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Jason Andryuk
ddc2dd1264
With hyperlaunch, a domU can start before its console ring is connected
by xenconsoled. With nothing emptying the ring, it can quickly fill
during boot. In domU_write_console(), __write_console() returns 0 when
the ring is full. This loops spins until xenconsoled starts emptying
the ring:
while (len) {
ssize_t sent = __write_console(cons, data, len);
if (sent < 0)
return sent;
data += sent;
len -= sent;
if (unlikely(len))
HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
}
The goal of this patch is to add a way for the frontend to know when a
console is connected. This patch adds a new flag to the end of the
console ring structure. It is used for the backend to indicate that it
has connected and started servicing the page.
The two values are
XENCONSOLE_DISCONNECTED 1
XENCONSOLE_CONNECTED 0
XENCONSOLE_DISCONNECTED indicates to the guest that ring is
disconnected, so it will not be serviced. The guest can avoid writing
into it in that case. A domU can use console hypercalls and only
transition to the ring when it is connected and won't fill and block.
Once the backend (xenconsoled) maps and starts servicing the
console, the flag will be set to XENCONSOLE_CONNECTED (0) to indicate
the backend state to the frontend.
The connected value as 0 will be match the default of a zero-ed console
page. Hyperlaunch can set the flag to XENCONSOLE_DISCONNECTED and let
xenconsoled set to XENCONSOLE_CONNECTED.
Old domU hvc_xen drivers won't check the flag.
New domU hvc_xen running on a new xen/xenconsoled will work properly.
New domU hvc_xen on old xen/xenconsoled should only see a 0 for the flag
and behave as if connected.
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Release-Acked-By: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>