[Qemu-devel] [RHEL6 qemu-kvm PATCH 04/11] Support -readconfig "?" to debug config file loading

[Eduardo Habkost <ehabkost@redhat.com>]

From: john cooper <john.cooper@redhat.com>

Failure by qemu to open a default config file isn't cause to
error exit -- it just quietly continues on.   After puzzling
issues with otherwise opaque config file locations and
startup handling numerous times, some help from qemu seemed
justified.

In the case of a "?" pseudo filename arg to -readconfig,
verbose open of all config files will be enabled.  Normal
handling of config files is otherwise unaffected by this
option.

Note: other CLI flag schemes have been discussed at length
to accommodate this option.  However given the constraints
of the existing user interface, a solution which minimally
impacts the user is ultimately required.

[ehabkost: edited commit message to have better Subject line]

Signed-off-by: john cooper <john.cooper@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu-config.c |   30 +++++++++++++++++++-----------
 qemu-config.h |    2 +-
 vl.c          |   20 +++++++++++++-------
 3 files changed, 33 insertions(+), 19 deletions(-)

diff --git a/qemu-config.c b/qemu-config.c
index 5d7ffa2..b39b8fe 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -666,21 +666,29 @@ out:
     return res;
 }
 
-int qemu_read_config_file(const char *filename)
+/* attempt to open and parse config file, report problems if vflag
+ */
+int qemu_read_config_file(const char *filename, int vflag)
 {
     FILE *f = fopen(filename, "r");
-    int ret;
+    int rv = 0;
+    const char *err;
 
     if (f == NULL) {
-        return -errno;
+        rv = -errno;
+        err = "open";
+    } else if (qemu_config_parse(f, vm_config_groups, filename) != 0) {
+        rv = -EINVAL;
+        err = "parse";
+    } else if (vflag) {
+        fprintf(stderr, "parsed config file %s\n", filename);
     }
-
-    ret = qemu_config_parse(f, vm_config_groups, filename);
-    fclose(f);
-
-    if (ret == 0) {
-        return 0;
-    } else {
-        return -EINVAL;
+    if (f) {
+        fclose(f);
+    }
+    if (rv && vflag) {
+        fprintf(stderr, "can't %s config file %s: %s\n",
+                err, filename, strerror(-rv));
     }
+    return rv;
 }
diff --git a/qemu-config.h b/qemu-config.h
index 20d707f..b90a7cc 100644
--- a/qemu-config.h
+++ b/qemu-config.h
@@ -14,6 +14,6 @@ void qemu_add_globals(void);
 void qemu_config_write(FILE *fp);
 int qemu_config_parse(FILE *fp, QemuOptsList **lists, const char *fname);
 
-int qemu_read_config_file(const char *filename);
+int qemu_read_config_file(const char *filename, int vflag);
 
 #endif /* QEMU_CONFIG_H */
diff --git a/vl.c b/vl.c
index b362871..65b0791 100644
--- a/vl.c
+++ b/vl.c
@@ -2059,6 +2059,7 @@ int main(int argc, char **argv, char **envp)
     int show_vnc_port = 0;
 #endif
     int defconfig = 1;
+    int defconfig_verbose = 0;
     const char *trace_file = NULL;
 
     atexit(qemu_run_exit_notifiers);
@@ -2108,6 +2109,12 @@ int main(int argc, char **argv, char **envp)
             case QEMU_OPTION_nodefconfig:
                 defconfig=0;
                 break;
+            case QEMU_OPTION_readconfig:
+                /* pseudo filename "?" enables verbose config file handling */
+                if (!strcmp(optarg, "?")) {
+                    defconfig_verbose = 1;
+                }
+                break;
             }
         }
     }
@@ -2115,12 +2122,13 @@ int main(int argc, char **argv, char **envp)
     if (defconfig) {
         int ret;
 
-        ret = qemu_read_config_file(CONFIG_QEMU_CONFDIR "/qemu.conf");
+        ret = qemu_read_config_file(CONFIG_QEMU_CONFDIR "/qemu.conf",
+                                    defconfig_verbose);
         if (ret < 0 && ret != -ENOENT) {
             exit(1);
         }
 
-        ret = qemu_read_config_file(arch_config_name);
+        ret = qemu_read_config_file(arch_config_name, defconfig_verbose);
         if (ret < 0 && ret != -ENOENT) {
             exit(1);
         }
@@ -2857,11 +2865,9 @@ int main(int argc, char **argv, char **envp)
 #endif
             case QEMU_OPTION_readconfig:
                 {
-                    int ret = qemu_read_config_file(optarg);
-                    if (ret < 0) {
-                        fprintf(stderr, "read config %s: %s\n", optarg,
-                            strerror(-ret));
-                        exit(1);
+                    if (strcmp(optarg, "?") &&
+                        qemu_read_config_file(optarg, defconfig_verbose) < 0) {
+                            exit(1);
                     }
                     break;
                 }
-- 
1.7.3.2