tools lib fs: Add helper to find mounted file systems

In preparation for adding tracefs for perf to use, create a findfs
helper utility that find_debugfs uses instead of hard coding the search
in the code. This will allow for a find_tracefs to be used as well.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20150202193552.735023362@goodmis.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/api/Makefile

@@ -9,11 +9,13 @@ LIB_H=
 LIB_OBJS=
 
 LIB_H += fs/debugfs.h
+LIB_H += fs/findfs.h
 LIB_H += fs/fs.h
 # See comment below about piggybacking...
 LIB_H += fd/array.h
 
 LIB_OBJS += $(OUTPUT)fs/debugfs.o
+LIB_OBJS += $(OUTPUT)fs/findfs.o
 LIB_OBJS += $(OUTPUT)fs/fs.o
 # XXX piggybacking here, need to introduce libapikfd, or rename this
 # to plain libapik.a and make it have it all api goodies

tools/lib/api/fs/debugfs.c

@@ -20,58 +20,21 @@ static const char * const debugfs_known_mountpoints[] = {
 
 static bool debugfs_found;
 
-/* verify that a mountpoint is actually a debugfs instance */
-
-static int debugfs_valid_mountpoint(const char *debugfs)
-{
-	struct statfs st_fs;
-
-	if (statfs(debugfs, &st_fs) < 0)
-		return -ENOENT;
-	else if ((long)st_fs.f_type != (long)DEBUGFS_MAGIC)
-		return -ENOENT;
-
-	return 0;
-}
-
 /* find the path to the mounted debugfs */
 const char *debugfs_find_mountpoint(void)
 {
-	const char * const *ptr;
-	char type[100];
-	FILE *fp;
+	const char *ret;
 
 	if (debugfs_found)
 		return (const char *)debugfs_mountpoint;
 
-	ptr = debugfs_known_mountpoints;
-	while (*ptr) {
-		if (debugfs_valid_mountpoint(*ptr) == 0) {
-			debugfs_found = true;
-			strcpy(debugfs_mountpoint, *ptr);
-			return debugfs_mountpoint;
-		}
-		ptr++;
-	}
+	ret = find_mountpoint("debugfs", (long) DEBUGFS_MAGIC,
+			      debugfs_mountpoint, PATH_MAX + 1,
+			      debugfs_known_mountpoints);
+	if (ret)
+		debugfs_found = true;
 
-	/* give up and parse /proc/mounts */
-	fp = fopen("/proc/mounts", "r");
-	if (fp == NULL)
-		return NULL;
-
-	while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
-		      debugfs_mountpoint, type) == 2) {
-		if (strcmp(type, "debugfs") == 0)
-			break;
-	}
-	fclose(fp);
-
-	if (strcmp(type, "debugfs") != 0)
-		return NULL;
-
-	debugfs_found = true;
-
-	return debugfs_mountpoint;
+	return ret;
 }
 
 /* mount the debugfs somewhere if it's not mounted */

tools/lib/api/fs/debugfs.h

@@ -1,16 +1,7 @@
 #ifndef __API_DEBUGFS_H__
 #define __API_DEBUGFS_H__
 
-#define _STR(x) #x
-#define STR(x) _STR(x)
-
-/*
- * On most systems <limits.h> would have given us this, but  not on some systems
- * (e.g. GNU/Hurd).
- */
-#ifndef PATH_MAX
-#define PATH_MAX 4096
-#endif
+#include "findfs.h"
 
 #ifndef DEBUGFS_MAGIC
 #define DEBUGFS_MAGIC          0x64626720

tools/lib/api/fs/findfs.c

@@ -0,0 +1,63 @@
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <sys/vfs.h>
+
+#include "findfs.h"
+
+/* verify that a mountpoint is actually the type we want */
+
+int valid_mountpoint(const char *mount, long magic)
+{
+	struct statfs st_fs;
+
+	if (statfs(mount, &st_fs) < 0)
+		return -ENOENT;
+	else if ((long)st_fs.f_type != magic)
+		return -ENOENT;
+
+	return 0;
+}
+
+/* find the path to a mounted file system */
+const char *find_mountpoint(const char *fstype, long magic,
+			    char *mountpoint, int len,
+			    const char * const *known_mountpoints)
+{
+	const char * const *ptr;
+	char format[128];
+	char type[100];
+	FILE *fp;
+
+	if (known_mountpoints) {
+		ptr = known_mountpoints;
+		while (*ptr) {
+			if (valid_mountpoint(*ptr, magic) == 0) {
+				strncpy(mountpoint, *ptr, len - 1);
+				mountpoint[len-1] = 0;
+				return mountpoint;
+			}
+			ptr++;
+		}
+	}
+
+	/* give up and parse /proc/mounts */
+	fp = fopen("/proc/mounts", "r");
+	if (fp == NULL)
+		return NULL;
+
+	snprintf(format, 128, "%%*s %%%ds %%99s %%*s %%*d %%*d\n", len);
+
+	while (fscanf(fp, format, mountpoint, type) == 2) {
+		if (strcmp(type, fstype) == 0)
+			break;
+	}
+	fclose(fp);
+
+	if (strcmp(type, fstype) != 0)
+		return NULL;
+
+	return mountpoint;
+}

tools/lib/api/fs/findfs.h

@@ -0,0 +1,21 @@
+#ifndef __API_FINDFS_H__
+#define __API_FINDFS_H__
+
+#define _STR(x) #x
+#define STR(x) _STR(x)
+
+/*
+ * On most systems <limits.h> would have given us this, but  not on some systems
+ * (e.g. GNU/Hurd).
+ */
+#ifndef PATH_MAX
+#define PATH_MAX 4096
+#endif
+
+const char *find_mountpoint(const char *fstype, long magic,
+			    char *mountpoint, int len,
+			    const char * const *known_mountpoints);
+
+int valid_mountpoint(const char *mount, long magic);
+
+#endif /* __API_FINDFS_H__ */