Wait a little bit for tty to appear.

There is a race condition that occurs after xend creates a domain.
The console client might be running before the console daemon has
noticed the new domain and setup a pty for it.
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Christian Limpach <Christian.Limpach@cl.cam.ac.uk>

diff --git a/tools/console/client/main.c b/tools/console/client/main.c
index fb0bf25c5e54be2072f3ff3c493f1f7f367fabe3..512e08a8074a80ba1a200b8ae02ce97c919a56ef 100644 (file)
--- a/tools/console/client/main.c
+++ b/tools/console/client/main.c
@@ -176,6 +176,7 @@ int main(int argc, char **argv)
        unsigned int len = 0;
        struct xs_handle *xs;
        char *end;
+       time_t now;
 
        while((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
                switch(ch) {
@@ -215,13 +216,37 @@ int main(int argc, char **argv)
 
        snprintf(path, sizeof(path), "/console/%d/tty", domid);
        str_pty = xs_read(xs, path, &len);
+
        /* FIXME consoled currently does not assume domain-0 doesn't have a
           console which is good when we break domain-0 up.  To keep us
           user friendly, we'll bail out here since no data will ever show
           up on domain-0. */
-       if (domid == 0 || str_pty == NULL) {
+       if (domid == 0) {
+               err(errno, "Could not read tty from store");
+       }
+
+       /* Wait a little bit for tty to appear.  There is a race
+          condition that occurs after xend creates a domain.  This
+          code might be running before consoled has noticed the new
+          domain and setup a pty for it.
+
+          A xenstore watch would slightly improve responsiveness but
+          a timeout would still be needed since we don't want to
+          block forever if given an invalid domain or worse yet, a
+          domain that someone else has connected to. */
+
+       now = time(0);
+       while (str_pty == NULL && (now + 5) > time(0)) {
+               struct timeval tv = { 0, 500 };
+               select(0, NULL, NULL, NULL, &tv); /* pause briefly */
+
+               str_pty = xs_read(xs, path, &len);
+       }
+
+       if (str_pty == NULL) {
                err(errno, "Could not read tty from store");
        }
+
        spty = open(str_pty, O_RDWR | O_NOCTTY);
        if (spty == -1) {
                err(errno, "Could not open tty `%s'", str_pty);