On Fri, Jun 06, 2025 at 08:11:26PM +0000, [email protected] wrote:
> From: Denis Mukhin <[email protected]>
>
> 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 <[email protected]>
> ---
> 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);
It might be helpful to abstract this into a separate helper, as it's
used by both functions:
static void fill_console_prefix(char *prefix, unsigned int len,
const struct domain *d)
{
struct domain *consd = console_get_domain();
if ( consd ? consd != d : !is_hardware_domain(d)) )
snprintf(prefix, len, "(d%d) ", d->domain_id);
console_put_domain(consd);
}
Note the above code should also handle the current discussion of not
printing the (d0) prefix for the hardware domain when the console
target is Xen. I think this keeps the previous behavior when console
input is switched to Xen, while still providing unified (dX) prefixes
otherwise.
Thanks, Roger.
