Re: [PATCH v2 20/35] xen/console: introduce console_owner_domid()

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Dec 05, 2024 at 08:41:50PM -0800, Denis Mukhin via B4 Relay wrote:
> From: Denis Mukhin <dmukhin@xxxxxxxx>
> 
> console_owner_domid() is introduced to obtain the "console owner" domain ID.
> 
> The call is used in NS8250 emulator to identify the case when physical xen
> console focus is owned by the domain w/ NS8250 emulator, in which case,
> messages from guest OS are formatted w/o '(XEN)' prefix.

Nit: it would be better to not use abbreviations such as w/ or w/o in
commit messages.

> 
> Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
> ---
>  xen/drivers/char/console.c | 5 +++++
>  xen/include/xen/console.h  | 1 +
>  2 files changed, 6 insertions(+)
> 
> diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
> index 
> 52cf64dbf6fd18d599cb88835d03501a23b3e3c4..a8ab5c2bcb98e4cadf9ad2c9ad28d297977d0557
>  100644
> --- a/xen/drivers/char/console.c
> +++ b/xen/drivers/char/console.c
> @@ -498,6 +498,11 @@ struct domain *rcu_lock_domain_console_owner(void)
>      return rcu_lock_domain_console_by_id(console_owner);
>  }
>  
> +domid_t console_owner_domid(void)
> +{
> +    return console_owner;
> +}
> +
>  static bool console_owner_possible(domid_t domid)
>  {
>      struct domain *d;
> diff --git a/xen/include/xen/console.h b/xen/include/xen/console.h
> index 
> 57c482cfbf2da15b011e64841ea086e779f4588d..83be5794aff6630beaad46f910fcc0fc6d833808
>  100644
> --- a/xen/include/xen/console.h
> +++ b/xen/include/xen/console.h
> @@ -33,6 +33,7 @@ void console_end_log_everything(void);
>  
>  struct domain *rcu_lock_domain_console_owner(void);
>  int console_set_owner(domid_t);
> +domid_t console_owner_domid(void);

I would expect that either the caller already has a domain locked, or
uses rcu_lock_domain_console_owner() to obtain the domain and then get
the domid?  (d->domain_id?)

It's hard to tell why you need such way to get the console input
target domid in such a way without seeing a caller to the function.

Thanks, Roger.