[PATCH 4/4] trace-cmd: Mount debugfs if needed for KVM data

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The KVM offset and multiplier are in the debugfs file system. If it is
not currently mounted, then try to mount it with the new tracefs API
tracefs_debug_dir() which will return the debugfs file system path, and
even mount it if possible (or NULL if it could not).

This also removes the hard coded path for /sys/kernel/debug/kvm and
removes the stat() of the directory as tracefs_debug_dir() will only
return mount locations which are directories.

Set libtracefs minimum version to 1.4 as that is what will have the
tarcefs_debug_dir() in it.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 Makefile                           |  2 +-
 lib/trace-cmd/trace-timesync-kvm.c | 47 ++++++++++++++++++++++--------
 2 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index abc4ac723db4..3452649229df 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ export LIBTRACECMD_VERSION
 VERSION_FILE = ltc_version.h
 
 LIBTRACEEVENT_MIN_VERSION = 1.5
-LIBTRACEFS_MIN_VERSION = 1.3
+LIBTRACEFS_MIN_VERSION = 1.4
 
 MAKEFLAGS += --no-print-directory
 
diff --git a/lib/trace-cmd/trace-timesync-kvm.c b/lib/trace-cmd/trace-timesync-kvm.c
index 671eafaf62b8..1db63d94f545 100644
--- a/lib/trace-cmd/trace-timesync-kvm.c
+++ b/lib/trace-cmd/trace-timesync-kvm.c
@@ -16,7 +16,6 @@
 #include "tracefs.h"
 #include "trace-tsync-local.h"
 
-#define KVM_DEBUG_FS "/sys/kernel/debug/kvm"
 #define KVM_DEBUG_OFFSET_FILE	"tsc-offset"
 #define KVM_DEBUG_SCALING_FILE	"tsc-scaling-ratio"
 #define KVM_DEBUG_FRACTION_FILE	"tsc-scaling-ratio-frac-bits"
@@ -106,6 +105,24 @@ static bool kvm_scaling_check_vm_cpu(char *vname, char *cpu)
 	return true;
 }
 
+static const char *kvm_debug_dir(void)
+{
+	const char *debugfs;
+	static char *kvm_dir;
+
+	if (kvm_dir)
+		return kvm_dir;
+
+	debugfs = tracefs_debug_dir();
+	if (!debugfs)
+		return NULL;
+
+	if (asprintf(&kvm_dir, "%s/kvm", debugfs) < 0)
+		return NULL;
+
+	return kvm_dir;
+}
+
 /*
  * Returns true if a VCPU exists with a tsc-offset file and that
  * the scaling files for ratio and fraction both exist or both
@@ -116,11 +133,16 @@ static bool kvm_scaling_check_vm_cpu(char *vname, char *cpu)
 static bool kvm_scaling_check_vm(char *name)
 {
 	struct dirent *entry;
+	const char *kvm;
 	char *vdir;
 	DIR *dir;
 	bool valid = false;
 
-	if (asprintf(&vdir, "%s/%s", KVM_DEBUG_FS, name) < 0)
+	kvm = kvm_debug_dir();
+	if (!kvm)
+		return false;
+
+	if (asprintf(&vdir, "%s/%s", kvm, name) < 0)
 		return false;
 
 	dir = opendir(vdir);
@@ -150,10 +172,15 @@ static bool kvm_scaling_check_vm(char *name)
 static bool kvm_scaling_check(void)
 {
 	struct dirent *entry;
+	const char *kvm;
 	DIR *dir;
 	bool valid = false;
 
-	dir = opendir(KVM_DEBUG_FS);
+	kvm = kvm_debug_dir();
+	if (!kvm)
+		return false;
+
+	dir = opendir(kvm);
 	if (!dir)
 		return true;
 
@@ -170,18 +197,14 @@ static bool kvm_scaling_check(void)
 
 static bool kvm_support_check(bool guest)
 {
-	struct stat st;
-	int ret;
+	const char *kvm;
 
 	/* The kvm files are only in the host so we can ignore guests */
 	if (guest)
 		return true;
 
-	ret = stat(KVM_DEBUG_FS, &st);
-	if (ret < 0)
-		return false;
-
-	if (!S_ISDIR(st.st_mode))
+	kvm = kvm_debug_dir();
+	if (!kvm)
 		return false;
 
 	return kvm_scaling_check();
@@ -242,7 +265,7 @@ static int kvm_open_debug_files(struct kvm_clock_sync *kvm, int pid)
 	DIR *dir;
 	int i;
 
-	dir = opendir(KVM_DEBUG_FS);
+	dir = opendir(kvm_debug_dir());
 	if (!dir)
 		goto error;
 	if (asprintf(&pid_str, "%d-", pid) <= 0)
@@ -251,7 +274,7 @@ static int kvm_open_debug_files(struct kvm_clock_sync *kvm, int pid)
 		if (!(entry->d_type == DT_DIR &&
 		    !strncmp(entry->d_name, pid_str, strlen(pid_str))))
 			continue;
-		asprintf(&vm_dir_str, "%s/%s", KVM_DEBUG_FS, entry->d_name);
+		asprintf(&vm_dir_str, "%s/%s", kvm_debug_dir(), entry->d_name);
 		break;
 	}
 	closedir(dir);
-- 
2.35.1