[v2,23/35] xen/console: introduce console_write()

Commit Message

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

From: Denis Mukhin <[e-mail]>

PV Linux kernel uses HYPERVISOR_console_io hypercall for early console which
ends up being handled by Xen's console driver's guest_console_write().

guest_console_write() duplicates the code from __putstr(), elimitate code
duplication.

Signed-off-by: Denis Mukhin <[e-mail]>
---
 xen/drivers/char/console.c | 97 +++++++++++++++++++++++++---------------------
 1 file changed, 53 insertions(+), 44 deletions(-)

Patch

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index ce3639a4cdcda00ea63e3bf119bc3b242cbfdf6a..115967d179998cba4a81578caba09db4e4aca7f7 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -63,6 +63,8 @@  static const char __initconst warning_sync_console[] =
     "However it can introduce SIGNIFICANT latencies and affect\n"
     "timekeeping. It is NOT recommended for production use!\n";
 
+/* Flag: use conring for early console; switches to opt_console_to_ring */
+static bool __read_mostly use_conring = true;
 /* console_to_ring: send guest (incl. dom 0) console data to console ring. */
 static bool __read_mostly opt_console_to_ring;
 boolean_param("console_to_ring", opt_console_to_ring);
@@ -661,6 +663,16 @@  static void cf_check notify_dom0_con_ring(void *unused)
 static DECLARE_SOFTIRQ_TASKLET(notify_dom0_con_ring_tasklet,
                                notify_dom0_con_ring, NULL);
 
+static bool console_locks_busted;
+
+static void conring_write(const char *str, size_t len)
+{
+    conring_puts(str, len);
+
+    if ( !console_locks_busted )
+        tasklet_schedule(&notify_dom0_con_ring_tasklet);
+}
+
 #ifdef CONFIG_X86
 static inline void xen_console_write_debug_port(const char *buf, size_t len)
 {
@@ -669,8 +681,44 @@  static inline void xen_console_write_debug_port(const char *buf, size_t len)
                    : "=&S" (tmp), "=&c" (tmp)
                    : "0" (buf), "1" (len), "d" (XEN_HVM_DEBUGCONS_IOPORT) );
 }
+
+static void xen_console_write(const char *str, size_t len)
+{
+    if ( xen_guest )
+        xen_hypercall_console_write(str, len);
+    else
+        xen_console_write_debug_port(str, len);
+}
+#else
+static inline void xen_console_write(const char *str, size_t len)
+{
+}
 #endif
 
+/*
+ * Write characters to console.
+ *
+ * That will handle all possible scenarios working w/ console
+ * - serial console;
+ * - video output;
+ * - __HYPERVISOR_console_io hypercall (x86 only);
+ * - debug I/O port (x86 only);
+ * - forward to Xen event channel.
+ */
+static void console_write(const char *str, size_t len)
+{
+    ASSERT(rspin_is_locked(&console_lock));
+
+    console_serial_puts(str, len);
+    video_puts(str, len);
+
+    if ( opt_console_xen )
+        xen_console_write(str, len);
+
+    if ( use_conring )
+        conring_write(str, len);
+}
+
 static long guest_console_write(XEN_GUEST_HANDLE_PARAM(char) buffer,
                                 unsigned int count)
 {
@@ -691,28 +739,8 @@  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 */
             nrspin_lock_irq(&console_lock);
-
-            console_serial_puts(kbuf, kcount);
-            video_puts(kbuf, kcount);
-
-#ifdef CONFIG_X86
-            if ( opt_console_xen )
-            {
-                if ( xen_guest )
-                    xen_hypercall_console_write(kbuf, kcount);
-                else
-                    xen_console_write_debug_port(kbuf, kcount);
-            }
-#endif
-
-            if ( opt_console_to_ring )
-            {
-                conring_puts(kbuf, kcount);
-                tasklet_schedule(&notify_dom0_con_ring_tasklet);
-            }
-
+            console_write(kbuf, kcount);
             nrspin_unlock_irq(&console_lock);
         }
         else
@@ -813,31 +841,9 @@  long do_console_io(
  * *****************************************************
  */
 
-static bool console_locks_busted;
-
 static void __putstr(const char *str)
 {
-    size_t len = strlen(str);
-
-    ASSERT(rspin_is_locked(&console_lock));
-
-    console_serial_puts(str, len);
-    video_puts(str, len);
-
-#ifdef CONFIG_X86
-    if ( opt_console_xen )
-    {
-        if ( xen_guest )
-            xen_hypercall_console_write(str, len);
-        else
-            xen_console_write_debug_port(str, len);
-    }
-#endif
-
-    conring_puts(str, len);
-
-    if ( !console_locks_busted )
-        tasklet_schedule(&notify_dom0_con_ring_tasklet);
+    console_write(str, strlen(str));
 }
 
 static int printk_prefix_check(char *p, char **pp)
@@ -1171,6 +1177,9 @@  void __init console_endboot(void)
 
     video_endboot();
 
+    use_conring = opt_console_to_ring;
+    smp_wmb();
+
     register_keyhandler('w', dump_console_ring_key,
                         "synchronously dump console ring buffer (dmesg)", 0);
     register_irq_keyhandler('+', &do_inc_thresh,