From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?windows-1252?Q?Roger_Pau_Monn=E9?= <roger.pau@citrix.com>
Subject: Re: [PATCH v3 6/6] tools/libxl: Adjust datacopiers
 POLLHUP handling when the fd is also readable
Date: Thu, 26 Mar 2015 16:20:08 +0100
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References: <1426512594-11585-1-git-send-email-ross.lagerwall@citrix.com>
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To: Ross Lagerwall <ross.lagerwall@citrix.com>, xen-devel@lists.xen.org
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>, Wei Liu <wei.liu2@citrix.com>
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El 16/03/15 a les 14.29, Ross Lagerwall ha escrit:
> From: Andrew Cooper <andrew.cooper3@citrix.com>
> 
> POLLHUP|POLLIN is a valid revent to receive when there is readable data in a
> pipe, but the writable fd has been closed.  This occurs in migration v2 when
> the legacy conversion process (which transforms the data inline) completes and
> exits successfully.
> 
> In the case that there is data to read, suppress the POLLHUP.  POSIX states
> that the hangup state is latched[1], which means it will reoccur on subsequent
> poll() calls.  The datacopier is thus provided the opportunity to read until
> EOF, if possible.
> 
> A POLLHUP on its own is treated exactly as before, indicating a different
> error with the fd.
> 
> [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html

This patch breaks booting pygrub guests on FreeBSD, it seems to trigger 
some kind of error when pygrub exits:

libxl: error: libxl_bootloader.c:596:bootloader_copyfail: unexpected eof copying bootloader output
libxl: error: libxl_create.c:1129:domcreate_rebuild_done: cannot (re-)build domain: -3

I will try to look into it, have you tested if the same happens on 
Linux?

Roger.