perf tools: Add debugfs utility routines for perf

Add routines to locate the debugfs mount point and to manage the
mounting and unmounting of the debugfs.
Signed-off-by: Clark Williams <williams@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091101155621.2b3503ee@torg>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/Makefile

@@ -353,6 +353,7 @@ LIB_H += util/include/asm/swab.h
 LIB_H += util/include/asm/system.h
 LIB_H += util/include/asm/uaccess.h
 LIB_H += perf.h
+LIB_H += util/debugfs.h
 LIB_H += util/event.h
 LIB_H += util/types.h
 LIB_H += util/levenshtein.h
@@ -378,6 +379,7 @@ LIB_OBJS += util/abspath.o
 LIB_OBJS += util/alias.o
 LIB_OBJS += util/config.o
 LIB_OBJS += util/ctype.o
+LIB_OBJS += util/debugfs.o
 LIB_OBJS += util/environment.o
 LIB_OBJS += util/event.o
 LIB_OBJS += util/exec_cmd.o

tools/perf/util/debugfs.c

+#include "util.h"
+#include "debugfs.h"
+#include "cache.h"
+
+static int debugfs_premounted;
+static char debugfs_mountpoint[MAX_PATH+1];
+
+static const char *debugfs_known_mountpoints[] = {
+	"/sys/kernel/debug/",
+	"/debug/",
+	0,
+};
+
+/* use this to force a umount */
+void debugfs_force_cleanup(void)
+{
+	debugfs_find_mountpoint();
+	debugfs_premounted = 0;
+	debugfs_umount();
+}
+
+/* construct a full path to a debugfs element */
+int debugfs_make_path(const char *element, char *buffer, int size)
+{
+	int len;
+
+	if (strlen(debugfs_mountpoint) == 0) {
+		buffer[0] = '\0';
+		return -1;
+	}
+
+	len = strlen(debugfs_mountpoint) + strlen(element) + 1;
+	if (len >= size)
+		return len+1;
+
+	snprintf(buffer, size-1, "%s/%s", debugfs_mountpoint, element);
+	return 0;
+}
+
+static int debugfs_found;
+
+/* find the path to the mounted debugfs */
+const char *debugfs_find_mountpoint(void)
+{
+	const char **ptr;
+	char type[100];
+	FILE *fp;
+
+	if (debugfs_found)
+		return (const char *) debugfs_mountpoint;
+
+	ptr = debugfs_known_mountpoints;
+	while (*ptr) {
+		if (debugfs_valid_mountpoint(*ptr) == 0) {
+			debugfs_found = 1;
+			strcpy(debugfs_mountpoint, *ptr);
+			return debugfs_mountpoint;
+		}
+		ptr++;
+	}
+
+	/* give up and parse /proc/mounts */
+	fp = fopen("/proc/mounts", "r");
+	if (fp == NULL)
+		die("Can't open /proc/mounts for read");
+
+	while (fscanf(fp, "%*s %"
+		      STR(MAX_PATH)
+		      "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 = 1;
+
+	return debugfs_mountpoint;
+}
+
+/* verify that a mountpoint is actually a debugfs instance */
+
+int debugfs_valid_mountpoint(const char *debugfs)
+{
+	struct statfs st_fs;
+
+	if (statfs(debugfs, &st_fs) < 0)
+		return -ENOENT;
+	else if (st_fs.f_type != (long) DEBUGFS_MAGIC)
+		return -ENOENT;
+
+	return 0;
+}
+
+
+int debugfs_valid_entry(const char *path)
+{
+	struct stat st;
+
+	if (stat(path, &st))
+		return -errno;
+
+	return 0;
+}
+
+/* mount the debugfs somewhere */
+
+int debugfs_mount(const char *mountpoint)
+{
+	char mountcmd[128];
+
+	/* see if it's already mounted */
+	if (debugfs_find_mountpoint()) {
+		debugfs_premounted = 1;
+		return 0;
+	}
+
+	/* if not mounted and no argument */
+	if (mountpoint == NULL) {
+		/* see if environment variable set */
+		mountpoint = getenv(PERF_DEBUGFS_ENVIRONMENT);
+		/* if no environment variable, use default */
+		if (mountpoint == NULL)
+			mountpoint = "/sys/kernel/debug";
+	}
+
+	/* save the mountpoint */
+	strncpy(debugfs_mountpoint, mountpoint, sizeof(debugfs_mountpoint));
+
+	/* mount it */
+	snprintf(mountcmd, sizeof(mountcmd),
+		 "/bin/mount -t debugfs debugfs %s", mountpoint);
+	return system(mountcmd);
+}
+
+/* umount the debugfs */
+
+int debugfs_umount(void)
+{
+	char umountcmd[128];
+	int ret;
+
+	/* if it was already mounted, leave it */
+	if (debugfs_premounted)
+		return 0;
+
+	/* make sure it's a valid mount point */
+	ret = debugfs_valid_mountpoint(debugfs_mountpoint);
+	if (ret)
+		return ret;
+
+	snprintf(umountcmd, sizeof(umountcmd),
+		 "/bin/umount %s", debugfs_mountpoint);
+	return system(umountcmd);
+}
+
+int debugfs_write(const char *entry, const char *value)
+{
+	char path[MAX_PATH+1];
+	int ret, count;
+	int fd;
+
+	/* construct the path */
+	snprintf(path, sizeof(path), "%s/%s", debugfs_mountpoint, entry);
+
+	/* verify that it exists */
+	ret = debugfs_valid_entry(path);
+	if (ret)
+		return ret;
+
+	/* get how many chars we're going to write */
+	count = strlen(value);
+
+	/* open the debugfs entry */
+	fd = open(path, O_RDWR);
+	if (fd < 0)
+		return -errno;
+
+	while (count > 0) {
+		/* write it */
+		ret = write(fd, value, count);
+		if (ret <= 0) {
+			if (ret == EAGAIN)
+				continue;
+			close(fd);
+			return -errno;
+		}
+		count -= ret;
+	}
+
+	/* close it */
+	close(fd);
+
+	/* return success */
+	return 0;
+}
+
+/*
+ * read a debugfs entry
+ * returns the number of chars read or a negative errno
+ */
+int debugfs_read(const char *entry, char *buffer, size_t size)
+{
+	char path[MAX_PATH+1];
+	int ret;
+	int fd;
+
+	/* construct the path */
+	snprintf(path, sizeof(path), "%s/%s", debugfs_mountpoint, entry);
+
+	/* verify that it exists */
+	ret = debugfs_valid_entry(path);
+	if (ret)
+		return ret;
+
+	/* open the debugfs entry */
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return -errno;
+
+	do {
+		/* read it */
+		ret = read(fd, buffer, size);
+		if (ret == 0) {
+			close(fd);
+			return EOF;
+		}
+	} while (ret < 0 && errno == EAGAIN);
+
+	/* close it */
+	close(fd);
+
+	/* make *sure* there's a null character at the end */
+	buffer[ret] = '\0';
+
+	/* return the number of chars read */
+	return ret;
+}

tools/perf/util/debugfs.h

+#ifndef __DEBUGFS_H__
+#define __DEBUGFS_H__
+
+#include <sys/mount.h>
+
+#ifndef MAX_PATH
+# define MAX_PATH 256
+#endif
+
+#ifndef STR
+# define _STR(x) #x
+# define STR(x) _STR(x)
+#endif
+
+extern const char *debugfs_find_mountpoint(void);
+extern int debugfs_valid_mountpoint(const char *debugfs);
+extern int debugfs_valid_entry(const char *path);
+extern int debugfs_mount(const char *mountpoint);
+extern int debugfs_umount(void);
+extern int debugfs_write(const char *entry, const char *value);
+extern int debugfs_read(const char *entry, char *buffer, size_t size);
+extern void debugfs_force_cleanup(void);
+extern int debugfs_make_path(const char *element, char *buffer, int size);
+
+#endif /* __DEBUGFS_H__ */