[Xen-changelog] [xen master] libxl: events: Pass correct nfds to poll

[patchbot@xxxxxxx]

commit 4b01bd9d3e4d9933d282ad2a36da9cc110a4a1a9
Author:     Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
AuthorDate: Tue Jan 21 18:45:29 2014 +0000
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Tue Jan 28 11:21:48 2014 +0000

    libxl: events: Pass correct nfds to poll
    
    libxl_event.c:eventloop_iteration would pass the allocated pollfds
    array size, rather than the used size, to poll (and to
    afterpoll_internal).
    
    The effect is that if the number of fds to poll on reduces, libxl will
    poll on stale entries.  Because of the way the return value from poll
    is processed these stale entries are often harmless because any events
    coming back from poll ignored by libxl.  However, it could cause
    malfunctions:
    
    It could result in unwanted SIGTTIN/SIGTTOU/SIGPIPE, for example, if
    the fd has been reused to refer to an object which can generate those
    signals.  Alternatively, it could result in libxl spinning if the
    stale entry refers to an fd which happens now to be ready for the
    previously-requested operation.
    
    I have tested this with a localhost migration and inspected the strace
    output.
    
    Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
    Cc: Jim Fehlig <jfehlig@xxxxxxxx>
    Cc: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
    Acked-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
---
 tools/libxl/libxl_event.c |    9 ++++-----
 1 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index bdef7ac..1c48fee 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -1386,7 +1386,7 @@ static int eventloop_iteration(libxl__egc *egc, 
libxl__poller *poller) {
      * can unlock it when it polls.
      */
     EGC_GC;
-    int rc;
+    int rc, nfds;
     struct timeval now;
     
     rc = libxl__gettimeofday(gc, &now);
@@ -1395,7 +1395,7 @@ static int eventloop_iteration(libxl__egc *egc, 
libxl__poller *poller) {
     int timeout;
 
     for (;;) {
-        int nfds = poller->fd_polls_allocd;
+        nfds = poller->fd_polls_allocd;
         timeout = -1;
         rc = beforepoll_internal(gc, poller, &nfds, poller->fd_polls,
                                  &timeout, now);
@@ -1413,7 +1413,7 @@ static int eventloop_iteration(libxl__egc *egc, 
libxl__poller *poller) {
     }
 
     CTX_UNLOCK;
-    rc = poll(poller->fd_polls, poller->fd_polls_allocd, timeout);
+    rc = poll(poller->fd_polls, nfds, timeout);
     CTX_LOCK;
 
     if (rc < 0) {
@@ -1428,8 +1428,7 @@ static int eventloop_iteration(libxl__egc *egc, 
libxl__poller *poller) {
     rc = libxl__gettimeofday(gc, &now);
     if (rc) goto out;
 
-    afterpoll_internal(egc, poller,
-                       poller->fd_polls_allocd, poller->fd_polls, now);
+    afterpoll_internal(egc, poller, nfds, poller->fd_polls, now);
 
     rc = 0;
  out:
--
generated by git-patchbot for /home/xen/git/xen.git#master

_______________________________________________
Xen-changelog mailing list
Xen-changelog@xxxxxxxxxxxxx
http://lists.xensource.com/xen-changelog