[Xen-devel] [PATCH] console: allow log level threshold adjustments from serial console

["Jan Beulich" <JBeulich@xxxxxxxx>]

... so that one doesn't always need to reboot to see more / fewer
messages.

Note that upper thresholds are sticky, i.e. while they get adjusted
upwards when the lower threshold would otherwise end up above the upper
one, they don't get adjusted when reducing the lower one.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
TBD: Should we also add a (more flexible) sysctl?

--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -168,7 +168,7 @@ static void __init parse_guest_loglvl(ch
     _parse_loglvl(s, &xenlog_guest_lower_thresh, &xenlog_guest_upper_thresh);
 }
 
-static char * __init loglvl_str(int lvl)
+static char *loglvl_str(int lvl)
 {
     switch ( lvl )
     {
@@ -181,6 +181,66 @@ static char * __init loglvl_str(int lvl)
     return "???";
 }
 
+static int *__read_mostly upper_thresh_adj = &xenlog_upper_thresh;
+static int *__read_mostly lower_thresh_adj = &xenlog_lower_thresh;
+static const char *__read_mostly thresh_adj = "standard";
+
+static void do_toggle_guest(unsigned char key, struct cpu_user_regs *regs)
+{
+    if ( upper_thresh_adj == &xenlog_upper_thresh )
+    {
+        upper_thresh_adj = &xenlog_guest_upper_thresh;
+        lower_thresh_adj = &xenlog_guest_lower_thresh;
+        thresh_adj = "guest";
+    }
+    else
+    {
+        upper_thresh_adj = &xenlog_upper_thresh;
+        lower_thresh_adj = &xenlog_lower_thresh;
+        thresh_adj = "standard";
+    }
+    printk("'%c' pressed -> %s log level adjustments enabled\n",
+           key, thresh_adj);
+}
+
+static void do_adj_thresh(unsigned char key)
+{
+    if ( *upper_thresh_adj < *lower_thresh_adj )
+        *upper_thresh_adj = *lower_thresh_adj;
+    printk("'%c' pressed -> %s log level: %s (rate limited %s)\n",
+           key, thresh_adj, loglvl_str(*lower_thresh_adj),
+           loglvl_str(*upper_thresh_adj));
+}
+
+static void do_inc_thresh(unsigned char key, struct cpu_user_regs *regs)
+{
+    ++*lower_thresh_adj;
+    do_adj_thresh(key);
+}
+
+static void do_dec_thresh(unsigned char key, struct cpu_user_regs *regs)
+{
+    if ( *lower_thresh_adj )
+        --*lower_thresh_adj;
+    do_adj_thresh(key);
+}
+
+static struct keyhandler inc_thresh_keyhandler = {
+    .irq_callback = 1,
+    .u.irq_fn = do_inc_thresh,
+    .desc = "increase log level threshold"
+};
+static struct keyhandler dec_thresh_keyhandler = {
+    .irq_callback = 1,
+    .u.irq_fn = do_dec_thresh,
+    .desc = "decrease log level threshold"
+};
+static struct keyhandler toggle_guest_keyhandler = {
+    .irq_callback = 1,
+    .u.irq_fn = do_toggle_guest,
+    .desc = "toggle host/guest log level adjustment"
+};
+
 /*
  * ********************************************************
  * *************** ACCESS TO CONSOLE RING *****************
@@ -834,6 +894,9 @@ void __init console_endboot(void)
         xen_rx = !xen_rx;
 
     register_keyhandler('w', &dump_console_ring_keyhandler);
+    register_keyhandler('+', &inc_thresh_keyhandler);
+    register_keyhandler('-', &dec_thresh_keyhandler);
+    register_keyhandler('G', &toggle_guest_keyhandler);
 
     /* Serial input is directed to DOM0 by default. */
     switch_serial_input();

Attachment: loglvl-adjust.patch
Description: Text document

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