[Libguestfs] [PATCH v4 5/6] conn: Pretend to be a serial terminal, so sgabios doesn't hang.

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 | 34 +++++++++++++++++++++++++++++++++- 1 file changed, 33 insertions(+), 1 deletion(-) diff --git a/src/conn-socket.c b/src/conn-socket.c index 5b6b80e..633946c 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 +346,34 @@ 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) { + debug (g, "responding to serial console Device Status Report"); + + /* 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