[PATCH v3 2/2] xen/console: unify printout behavior for UART emulators

[dmkhn@xxxxxxxxx]

From: Denis Mukhin <dmukhin@xxxxxxxx>

If virtual UART from domain X prints on the physical console, the behavior is
updated to (see [1]):
- console focus in domain X: do not prefix messages;
- no console focus in domain X: prefix all messages with "(dX)".

Use guest_printk() in all current in-hypervisor UART emulators. That aligns the
behavior with debug I/O port 0xe9 handler on x86 and slightly improves the
logging since guest_printk() already prints the domain ID. guest_printk() was
modified to account for console focus ownership.

Modify guest_console_write() for hardware domain case by adding domain ID to
the message when hwdom does not have console focus.

[1] 
https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2412121655360.463523@ubuntu-linux-20-04-desktop/
Signed-off-by: Denis Mukhin <dmukhin@xxxxxxxx>
---
Changes since v2:
- dropped rate-limiting change for vuart
---
 xen/arch/arm/vpl011.c      |  6 +++---
 xen/arch/arm/vuart.c       |  2 +-
 xen/drivers/char/console.c | 23 +++++++++++++++++++++--
 3 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index 480fc664fc..2b6f2a09bc 100644
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -87,7 +87,7 @@ static void vpl011_write_data_xen(struct domain *d, uint8_t 
data)
     {
         if ( intf->out_prod == 1 )
         {
-            printk("%c", data);
+            guest_printk(d, "%c", data);
             intf->out_prod = 0;
         }
         else
@@ -95,7 +95,7 @@ static void vpl011_write_data_xen(struct domain *d, uint8_t 
data)
             if ( data != '\n' )
                 intf->out[intf->out_prod++] = '\n';
             intf->out[intf->out_prod++] = '\0';
-            printk("%s", intf->out);
+            guest_printk(d, "%s", intf->out);
             intf->out_prod = 0;
         }
     }
@@ -107,7 +107,7 @@ static void vpl011_write_data_xen(struct domain *d, uint8_t 
data)
             if ( data != '\n' )
                 intf->out[intf->out_prod++] = '\n';
             intf->out[intf->out_prod++] = '\0';
-            printk("DOM%u: %s", d->domain_id, intf->out);
+            guest_printk(d, "%s", intf->out);
             intf->out_prod = 0;
         }
     }
diff --git a/xen/arch/arm/vuart.c b/xen/arch/arm/vuart.c
index bd2f425214..6641f9d775 100644
--- a/xen/arch/arm/vuart.c
+++ b/xen/arch/arm/vuart.c
@@ -89,7 +89,7 @@ static void vuart_print_char(struct vcpu *v, char c)
         if ( c != '\n' )
             uart->buf[uart->idx++] = '\n';
         uart->buf[uart->idx] = '\0';
-        printk(XENLOG_G_DEBUG "DOM%u: %s", d->domain_id, uart->buf);
+        guest_printk(d, XENLOG_G_DEBUG "%s", uart->buf);
         uart->idx = 0;
     }
     spin_unlock(&uart->lock);
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 6e77b4af82..3855962af7 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -740,7 +740,17 @@ static long 
guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer,
         if ( is_hardware_domain(cd) )
         {
             /* Use direct console output as it could be interactive */
+            char prefix[16] = "";
+            struct domain *consd;
+
+            consd = console_get_domain();
+            if ( consd != cd )
+                snprintf(prefix, sizeof(prefix), "(d%d) ", cd->domain_id);
+            console_put_domain(consd);
+
             nrspin_lock_irq(&console_lock);
+            if ( prefix[0] != '\0' )
+                console_send(prefix, strlen(prefix), flags);
             console_send(kbuf, kcount, flags);
             nrspin_unlock_irq(&console_lock);
         }
@@ -1032,12 +1042,21 @@ void printk(const char *fmt, ...)
     va_end(args);
 }
 
+/*
+ * Print message from the guest on the diagnostic console.
+ * Prefixes all messages w/ "(dX)" if domain X does not own physical console
+ * focus.
+ */
 void guest_printk(const struct domain *d, const char *fmt, ...)
 {
     va_list args;
-    char prefix[16];
+    char prefix[16] = "";
+    struct domain *consd;
 
-    snprintf(prefix, sizeof(prefix), "(d%d) ", d->domain_id);
+    consd = console_get_domain();
+    if ( consd != d )
+        snprintf(prefix, sizeof(prefix), "(d%d) ", d->domain_id);
+    console_put_domain(consd);
 
     va_start(args, fmt);
     vprintk_common(fmt, args, prefix);
-- 
2.34.1