commit ff924448849f4fca48df15ecad67dc93854392e5
author Markus Armbruster <armbru@redhat.com> Wed Oct 12 17:37:59 2022 +0200
committer Markus Armbruster <armbru@redhat.com> Thu Oct 27 07:56:56 2022 +0200
tree 73797ff424969e0b3d5a42d57dbdd40d64aaba9f
parent 3f7febc93785bf0e622072b01f846d2acbcd9c0b

backends: Improve error messages when property can no longer be set

When you try to set virtio-rng property "filename" after the backend
has been completed with user_creatable_complete(), the error message
blames "insufficient permission":

    $ qemu-system-x86_64 -S -display none -nodefaults -monitor stdio -object rng-random,id=rng0 -device virtio-rng,id=vrng0,rng=rng0
    QEMU 7.1.50 monitor - type 'help' for more information
    (qemu) qom-set /objects/rng0 filename /dev/random
    Error: Insufficient permission to perform this operation

This implies it could work with "sufficient permission".  It can't.
Change the error message to:

    Error: Property 'filename' can no longer be set

Same for cryptodev-vhost-user property "chardev", rng-egd property
"chardev", and vhost-user-backend property "chardev".

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20221012153801.2604340-3-armbru@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
[Commit message tidied up]

backends/rng-random.c

diff --git a/backends/rng-random.c b/backends/rng-random.c
index 7add272..80eb5be 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -96,7 +96,7 @@
     RngRandom *s = RNG_RANDOM(obj);
 
     if (b->opened) {
-        error_setg(errp, QERR_PERMISSION_DENIED);
+        error_setg(errp, "Property 'filename' can no longer be set");
         return;
     }