qga: determine default state dir and pidfile dynamically

No effective change on POSIX, but on Win32 the defaults come from the
environment / session.

Since commit 39097daf ("qemu-ga: use key-value store to avoid recycling fd
handles after restart") we've relied on the state directory for the fd
handles' key-value store. Even though we don't support the guest-file-*
commands on win32 yet, the key-value store is written, and it's the first
use of the state directory on win32. We should have a sensible default for
its location.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/main.c

@@ -45,16 +45,21 @@
 
 #ifndef _WIN32
 #define QGA_VIRTIO_PATH_DEFAULT "/dev/virtio-ports/org.qemu.guest_agent.0"
+#define QGA_STATE_RELATIVE_DIR  "run"
 #else
 #define QGA_VIRTIO_PATH_DEFAULT "\\\\.\\Global\\org.qemu.guest_agent.0"
+#define QGA_STATE_RELATIVE_DIR  "qemu-ga"
 #endif
-#define QGA_STATEDIR_DEFAULT CONFIG_QEMU_LOCALSTATEDIR "/run"
-#define QGA_PIDFILE_DEFAULT QGA_STATEDIR_DEFAULT "/qemu-ga.pid"
 #ifdef CONFIG_FSFREEZE
 #define QGA_FSFREEZE_HOOK_DEFAULT CONFIG_QEMU_CONFDIR "/fsfreeze-hook"
 #endif
 #define QGA_SENTINEL_BYTE 0xFF
 
+static struct {
+    const char *state_dir;
+    const char *pidfile;
+} dfl_pathnames;
+
 typedef struct GAPersistentState {
 #define QGA_PSTATE_DEFAULT_FD_COUNTER 1000
     int64_t fd_counter;
@@ -106,6 +111,17 @@ DWORD WINAPI service_ctrl_handler(DWORD ctrl, DWORD type, LPVOID data,
 VOID WINAPI service_main(DWORD argc, TCHAR *argv[]);
 #endif
 
+static void
+init_dfl_pathnames(void)
+{
+    g_assert(dfl_pathnames.state_dir == NULL);
+    g_assert(dfl_pathnames.pidfile == NULL);
+    dfl_pathnames.state_dir = qemu_get_local_state_pathname(
+      QGA_STATE_RELATIVE_DIR);
+    dfl_pathnames.pidfile   = qemu_get_local_state_pathname(
+      QGA_STATE_RELATIVE_DIR G_DIR_SEPARATOR_S "qemu-ga.pid");
+}
+
 static void quit_handler(int sig)
 {
     /* if we're frozen, don't exit unless we're absolutely forced to,
@@ -198,11 +214,11 @@ static void usage(const char *cmd)
 "  -h, --help        display this help and exit\n"
 "\n"
 "Report bugs to <mdroth@linux.vnet.ibm.com>\n"
-    , cmd, QEMU_VERSION, QGA_VIRTIO_PATH_DEFAULT, QGA_PIDFILE_DEFAULT,
+    , cmd, QEMU_VERSION, QGA_VIRTIO_PATH_DEFAULT, dfl_pathnames.pidfile,
 #ifdef CONFIG_FSFREEZE
     QGA_FSFREEZE_HOOK_DEFAULT,
 #endif
-    QGA_STATEDIR_DEFAULT);
+    dfl_pathnames.state_dir);
 }
 
 static const char *ga_log_level_str(GLogLevelFlags level)
@@ -908,11 +924,11 @@ int main(int argc, char **argv)
     const char *sopt = "hVvdm:p:l:f:F::b:s:t:";
     const char *method = NULL, *path = NULL;
     const char *log_filepath = NULL;
-    const char *pid_filepath = QGA_PIDFILE_DEFAULT;
+    const char *pid_filepath;
 #ifdef CONFIG_FSFREEZE
     const char *fsfreeze_hook = NULL;
 #endif
-    const char *state_dir = QGA_STATEDIR_DEFAULT;
+    const char *state_dir;
 #ifdef _WIN32
     const char *service = NULL;
 #endif
@@ -942,6 +958,10 @@ int main(int argc, char **argv)
 
     module_call_init(MODULE_INIT_QAPI);
 
+    init_dfl_pathnames();
+    pid_filepath = dfl_pathnames.pidfile;
+    state_dir = dfl_pathnames.state_dir;
+
     while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
         switch (ch) {
         case 'm':