error: Track locations in configuration files

New LOC_FILE.  Use it for tracking file name and line number in
qemu_config_parse().  We now report errors like

    qemu:foo.conf:42: Did not find I2C bus for smbus-eeprom

In particular, gems like this message:

    -device: no driver specified

become almost nice now:

    qemu:foo.conf:44: -device: no driver specified

(A later commit will get rid of the bogus -device:)

qemu-config.c

@@ -425,13 +425,17 @@ void qemu_config_write(FILE *fp)
     }
 }
 
-int qemu_config_parse(FILE *fp)
+int qemu_config_parse(FILE *fp, const char *fname)
 {
     char line[1024], group[64], id[64], arg[64], value[1024];
+    Location loc;
     QemuOptsList *list = NULL;
     QemuOpts *opts = NULL;
+    int res = -1, lno = 0;
 
+    loc_push_none(&loc);
     while (fgets(line, sizeof(line), fp) != NULL) {
+        loc_set_file(fname, ++lno);
         if (line[0] == '\n') {
             /* skip empty lines */
             continue;
@@ -444,7 +448,7 @@ int qemu_config_parse(FILE *fp)
             /* group with id */
             list = find_list(group);
             if (list == NULL)
-                return -1;
+                goto out;
             opts = qemu_opts_create(list, id, 1);
             continue;
         }
@@ -452,25 +456,27 @@ int qemu_config_parse(FILE *fp)
             /* group without id */
             list = find_list(group);
             if (list == NULL)
-                return -1;
+                goto out;
             opts = qemu_opts_create(list, NULL, 0);
             continue;
         }
         if (sscanf(line, " %63s = \"%1023[^\"]\"", arg, value) == 2) {
             /* arg = value */
             if (opts == NULL) {
-                fprintf(stderr, "no group defined\n");
-                return -1;
+                error_report("no group defined");
+                goto out;
             }
             if (qemu_opt_set(opts, arg, value) != 0) {
-                fprintf(stderr, "failed to set \"%s\" for %s\n",
-                        arg, group);
-                return -1;
+                error_report("failed to set \"%s\" for %s", arg, group);
+                goto out;
             }
             continue;
         }
-        fprintf(stderr, "parse error: %s\n", line);
-        return -1;
+        error_report("parse error");
+        goto out;
     }
-    return 0;
+    res = 0;
+out:
+    loc_pop(&loc);
+    return res;
 }

qemu-config.h

@@ -16,6 +16,6 @@ int qemu_global_option(const char *str);
 void qemu_add_globals(void);
 
 void qemu_config_write(FILE *fp);
-int qemu_config_parse(FILE *fp);
+int qemu_config_parse(FILE *fp, const char *fname);
 
 #endif /* QEMU_CONFIG_H */

qemu-error.c

@@ -113,6 +113,19 @@ void loc_set_none(void)
     cur_loc->kind = LOC_NONE;
 }
 
+/*
+ * Change the current location to file FNAME, line LNO.
+ */
+void loc_set_file(const char *fname, int lno)
+{
+    assert (fname || cur_loc->kind == LOC_FILE);
+    cur_loc->kind = LOC_FILE;
+    cur_loc->num = lno;
+    if (fname) {
+        cur_loc->ptr = fname;
+    }
+}
+
 static const char *progname;
 
 /*
@@ -136,6 +149,13 @@ void error_print_loc(void)
         sep = " ";
     }
     switch (cur_loc->kind) {
+    case LOC_FILE:
+        error_printf("%s:", (const char *)cur_loc->ptr);
+        if (cur_loc->num) {
+            error_printf("%d:", cur_loc->num);
+        }
+        error_printf(" ");
+        break;
     default:
         error_printf(sep);
     }

qemu-error.h

@@ -15,7 +15,7 @@
 
 typedef struct Location {
     /* all members are private to qemu-error.c */
-    enum { LOC_NONE } kind;
+    enum { LOC_NONE, LOC_FILE } kind;
     int num;
     const void *ptr;
     struct Location *prev;
@@ -27,6 +27,7 @@ Location *loc_pop(Location *loc);
 Location *loc_save(Location *loc);
 void loc_restore(Location *loc);
 void loc_set_none(void);
+void loc_set_file(const char *fname, int lno);
 
 void error_vprintf(const char *fmt, va_list ap);
 void error_printf(const char *fmt, ...) __attribute__ ((format(printf, 1, 2)));

vl.c

@@ -4941,18 +4941,22 @@ int main(int argc, char **argv, char **envp)
     }
 
     if (defconfig) {
+        const char *fname;
         FILE *fp;
-        fp = fopen(CONFIG_QEMU_CONFDIR "/qemu.conf", "r");
+
+        fname = CONFIG_QEMU_CONFDIR "/qemu.conf";
+        fp = fopen(fname, "r");
         if (fp) {
-            if (qemu_config_parse(fp) != 0) {
+            if (qemu_config_parse(fp, fname) != 0) {
                 exit(1);
             }
             fclose(fp);
         }
 
-        fp = fopen(CONFIG_QEMU_CONFDIR "/target-" TARGET_ARCH ".conf", "r");
+        fname = CONFIG_QEMU_CONFDIR "/target-" TARGET_ARCH ".conf";
+        fp = fopen(fname, "r");
         if (fp) {
-            if (qemu_config_parse(fp) != 0) {
+            if (qemu_config_parse(fp, fname) != 0) {
                 exit(1);
             }
             fclose(fp);
@@ -5633,7 +5637,7 @@ int main(int argc, char **argv, char **envp)
                         fprintf(stderr, "open %s: %s\n", optarg, strerror(errno));
                         exit(1);
                     }
-                    if (qemu_config_parse(fp) != 0) {
+                    if (qemu_config_parse(fp, optarg) != 0) {
                         exit(1);
                     }
                     fclose(fp);