[PATCH v3 21/22] qga: allow configuration file path via the cli

["Daniel P. Berrangé" <berrange@redhat.com>]

Allowing the user to set the QGA_CONF environment variable to change
the default configuration file path is very unusual practice, made
more obscure since this ability is not documented.

This introduces the more normal '-c PATH'  / '--config=PATH' command
line argument approach. This requires that we parse the comamnd line
twice, since we want the command line arguments to take priority over
the configuration file settings in general.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 docs/interop/qemu-ga.rst |  5 +++++
 qga/main.c               | 43 ++++++++++++++++++++++++++++++----------
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/docs/interop/qemu-ga.rst b/docs/interop/qemu-ga.rst
index 72fb75a6f5..e42b370319 100644
--- a/docs/interop/qemu-ga.rst
+++ b/docs/interop/qemu-ga.rst
@@ -33,6 +33,11 @@ Options
 
 .. program:: qemu-ga
 
+.. option:: -c, --config=PATH
+
+  Configuration file path (the default is |CONFDIR|\ ``/qemu-ga.conf``,
+  unless overriden by the QGA_CONF environment variable)
+
 .. option:: -m, --method=METHOD
 
   Transport method: one of ``unix-listen``, ``virtio-serial``, or
diff --git a/qga/main.c b/qga/main.c
index 6ff022a85d..6ae911eb15 100644
--- a/qga/main.c
+++ b/qga/main.c
@@ -248,12 +248,16 @@ static void usage(const char *cmd)
 #ifdef CONFIG_FSFREEZE
     g_autofree char *fsfreeze_hook = get_relocated_path(QGA_FSFREEZE_HOOK_DEFAULT);
 #endif
+    g_autofree char *conf_path = get_relocated_path(QGA_CONF_DEFAULT);
 
     printf(
 "Usage: %s [-m <method> -p <path>] [<options>]\n"
 "QEMU Guest Agent " QEMU_FULL_VERSION "\n"
 QEMU_COPYRIGHT "\n"
 "\n"
+"  -c, --config=PATH configuration file path (default is\n"
+"                    %s/qemu-ga.conf\n"
+"                    unless overriden by the QGA_CONF environment variable)\n"
 "  -m, --method      transport method: one of unix-listen, virtio-serial,\n"
 "                    isa-serial, or vsock-listen (virtio-serial is the default)\n"
 "  -p, --path        device/socket path (the default for virtio-serial is:\n"
@@ -294,8 +298,8 @@ QEMU_COPYRIGHT "\n"
 "                    plug/unplug, etc.)\n"
 "  -h, --help        display this help and exit\n"
 "\n"
-QEMU_HELP_BOTTOM "\n"
-    , cmd, QGA_VIRTIO_PATH_DEFAULT, QGA_SERIAL_PATH_DEFAULT,
+QEMU_HELP_BOTTOM "\n",
+    cmd, conf_path, QGA_VIRTIO_PATH_DEFAULT, QGA_SERIAL_PATH_DEFAULT,
     dfl_pathnames.pidfile,
 #ifdef CONFIG_FSFREEZE
     fsfreeze_hook,
@@ -1018,15 +1022,14 @@ static GList *split_list(const gchar *str, const gchar *delim)
     return list;
 }
 
-static void config_load(GAConfig *config)
+static void config_load(GAConfig *config, const char *confpath, bool required)
 {
     GError *gerr = NULL;
     GKeyFile *keyfile;
-    g_autofree char *conf = g_strdup(g_getenv("QGA_CONF")) ?: get_relocated_path(QGA_CONF_DEFAULT);
 
     /* read system config */
     keyfile = g_key_file_new();
-    if (!g_key_file_load_from_file(keyfile, conf, 0, &gerr)) {
+    if (!g_key_file_load_from_file(keyfile, confpath, 0, &gerr)) {
         goto end;
     }
     if (g_key_file_has_key(keyfile, "general", "daemon", NULL)) {
@@ -1092,10 +1095,10 @@ static void config_load(GAConfig *config)
 
 end:
     g_key_file_free(keyfile);
-    if (gerr &&
-        !(gerr->domain == G_FILE_ERROR && gerr->code == G_FILE_ERROR_NOENT)) {
+    if (gerr && (required ||
+                 !(gerr->domain == G_FILE_ERROR && gerr->code == G_FILE_ERROR_NOENT))) {
         g_critical("error loading configuration from path: %s, %s",
-                   conf, gerr->message);
+                   confpath, gerr->message);
         exit(EXIT_FAILURE);
     }
     g_clear_error(&gerr);
@@ -1167,12 +1170,13 @@ static void config_dump(GAConfig *config)
 
 static void config_parse(GAConfig *config, int argc, char **argv)
 {
-    const char *sopt = "hVvdm:p:l:f:F::b:a:s:t:Dr";
+    const char *sopt = "hVvdc:m:p:l:f:F::b:a:s:t:Dr";
     int opt_ind = 0, ch;
     bool block_rpcs = false, allow_rpcs = false;
     const struct option lopt[] = {
         { "help", 0, NULL, 'h' },
         { "version", 0, NULL, 'V' },
+        { "config", 1, NULL, 'c' },
         { "dump-conf", 0, NULL, 'D' },
         { "logfile", 1, NULL, 'l' },
         { "pidfile", 1, NULL, 'f' },
@@ -1192,6 +1196,26 @@ static void config_parse(GAConfig *config, int argc, char **argv)
         { "retry-path", 0, NULL, 'r' },
         { NULL, 0, NULL, 0 }
     };
+    g_autofree char *confpath = g_strdup(g_getenv("QGA_CONF")) ?:
+        get_relocated_path(QGA_CONF_DEFAULT);
+    bool confrequired = false;
+
+    while ((ch = getopt_long(argc, argv, sopt, lopt, NULL)) != -1) {
+        switch (ch) {
+        case 'c':
+            g_free(confpath);
+            confpath = g_strdup(optarg);
+            confrequired = true;
+            break;
+        default:
+            break;
+        }
+    }
+
+    config_load(config, confpath, confrequired);
+
+    /* Reset for second pass */
+    optind = 1;
 
     while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
         switch (ch) {
@@ -1582,7 +1606,6 @@ int main(int argc, char **argv)
     qga_qmp_init_marshal(&ga_commands);
 
     init_dfl_pathnames();
-    config_load(config);
     config_parse(config, argc, argv);
 
     if (config->pid_filepath == NULL) {
-- 
2.45.1