qemu-option: restrict qemu_opts_set to merge-lists QemuOpts

qemu_opts_set is used to create default network backends and to
parse sugar options -kernel, -initrd, -append, -bios and -dtb.
These are very different uses:

I would *expect* a function named qemu_opts_set to set an option in a
merge-lists QemuOptsList, such as -kernel, and possibly to set an option
in a non-merge-lists QemuOptsList with non-NULL id, similar to -set.

However, it wouldn't *work* to use qemu_opts_set for the latter
because qemu_opts_set uses fail_if_exists==1. So, for non-merge-lists
QemuOptsList and non-NULL id, the semantics of qemu_opts_set (fail if the
(QemuOptsList, id) pair already exists) are debatable.

On the other hand, I would not expect qemu_opts_set to create a
non-merge-lists QemuOpts with a single option; which it does, though.
For this case of non-merge-lists QemuOptsList and NULL id, qemu_opts_set
hardly adds value over qemu_opts_parse.  It does skip some parsing and
unescaping, but that's not needed when creating default network
backends.

So qemu_opts_set has warty behavior for non-merge-lists QemuOptsList
if id is non-NULL, and it's mostly pointless if id is NULL.  My
solution to keeping the API as simple as possible is to limit
qemu_opts_set to merge-lists QemuOptsList.  For them, it's useful (we
don't want comma-unescaping for -kernel) *and* has sane semantics.
Network backend creation is switched to qemu_opts_parse.

qemu_opts_set is now only used on merge-lists QemuOptsList... except
in the testcase, which is changed to use a merge-list QemuOptsList.

With this change we can also remove the id parameter.  With the
parameter always NULL, we know that qemu_opts_create cannot fail
and can pass &error_abort to it.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 3 insertions, 6 deletions

diff --git a/util/qemu-option.c b/util/qemu-option.c
index acefbc2..2579215 100644
--- a/util/qemu-option.c
+++ b/util/qemu-option.c
@@ -670,15 +670,12 @@ void qemu_opts_loc_restore(QemuOpts *opts)
     loc_restore(&opts->loc);
 }
 
-bool qemu_opts_set(QemuOptsList *list, const char *id,
-                   const char *name, const char *value, Error **errp)
+bool qemu_opts_set(QemuOptsList *list, const char *name, const char *value, Error **errp)
 {
     QemuOpts *opts;
 
-    opts = qemu_opts_create(list, id, 1, errp);
-    if (!opts) {
-        return false;
-    }
+    assert(list->merge_lists);
+    opts = qemu_opts_create(list, NULL, 0, &error_abort);
     return qemu_opt_set(opts, name, value, errp);
 }