bug pass: whole console lines, a quiet SCI, an honest reserve warning

- schinit, schinitd and vgpud build every message from pieces, one
  write() each, so a job starting on another CPU landed mid-line:
  "schinitd: starting vgpud: os.schos.resolvconfno virtio-gpu on this
  machine". They now collect a line and write it at the newline;
  resolvconf's verbose line is one write with its prefix.
- The ACPI SCI registers IRQ_QUIET. A desktop's SCI never fires, and the
  poller took two seconds of silence for a misrouted line ("irq 9:
  nothing has arrived on it") and called the handler every tick. A line
  is only exempt while every handler on it is quiet.
- The loader claims each segment from where the last one's claim ended,
  so two segments sharing a page no longer ask for it twice. When a
  claim is still refused, it names the memory-map entries in the way.
- Stale divesymlink() declaration gone; the kernel.md struct table
  re-measured (inode, buf and file pools grow from slabs now).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01S1giNvrHTrPMPw7V6x1kQ4

cmd/vgpud/main.c

@@ -59,12 +59,42 @@ read_bootmode(void)
     if (n > 0) { b[n] = 0; verbose_boot = (b[0] == 'v'); }
 }
 
+// Whole lines, in one write() each.
+//
+// Every message here is assembled from pieces -- a prefix, a job's label, a
+// number -- and each piece used to be its own write(). The console keeps one
+// write() together, but nothing keeps two of them together, so a job starting
+// on another CPU landed in the middle of the line: "schinitd: starting vgpud:
+// os.schos.resolvconfno virtio-gpu on this machine" was this process and
+// vgpud taking turns a word at a time. The pieces now collect here and go out
+// at the newline.
+static char lbuf[512];
+static int  lbn;
+
+static void
+lflush(void)
+{
+    if (lbn)
+        write(1, lbuf, lbn);
+    lbn = 0;
+}
+
+static void
+emit(const char *s, int n)
+{
+    for (int i = 0; i < n; i++) {
+        lbuf[lbn++] = s[i];
+        if (s[i] == '\n' || lbn == (int)sizeof lbuf)
+            lflush();
+    }
+}
+
 static void
 puts(const char *s)
 {
     int n = 0;
     while (s[n]) n++;
-    write(1, (void *)s, n);
+    emit(s, n);
 }
 
 // Progress, as opposed to news.
@@ -89,10 +119,10 @@ putn(long long v)
 {
     char b[24];
     int i = 0;
-    if (v < 0) { write(1, "-", 1); v = -v; }
-    if (v == 0) { write(1, "0", 1); return; }
+    if (v < 0) { emit("-", 1); v = -v; }
+    if (v == 0) { emit("0", 1); return; }
     while (v > 0) { b[i++] = '0' + (int)(v % 10); v /= 10; }
-    while (i-- > 0) write(1, &b[i], 1);
+    while (i-- > 0) emit(&b[i], 1);
 }
 
 static void
@@ -101,7 +131,7 @@ puthex(unsigned long long v, int digits)
     static const char h[] = "0123456789abcdef";
     char b[17];
     for (int i = digits - 1; i >= 0; i--) { b[i] = h[v & 0xF]; v >>= 4; }
-    write(1, b, digits);
+    emit(b, digits);
 }
 
 static void
@@ -123,6 +153,7 @@ nothing_to_do(const char *why)
     // still an exit the supervisor is told about, which is what stops it being
     // restarted fifteen times in forty-five seconds.
     vputs("vgpud: "); vputs(why); vputs("\n");
+    lflush();
     exit_group(SCHINIT_EXIT_NORESTART);
 }