[PATCH] trace-cmd: Auto discover running KVM VMs using virsh

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

The "trace-cmd record -A <guest>" option, used for guest tracing,
accepts VM name as parameter. But trace-cmd needs cid of that VM, in
order to perform the tracing. The old logic searches for a process with
name "qemu-system-" and parses its command line, to get guest name to
cid relation. Using a hardcoded process name and relying on specific
process command line arguments is not reliable way.
There is no API to get VM name to cid relation, but virsh can be used
instead of the old logic. As virsh is the official user interface to
libvirt, it should be more reliable than the old approach.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---

This patch depends on patch set:
"[PATCH v3 0/2] trace-cmd: Use vsock tracing to find cids and threads"
https://lore.kernel.org/linux-trace-devel/20210513204315.1206204-1-rostedt@goodmis.org/

 tracecmd/trace-vm.c | 179 +++++++++++---------------------------------
 1 file changed, 43 insertions(+), 136 deletions(-)

diff --git a/tracecmd/trace-vm.c b/tracecmd/trace-vm.c
index d3a37eee..b3921fb0 100644
--- a/tracecmd/trace-vm.c
+++ b/tracecmd/trace-vm.c
@@ -10,6 +10,7 @@
 #include <dirent.h>
 #include <limits.h>
 #include <unistd.h>
+#include <errno.h>
 
 #include "trace-local.h"
 #include "trace-msg.h"
@@ -17,25 +18,6 @@
 static struct trace_guest *guests;
 static size_t guests_len;
 
-static int set_vcpu_pid_mapping(struct trace_guest *guest, int cpu, int pid)
-{
-	int *cpu_pid;
-	int i;
-
-	if (cpu >= guest->cpu_max) {
-		cpu_pid = realloc(guest->cpu_pid, (cpu + 1) * sizeof(int));
-		if (!cpu_pid)
-			return -1;
-		/* Handle sparse CPU numbers */
-		for (i = guest->cpu_max; i < cpu; i++)
-			cpu_pid[i] = -1;
-		guest->cpu_max = cpu + 1;
-		guest->cpu_pid = cpu_pid;
-	}
-	guest->cpu_pid[cpu] = pid;
-	return 0;
-}
-
 static struct trace_guest *get_guest_by_cid(unsigned int guest_cid)
 {
 	int i;
@@ -330,140 +312,65 @@ struct trace_guest *trace_get_guest(unsigned int cid, const char *name)
 	return guest;
 }
 
-static char *get_qemu_guest_name(char *arg)
+#define VM_CID_CMD	"virsh dumpxml"
+#define VM_CID_LINE	"<cid auto="
+#define VM_CID_ID	"address='"
+static void read_guest_cid(char *name)
 {
-	char *tok, *end = arg;
-
-	while ((tok = strsep(&end, ","))) {
-		if (strncmp(tok, "guest=", 6) == 0)
-			return tok + 6;
-	}
-
-	return arg;
-}
-
-static int read_qemu_guests_pids(char *guest_task, struct trace_guest *guest)
-{
-	struct dirent *entry;
-	char path[PATH_MAX];
-	char *buf = NULL;
-	size_t n = 0;
-	int ret = 0;
-	long vcpu;
-	long pid;
-	DIR *dir;
+	struct trace_guest *guest;
+	char *cmd = NULL;
+	char line[512];
+	char *cid;
+	unsigned int cid_id = 0;
 	FILE *f;
 
-	snprintf(path, sizeof(path), "/proc/%s/task", guest_task);
-	dir = opendir(path);
-	if (!dir)
-		return -1;
+	asprintf(&cmd, "%s %s", VM_CID_CMD, name);
+	f = popen(cmd, "r");
+	free(cmd);
+	if (f == NULL)
+		return;
 
-	while (!ret && (entry = readdir(dir))) {
-		if (!(entry->d_type == DT_DIR && is_digits(entry->d_name)))
+	while (fgets(line, sizeof(line), f) != NULL) {
+		if (!strstr(line, VM_CID_LINE))
 			continue;
-
-		snprintf(path, sizeof(path), "/proc/%s/task/%s/comm",
-			 guest_task, entry->d_name);
-		f = fopen(path, "r");
-		if (!f)
+		cid = strstr(line, VM_CID_ID);
+		if (!cid)
 			continue;
-
-		if (getline(&buf, &n, f) >= 0 &&
-		    strncmp(buf, "CPU ", 4) == 0) {
-			vcpu = strtol(buf + 4, NULL, 10);
-			pid = strtol(entry->d_name, NULL, 10);
-			if (vcpu < INT_MAX && pid < INT_MAX &&
-			    vcpu >= 0 && pid >= 0) {
-				if (set_vcpu_pid_mapping(guest, vcpu, pid))
-					ret = -1;
-			}
-		}
-
-		fclose(f);
+		cid_id = strtol(cid + strlen(VM_CID_ID), NULL, 10);
+		if ((cid_id == LONG_MIN || cid_id == LONG_MAX) && errno == ERANGE)
+			continue;
+		guest = add_guest(cid_id, name);
+		if (guest)
+			find_pid_by_cid(guest);
+		break;
 	}
-	free(buf);
-	return ret;
+
+	/* close */
+	pclose(f);
 }
 
+#define VM_NAME_CMD	"virsh list --name"
 void read_qemu_guests(void)
 {
-	static bool initialized;
-	struct dirent *entry;
-	char path[PATH_MAX];
-	DIR *dir;
+	char name[256];
+	FILE *f;
 
-	if (initialized)
+	f = popen(VM_NAME_CMD, "r");
+	if (f == NULL) {
+		die("Failed to get VM names\n");
 		return;
+	}
 
-	initialized = true;
-	dir = opendir("/proc");
-	if (!dir)
-		die("Can not open /proc");
-
-	while ((entry = readdir(dir))) {
-		bool is_qemu = false, last_was_name = false;
-		struct trace_guest guest = {};
-		char *p, *arg = NULL;
-		size_t arg_size = 0;
-		FILE *f;
-
-		if (!(entry->d_type == DT_DIR && is_digits(entry->d_name)))
-			continue;
-
-		guest.pid = atoi(entry->d_name);
-		snprintf(path, sizeof(path), "/proc/%s/cmdline", entry->d_name);
-		f = fopen(path, "r");
-		if (!f)
+	while (fgets(name, sizeof(name), f) != NULL) {
+		if (name[0] == '\n')
 			continue;
-
-		while (getdelim(&arg, &arg_size, 0, f) != -1) {
-			if (!is_qemu && strstr(arg, "qemu-system-")) {
-				is_qemu = true;
-				continue;
-			}
-
-			if (!is_qemu)
-				continue;
-
-			if (strcmp(arg, "-name") == 0) {
-				last_was_name = true;
-				continue;
-			}
-
-			if (last_was_name) {
-				guest.name = strdup(get_qemu_guest_name(arg));
-				if (!guest.name)
-					die("allocating guest name");
-				last_was_name = false;
-				continue;
-			}
-
-			p = strstr(arg, "guest-cid=");
-			if (p) {
-				guest.cid = atoi(p + 10);
-				continue;
-			}
-		}
-
-		if (!is_qemu)
-			goto next;
-
-		if (read_qemu_guests_pids(entry->d_name, &guest))
-			warning("Failed to retrieve VPCU - PID mapping for guest %s",
-					guest.name ? guest.name : "Unknown");
-
-		guests = realloc(guests, (guests_len + 1) * sizeof(*guests));
-		if (!guests)
-			die("Can not allocate guest buffer");
-		guests[guests_len++] = guest;
-
-next:
-		free(arg);
-		fclose(f);
+		if (name[strlen(name) - 1] == '\n')
+			name[strlen(name) - 1] = '\0';
+		read_guest_cid(name);
 	}
 
-	closedir(dir);
+	/* close */
+	pclose(f);
 }
 
 int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu)
-- 
2.31.1