This tedious workaround avoids a 0.26 second pause when using sgabios
(the Serial Graphics Adapter). It's basically a workaround for buggy
code in sgabios, but much easier than fixing the assembler.
---
src/conn-socket.c | 32 +++++++++++++++++++++++++++++++-
1 file changed, 31 insertions(+), 1 deletion(-)
diff --git a/src/conn-socket.c b/src/conn-socket.c
index 5b6b80e..13cb39b 100644
--- a/src/conn-socket.c
+++ b/src/conn-socket.c
@@ -33,6 +33,8 @@
#include <assert.h>
#include <libintl.h>
+#include "ignore-value.h"
+
#include "guestfs.h"
#include "guestfs-internal.h"
@@ -314,6 +316,9 @@ handle_log_message (guestfs_h *g,
{
CLEANUP_FREE char *buf = safe_malloc (g, BUFSIZ);
ssize_t n;
+ const char dsr_request[] = "\033[6n";
+ const char dsr_reply[] = "\033[24;80R";
+ const char dsr_reply_padding[] = "\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b";
/* Carried over from ancient proto.c code. The comment there was:
*
@@ -341,7 +346,32 @@ handle_log_message (guestfs_h *g,
return -1;
}
- /* It's an actual log message, send it upwards. */
+ /* It's an actual log message. */
+
+ /* SGABIOS tries to query the "serial console" for its size using the
+ * ISO/IEC 6429 Device Status Report (ESC [ 6 n). If it doesn't
+ * read anything back, then it unfortunately hangs for 0.26 seconds.
+ * Therefore we detect this situation and send back a fake console
+ * size.
+ */
+ if (memmem (buf, n, dsr_request, sizeof dsr_request - 1) != NULL) {
+ /* Ignore any error from this write, as it's just an optimization.
+ * We can't even be sure that console_sock is a socket or that
+ * it's writable.
+ */
+ ignore_value (write (conn->console_sock, dsr_reply,
+ sizeof dsr_reply - 1));
+ /* Additionally, because of a bug in sgabios, it will still pause
+ * unless you write at least 14 bytes, so we have to pad the
+ * reply. We can't pad with NULs since sgabios's input routine
+ * ignores these, so we have to use some other safe padding
+ * characters. Backspace seems innocuous.
+ */
+ ignore_value (write (conn->console_sock, dsr_reply_padding,
+ sizeof dsr_reply_padding - 1));
+ }
+
+ /* Send it upwards. */
guestfs_int_log_message_callback (g, buf, n);
return 1;
--
2.7.4