qemu-img: Suppress unhelpful extra errors in convert, amend

img_convert() and img_amend() use qemu_opts_do_parse(), which reports
errors with qerror_report_err().  Its error messages aren't helpful
here, the caller reports one that actually makes sense.  Reproducer:

    $ qemu-img convert -o backing_format=raw in.img out.img
    qemu-img: Invalid parameter 'backing_format'
    qemu-img: Invalid options for file format 'raw'

To fix, propagate errors through qemu_opts_do_parse().  This lifts the
error reporting into callers.  Drop it from img_convert() and
img_amend(), keep it in qemu_chr_parse_compat(), bdrv_img_create().

Since I'm touching qemu_opts_do_parse() anyway, write a function
comment for it.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

block.c

@@ -5653,7 +5653,10 @@ void bdrv_img_create(const char *filename, const char *fmt,
 
     /* Parse -o options */
     if (options) {
-        if (qemu_opts_do_parse(opts, options, NULL) != 0) {
+        qemu_opts_do_parse(opts, options, NULL, &local_err);
+        if (local_err) {
+            error_report_err(local_err);
+            local_err = NULL;
             error_setg(errp, "Invalid options for file format '%s'", fmt);
             goto out;
         }

include/qemu/option.h

@@ -115,7 +115,8 @@ const char *qemu_opts_id(QemuOpts *opts);
 void qemu_opts_set_id(QemuOpts *opts, char *id);
 void qemu_opts_del(QemuOpts *opts);
 void qemu_opts_validate(QemuOpts *opts, const QemuOptDesc *desc, Error **errp);
-int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname);
+void qemu_opts_do_parse(QemuOpts *opts, const char *params,
+                        const char *firstname, Error **errp);
 QemuOpts *qemu_opts_parse(QemuOptsList *list, const char *params, int permit_abbrev);
 void qemu_opts_set_defaults(QemuOptsList *list, const char *params,
                             int permit_abbrev);

qemu-char.c

@@ -3379,9 +3379,12 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
         qemu_opt_set(opts, "host", host, &error_abort);
         qemu_opt_set(opts, "port", port, &error_abort);
         if (p[pos] == ',') {
-            if (qemu_opts_do_parse(opts, p+pos+1, NULL) != 0)
+            qemu_opts_do_parse(opts, p+pos+1, NULL, &local_err);
+            if (local_err) {
+                error_report_err(local_err);
                 goto fail;
             }
+        }
         if (strstart(filename, "telnet:", &p))
             qemu_opt_set(opts, "telnet", "on", &error_abort);
         return opts;
@@ -3411,8 +3414,11 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
     }
     if (strstart(filename, "unix:", &p)) {
         qemu_opt_set(opts, "backend", "socket", &error_abort);
-        if (qemu_opts_do_parse(opts, p, "path") != 0)
+        qemu_opts_do_parse(opts, p, "path", &local_err);
+        if (local_err) {
+            error_report_err(local_err);
             goto fail;
+        }
         return opts;
     }
     if (strstart(filename, "/dev/parport", NULL) ||

qemu-img.c

@@ -1550,11 +1550,15 @@ static int img_convert(int argc, char **argv)
         create_opts = qemu_opts_append(create_opts, proto_drv->create_opts);
 
         opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
-        if (options && qemu_opts_do_parse(opts, options, NULL)) {
+        if (options) {
+            qemu_opts_do_parse(opts, options, NULL, &local_err);
+            if (local_err) {
                 error_report("Invalid options for file format '%s'", out_fmt);
+                error_free(local_err);
                 ret = -1;
                 goto out;
             }
+        }
 
         qemu_opt_set_number(opts, BLOCK_OPT_SIZE, total_sectors * 512,
                             &error_abort);
@@ -2887,6 +2891,7 @@ static void amend_status_cb(BlockDriverState *bs,
 
 static int img_amend(int argc, char **argv)
 {
+    Error *err = NULL;
     int c, ret = 0;
     char *options = NULL;
     QemuOptsList *create_opts = NULL;
@@ -2992,11 +2997,15 @@ static int img_amend(int argc, char **argv)
 
     create_opts = qemu_opts_append(create_opts, bs->drv->create_opts);
     opts = qemu_opts_create(create_opts, NULL, 0, &error_abort);
-    if (options && qemu_opts_do_parse(opts, options, NULL)) {
+    if (options) {
+        qemu_opts_do_parse(opts, options, NULL, &err);
+        if (err) {
             error_report("Invalid options for file format '%s'", fmt);
+            error_free(err);
             ret = -1;
             goto out;
         }
+    }
 
     /* In case the driver does not call amend_status_cb() */
     qemu_progress_print(0.f, 0);

util/qemu-option.c

@@ -799,17 +799,16 @@ static void opts_do_parse(QemuOpts *opts, const char *params,
     }
 }
 
-int qemu_opts_do_parse(QemuOpts *opts, const char *params, const char *firstname)
+/**
+ * Store options parsed from @params into @opts.
+ * If @firstname is non-null, the first key=value in @params may omit
+ * key=, and is treated as if key was @firstname.
+ * On error, store an error object through @errp if non-null.
+ */
+void qemu_opts_do_parse(QemuOpts *opts, const char *params,
+                       const char *firstname, Error **errp)
 {
-    Error *err = NULL;
-
-    opts_do_parse(opts, params, firstname, false, &err);
-    if (err) {
-        qerror_report_err(err);
-        error_free(err);
-        return -1;
-    }
-    return 0;
+    opts_do_parse(opts, params, firstname, false, errp);
 }
 
 static QemuOpts *opts_parse(QemuOptsList *list, const char *params,