[14/16] hw/char/xen_console: Fix missing ERRP_GUARD() for error_prepend()

Commit Message

Zhao Liu Feb. 28, 2024, 4:37 p.m. UTC

From: Zhao Liu <[e-mail]>

As the comment in qapi/error, passing @errp to error_prepend() requires
ERRP_GUARD():

* = Why, when and how to use ERRP_GUARD() =
*
* Without ERRP_GUARD(), use of the @errp parameter is restricted:
...
* - It should not be passed to error_prepend(), error_vprepend() or
*   error_append_hint(), because that doesn't work with &error_fatal.
* ERRP_GUARD() lifts these restrictions.
*
* To use ERRP_GUARD(), add it right at the beginning of the function.
* @errp can then be used without worrying about the argument being
* NULL or &error_fatal.

ERRP_GUARD() could avoid the case when @errp is the pointer of
error_fatal, the user can't see this additional information, because
exit() happens in error_setg earlier than information is added [1].

The xen_console_connect() passes @errp to error_prepend() without
ERRP_GUARD().

There're 2 places will call xen_console_connect():
 - xen_console_realize(): the @errp is from DeviceClass.realize()'s
			  parameter.
 - xen_console_frontend_changed(): the @errp points its caller's
                                   @local_err.

To avoid the issue like [1] said, add missing ERRP_GUARD() at the
beginning of xen_console_connect().

[1]: Issue description in the commit message of commit ae7c80a7bd73
     ("error: New macro ERRP_GUARD()").

Cc: Stefano Stabellini <[e-mail]>
Cc: Anthony Perard <[e-mail]>
Cc: Paul Durrant <[e-mail]>
Cc: "Marc-André Lureau" <[e-mail]>
Cc: Paolo Bonzini <[e-mail]>
Signed-off-by: Zhao Liu <[e-mail]>
---
 hw/char/xen_console.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Anthony PERARD March 8, 2024, 3:31 p.m. UTC | #1

On Thu, Feb 29, 2024 at 12:37:21AM +0800, Zhao Liu wrote:
> From: Zhao Liu <[e-mail]>
> 
> As the comment in qapi/error, passing @errp to error_prepend() requires
> ERRP_GUARD():
> 
> * = Why, when and how to use ERRP_GUARD() =
> *
> * Without ERRP_GUARD(), use of the @errp parameter is restricted:
> ...
> * - It should not be passed to error_prepend(), error_vprepend() or
> *   error_append_hint(), because that doesn't work with &error_fatal.
> * ERRP_GUARD() lifts these restrictions.
> *
> * To use ERRP_GUARD(), add it right at the beginning of the function.
> * @errp can then be used without worrying about the argument being
> * NULL or &error_fatal.
> 
> ERRP_GUARD() could avoid the case when @errp is the pointer of
> error_fatal, the user can't see this additional information, because
> exit() happens in error_setg earlier than information is added [1].
> 
> The xen_console_connect() passes @errp to error_prepend() without
> ERRP_GUARD().
> 
> There're 2 places will call xen_console_connect():
>  - xen_console_realize(): the @errp is from DeviceClass.realize()'s
> 			  parameter.
>  - xen_console_frontend_changed(): the @errp points its caller's
>                                    @local_err.
> 
> To avoid the issue like [1] said, add missing ERRP_GUARD() at the
> beginning of xen_console_connect().
> 
> [1]: Issue description in the commit message of commit ae7c80a7bd73
>      ("error: New macro ERRP_GUARD()").
> 
> Cc: Stefano Stabellini <[e-mail]>
> Cc: Anthony Perard <[e-mail]>
> Cc: Paul Durrant <[e-mail]>
> Cc: "Marc-André Lureau" <[e-mail]>
> Cc: Paolo Bonzini <[e-mail]>
> Signed-off-by: Zhao Liu <[e-mail]>

Acked-by: Anthony PERARD <[e-mail]>

Thanks,

Patch

diff --git a/hw/char/xen_console.c b/hw/char/xen_console.c
index 5cbee2f184d8..683c92aca1ce 100644
--- a/hw/char/xen_console.c
+++ b/hw/char/xen_console.c
@@ -206,6 +206,7 @@  static bool con_event(void *_xendev)
 
 static bool xen_console_connect(XenDevice *xendev, Error **errp)
 {
+    ERRP_GUARD();
     XenConsole *con = XEN_CONSOLE_DEVICE(xendev);
     unsigned int port, limit;