[PATCH 2/4] backends: Improve error messages when property can no longer be set

[Markus Armbruster <armbru@redhat.com>]

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>

# This is the commit message #2:

# fixup! backends: Improve error messages when property can no longer be set
---
 backends/cryptodev-vhost-user.c | 2 +-
 backends/rng-egd.c              | 2 +-
 backends/rng-random.c           | 2 +-
 backends/vhost-user.c           | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/backends/cryptodev-vhost-user.c b/backends/cryptodev-vhost-user.c
index 5443a59153..f9c5867e38 100644
--- a/backends/cryptodev-vhost-user.c
+++ b/backends/cryptodev-vhost-user.c
@@ -339,7 +339,7 @@ static void cryptodev_vhost_user_set_chardev(Object *obj,
                       CRYPTODEV_BACKEND_VHOST_USER(obj);
 
     if (s->opened) {
-        error_setg(errp, QERR_PERMISSION_DENIED);
+        error_setg(errp, "Property 'chardev' can no longer be set");
     } else {
         g_free(s->chr_name);
         s->chr_name = g_strdup(value);
diff --git a/backends/rng-egd.c b/backends/rng-egd.c
index 4de142b9dc..684c3cf3d6 100644
--- a/backends/rng-egd.c
+++ b/backends/rng-egd.c
@@ -116,7 +116,7 @@ static void rng_egd_set_chardev(Object *obj, const char *value, Error **errp)
     RngEgd *s = RNG_EGD(b);
 
     if (b->opened) {
-        error_setg(errp, QERR_PERMISSION_DENIED);
+        error_setg(errp, "Property 'chardev' can no longer be set");
     } else {
         g_free(s->chr_name);
         s->chr_name = g_strdup(value);
diff --git a/backends/rng-random.c b/backends/rng-random.c
index 7add272edd..80eb5be138 100644
--- a/backends/rng-random.c
+++ b/backends/rng-random.c
@@ -96,7 +96,7 @@ static void rng_random_set_filename(Object *obj, const char *filename,
     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;
     }
 
diff --git a/backends/vhost-user.c b/backends/vhost-user.c
index 10b39992d2..5dedb2d987 100644
--- a/backends/vhost-user.c
+++ b/backends/vhost-user.c
@@ -141,7 +141,7 @@ static void set_chardev(Object *obj, const char *value, Error **errp)
     Chardev *chr;
 
     if (b->completed) {
-        error_setg(errp, QERR_PERMISSION_DENIED);
+        error_setg(errp, "Property 'chardev' can no longer be set");
         return;
     }
 
-- 
2.37.2