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From 4f88b55bfad9d72675ef09480dd4d8ad96047842 Mon Sep 17 00:00:00 2001
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From: "Richard W.M. Jones" <rjones@redhat.com>
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Date: Sun, 20 Mar 2016 15:50:31 +0000
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Subject: [PATCH] conn: Pretend to be a serial terminal, so sgabios doesn't
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hang.
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This tedious workaround avoids a 0.26 second pause when using sgabios
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(the Serial Graphics Adapter). It's basically a workaround for buggy
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code in sgabios, but much easier than fixing the assembler.
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(cherry picked from commit cd578510197eb87abf996a3a050779806682e83f)
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---
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src/conn-socket.c | 34 +++++++++++++++++++++++++++++++++-
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1 file changed, 33 insertions(+), 1 deletion(-)
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diff --git a/src/conn-socket.c b/src/conn-socket.c
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index 9db0bfd..8a4b9d0 100644
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--- a/src/conn-socket.c
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+++ b/src/conn-socket.c
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@@ -33,6 +33,8 @@
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#include <assert.h>
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#include <libintl.h>
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+#include "ignore-value.h"
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+
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#include "guestfs.h"
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#include "guestfs-internal.h"
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@@ -314,6 +316,9 @@ handle_log_message (guestfs_h *g,
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{
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char buf[BUFSIZ];
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ssize_t n;
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+ const char dsr_request[] = "\033[6n";
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+ const char dsr_reply[] = "\033[24;80R";
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+ const char dsr_reply_padding[] = "\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b\b";
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/* Carried over from ancient proto.c code. The comment there was:
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*
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@@ -341,7 +346,34 @@ handle_log_message (guestfs_h *g,
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return -1;
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}
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- /* It's an actual log message, send it upwards. */
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+ /* It's an actual log message. */
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+
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+ /* SGABIOS tries to query the "serial console" for its size using the
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+ * ISO/IEC 6429 Device Status Report (ESC [ 6 n). If it doesn't
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+ * read anything back, then it unfortunately hangs for 0.26 seconds.
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+ * Therefore we detect this situation and send back a fake console
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+ * size.
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+ */
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+ if (memmem (buf, n, dsr_request, sizeof dsr_request - 1) != NULL) {
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+ debug (g, "responding to serial console Device Status Report");
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+
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+ /* Ignore any error from this write, as it's just an optimization.
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+ * We can't even be sure that console_sock is a socket or that
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+ * it's writable.
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+ */
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+ ignore_value (write (conn->console_sock, dsr_reply,
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+ sizeof dsr_reply - 1));
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+ /* Additionally, because of a bug in sgabios, it will still pause
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+ * unless you write at least 14 bytes, so we have to pad the
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+ * reply. We can't pad with NULs since sgabios's input routine
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+ * ignores these, so we have to use some other safe padding
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+ * characters. Backspace seems innocuous.
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+ */
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+ ignore_value (write (conn->console_sock, dsr_reply_padding,
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+ sizeof dsr_reply_padding - 1));
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+ }
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+
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+ /* Send it upwards. */
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guestfs_int_log_message_callback (g, buf, n);
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return 1;
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--
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1.8.3.1
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