char: Slightly better error reporting when chardev is in use

[PATCH] char: Slightly better error reporting when chardev is in use

Posted by Markus Armbruster 8 months, 3 weeks ago

Both

    $ qemu-system-x86_64 -chardev null,id=chr0,mux=on -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0

and

    $ qemu-system-x86_64 -chardev null,id=chr0 -mon chardev=chr0 -mon chardev=chr0
fail with

    qemu-system-x86_64: -mon chardev=chr0: Device 'chr0' is in use

Improve to

    qemu-system-x86_64: -mon chardev=chr0: too many uses of multiplexed chardev 'chr0' (maximum is 4)

and

    qemu-system-x86_64: -mon chardev=chr0: chardev 'chr0' is already in use

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 chardev/char-fe.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/chardev/char-fe.c b/chardev/char-fe.c
index 20222a4cad..66cee8475a 100644
--- a/chardev/char-fe.c
+++ b/chardev/char-fe.c
@@ -199,13 +199,18 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
             MuxChardev *d = MUX_CHARDEV(s);
 
             if (d->mux_cnt >= MAX_MUX) {
-                goto unavailable;
+                error_setg(errp,
+                           "too many uses of multiplexed chardev '%s'"
+                           " (maximum is " stringify(MAX_MUX) ")",
+                           s->label);
+                return false;
             }
 
             d->backends[d->mux_cnt] = b;
             tag = d->mux_cnt++;
         } else if (s->be) {
-            goto unavailable;
+            error_setg(errp, "chardev '%s' is already in use", s->label);
+            return false;
         } else {
             s->be = b;
         }
@@ -215,10 +220,6 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
     b->tag = tag;
     b->chr = s;
     return true;
-
-unavailable:
-    error_setg(errp, QERR_DEVICE_IN_USE, s->label);
-    return false;
 }
 
 void qemu_chr_fe_deinit(CharBackend *b, bool del)
-- 
2.44.0

Re: [PATCH] char: Slightly better error reporting when chardev is in use

Posted by Marc-André Lureau 8 months, 3 weeks ago

Hi

On Wed, Mar 6, 2024 at 12:15 PM Markus Armbruster <armbru@redhat.com> wrote:
>
> Both
>
>     $ qemu-system-x86_64 -chardev null,id=chr0,mux=on -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0
>
> and
>
>     $ qemu-system-x86_64 -chardev null,id=chr0 -mon chardev=chr0 -mon chardev=chr0
> fail with
>
>     qemu-system-x86_64: -mon chardev=chr0: Device 'chr0' is in use
>
> Improve to
>
>     qemu-system-x86_64: -mon chardev=chr0: too many uses of multiplexed chardev 'chr0' (maximum is 4)
>
> and
>
>     qemu-system-x86_64: -mon chardev=chr0: chardev 'chr0' is already in use
>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

lgtm
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  chardev/char-fe.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/chardev/char-fe.c b/chardev/char-fe.c
> index 20222a4cad..66cee8475a 100644
> --- a/chardev/char-fe.c
> +++ b/chardev/char-fe.c
> @@ -199,13 +199,18 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
>              MuxChardev *d = MUX_CHARDEV(s);
>
>              if (d->mux_cnt >= MAX_MUX) {
> -                goto unavailable;
> +                error_setg(errp,
> +                           "too many uses of multiplexed chardev '%s'"
> +                           " (maximum is " stringify(MAX_MUX) ")",
> +                           s->label);
> +                return false;
>              }
>
>              d->backends[d->mux_cnt] = b;
>              tag = d->mux_cnt++;
>          } else if (s->be) {
> -            goto unavailable;
> +            error_setg(errp, "chardev '%s' is already in use", s->label);
> +            return false;
>          } else {
>              s->be = b;
>          }
> @@ -215,10 +220,6 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
>      b->tag = tag;
>      b->chr = s;
>      return true;
> -
> -unavailable:
> -    error_setg(errp, QERR_DEVICE_IN_USE, s->label);

QERR_DEVICE_IN_USE is now left with a single user in blockdev.c. Is it worth it?


-- 
Marc-André Lureau

Re: [PATCH] char: Slightly better error reporting when chardev is in use

Posted by Markus Armbruster 8 months, 3 weeks ago

Marc-André Lureau <marcandre.lureau@gmail.com> writes:

> Hi
>
> On Wed, Mar 6, 2024 at 12:15 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Both
>>
>>     $ qemu-system-x86_64 -chardev null,id=chr0,mux=on -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0 -mon chardev=chr0
>>
>> and
>>
>>     $ qemu-system-x86_64 -chardev null,id=chr0 -mon chardev=chr0 -mon chardev=chr0
>> fail with
>>
>>     qemu-system-x86_64: -mon chardev=chr0: Device 'chr0' is in use
>>
>> Improve to
>>
>>     qemu-system-x86_64: -mon chardev=chr0: too many uses of multiplexed chardev 'chr0' (maximum is 4)
>>
>> and
>>
>>     qemu-system-x86_64: -mon chardev=chr0: chardev 'chr0' is already in use
>>
>> Signed-off-by: Markus Armbruster <armbru@redhat.com>
>
> lgtm
> Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Thanks!

[...]

> QERR_DEVICE_IN_USE is now left with a single user in blockdev.c. Is it worth it?

Nope, that one needs to go, too.  How to reproduce it isn't obvious to
me.  I'll figure it out.