[Xen-changelog] [xen master] Revert "tools/libxl: Adjust datacopiers POLLHUP handling when the fd is also readable"

[patchbot@xxxxxxx]

commit 1a362e2a36dd06d748531917d07dbab42fe0eae3
Author:     Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
AuthorDate: Thu Apr 2 15:32:22 2015 +0100
Commit:     Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CommitDate: Thu Apr 2 16:10:03 2015 +0100

    Revert "tools/libxl: Adjust datacopiers POLLHUP handling when the fd is 
also readable"

    The bootloader code is relying on detecting POLLHUP, and 7e9ec50b
    breaks that.  7e9ec50b, when handling a pty master, violates the
    specification of the datacopier interface (as defined).

    When the bootloader exits, several things change, all at once:
     (a) The master pty fd (held by libxl) starts to signal POLLHUP
        and maybe also POLLIN.
     (b) The child exits (so that the SIGCHLD self-pipe signals POLLIN,
        which will be handled by the libxl child process code.
     (c) reads on the master pty fd start to return EOF

    From the point of view of the datacopier these might happen in any
    order.  I think there is a latent bug with (c), which I will discuss
    later in this email.

    In a recent bug report from a FreeBSD installation, the datacopier
    gets told about (a) before (b).  But 7e9ec50b filters the POLLHUP out,
    so that the dc signals eof rather than hup.  As a result in
    bootloader_copyfail we take the error path.

    This reverts commit 7e9ec50b0535bf2630da9d279a060775817d136d.

    Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
    CC: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
    CC: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxl/libxl_aoutils.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index da102a0..3942634 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -205,9 +205,6 @@ static void datacopier_readable(libxl__egc *egc, 
libxl__ev_fd *ev,
     libxl__datacopier_state *dc = CONTAINER_OF(ev, *dc, toread);
     STATE_AO_GC(dc->ao);

-    if ((revents & (POLLHUP|POLLIN)) == (POLLHUP|POLLIN))
-        revents &= ~POLLHUP;
-
     if (datacopier_pollhup_handled(egc, dc, revents, 0))
         return;

--
generated by git-patchbot for /home/xen/git/xen.git#master

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