[Xen-devel] [PATCH] Add timeout to xenconsole to fix race condition in xm create -c

[Anthony Liguori <aliguori@xxxxxxxxxx>]

This should address the problems people are having now.

Wait a little bit for tty to appear.  There is a race condition that 
occurs after xend creates a domain.  Since no event triggers consoled to 
re-examine existing domains, we'll often not see the new pty by the time 
we're here.  Since consoled sleeps for 2 second periods, a 5 second 
timeout should keep us covered.
A xenstore watch isn't much better since we don't want to block forever 
if given an invalid domain or worse yes, a domain that someone else has 
connected to.
Signed-off-by: Anthony Liguori

Regards,

Anthony Liguori

# HG changeset patch
# User Anthony Liguori <aliguori@xxxxxxxxxx>
# Node ID fe6c5ecea53aabedc6b53988da25910e108eafe9
# Parent  551870a55f240791695d30fd7fa92a1bf4e48387
Wait for domain tty to become available.

diff -r 551870a55f24 -r fe6c5ecea53a tools/console/client/main.c
--- a/tools/console/client/main.c       Tue Aug 30 17:53:49 2005
+++ b/tools/console/client/main.c       Tue Aug 30 22:01:01 2005
@@ -176,6 +176,7 @@
        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 @@
 
        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");
        }
+
+       /* FIXME wait a little bit for tty to appear.  There is a race
+          condition that occurs after xend creates a domain.  Since no event
+           triggers consoled to re-examine existing domains, we'll often not
+           see the new pty by the time we're here.  Since consoled sleeps for
+          2 second periods, a 5 second timeout should keep us covered.
+
+          A xenstore watch isn't much better since we don't want to block
+           forever if given an invalid domain or worse yes, 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);

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