@ static bool perf_pmu_merge_alias(struct perf_pmu_alias *newalias,
 	return false;
 }
 
-static int __perf_pmu__new_alias(struct list_head *list, int dirfd, char *name,
-				 char *desc, char *val, const struct pmu_event *pe)
+static int perf_pmu__new_alias(struct list_head *list, int dirfd, const char *name,
+				const char *desc, const char *val, FILE *val_fd,
+				const struct pmu_event *pe)
 {
 	struct parse_events_term *term;
 	struct perf_pmu_alias *alias;
@@ -484,7 +485,7 @@ static int __perf_pmu__new_alias(struct list_head *list, int dirfd, char *name,
 	alias->snapshot = false;
 	alias->deprecated = deprecated;
 
-	ret = parse_events_terms(&alias->terms, val);
+	ret = parse_events_terms(&alias->terms, val, val_fd);
 	if (ret) {
 		pr_err("Cannot parse alias %s: %d\n", val, ret);
 		free(alias);
@@ -541,23 +542,6 @@ static int __perf_pmu__new_alias(struct list_head *list, int dirfd, char *name,
 	return 0;
 }
 
-static int perf_pmu__new_alias(struct list_head *list, int dirfd, char *name, FILE *file)
-{
-	char buf[256];
-	int ret;
-
-	ret = fread(buf, 1, sizeof(buf), file);
-	if (ret == 0)
-		return -EINVAL;
-
-	buf[ret] = 0;
-
-	/* Remove trailing newline from sysfs file */
-	strim(buf);
-
-	return __perf_pmu__new_alias(list, dirfd, name, NULL, buf, NULL);
-}
-
 static inline bool pmu_alias_info_file(char *name)
 {
 	size_t len;
@@ -613,7 +597,8 @@ static int pmu_aliases_parse(int dirfd, struct list_head *head)
 			continue;
 		}
 
-		if (perf_pmu__new_alias(head, dirfd, name, file) < 0)
+		if (perf_pmu__new_alias(head, dirfd, name, /*desc=*/ NULL,
+					/*val=*/ NULL, file, /*pe=*/ NULL) < 0)
 			pr_debug("Cannot set up %s\n", name);
 		fclose(file);
 	}
@@ -866,7 +851,7 @@ static int pmu_add_cpu_aliases_map_callback(const struct pmu_event *pe,
 	struct list_head *head = vdata;
 
 	/* need type casts to override 'const' */
-	__perf_pmu__new_alias(head, -1, (char *)pe->name, (char *)pe->desc, (char *)pe->event, pe);
+	perf_pmu__new_alias(head, -1, pe->name, pe->desc, pe->event, /*val_fd=*/ NULL, pe);
 	return 0;
 }
 
@@ -907,11 +892,12 @@ static int pmu_add_sys_aliases_iter_fn(const struct pmu_event *pe,
 
 	if (!strcmp(pmu->id, pe->compat) &&
 	    pmu_uncore_alias_match(pe->pmu, pmu->name)) {
-		__perf_pmu__new_alias(idata->head, -1,
-				      (char *)pe->name,
-				      (char *)pe->desc,
-				      (char *)pe->event,
-				      pe);
+		perf_pmu__new_alias(idata->head, -1,
+				pe->name,
+				pe->desc,
+				pe->event,
+				/*val_fd=*/ NULL,
+				pe);
 	}
 
 	return 0;