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

Commit Message

Denis Mukhin via B4 Relay Dec. 6, 2024, 4:41 a.m. UTC

From: Denis Mukhin <[e-mail]>

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.

Signed-off-by: Denis Mukhin <[e-mail]>
---
 xen/drivers/char/console.c | 5 +++++
 xen/include/xen/console.h  | 1 +
 2 files changed, 6 insertions(+)

Comments

Jason Andryuk Dec. 10, 2024, 10:11 p.m. UTC | #1

On 2024-12-05 23:41, Denis Mukhin via B4 Relay wrote:
> From: Denis Mukhin <[e-mail]>
> 
> 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.
> 
> Signed-off-by: Denis Mukhin <[e-mail]>

Reviewed-by: Jason Andryuk <[e-mail]>

I expected this to be used immediately by patch 21, but it is not.  You 
might want to re-order it directly before its first use is introduced. 
I haven't gotten far enough to know when that is.

Regards,
Jason

Jan Beulich Dec. 11, 2024, 7:28 a.m. UTC | #2

On 06.12.2024 05:41, Denis Mukhin via B4 Relay wrote:
> From: Denis Mukhin <[e-mail]>
> 
> 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.

Such messages ought to be processed through guest_printk(), which wants a
domain pointer, not a domid_t anyway. Plus isn't that going to be
current->domain anyway at the callsite, eliminating the need for such a
helper altogether?

Jan

Jan Beulich Dec. 11, 2024, 7:33 a.m. UTC | #3

On 10.12.2024 23:11, Jason Andryuk wrote:
> On 2024-12-05 23:41, Denis Mukhin via B4 Relay wrote:
>> From: Denis Mukhin <[e-mail]>
>>
>> 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.
>>
>> Signed-off-by: Denis Mukhin <[e-mail]>
> 
> Reviewed-by: Jason Andryuk <[e-mail]>
> 
> I expected this to be used immediately by patch 21, but it is not.  You 
> might want to re-order it directly before its first use is introduced. 
> I haven't gotten far enough to know when that is.

Plus, no matter how far in the future it is, there'll be a window where the
Misra rule of not having unreachable code in the project is violated. New
functions now really need introducing when their first caller appears.

Jan

Patch

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);
 
 /*
  * Steal output from the console. Returns +ve identifier, else -ve error.