On Tue, Apr 07, 2015 at 02:05:28PM +0100, Ian Jackson wrote: > Some operating systems (including Linux and FreeBSD[1]) signal not > (only) POLLIN when a reading pipe reaches EOF, but POLLHUP (with or > without POLLIN). This is permitted[2]. The implications are that in > the general case it is not possible to determine whether POLLHUP > indicates an error or simply eof without attempting a read. > > Datacopiers mishandle this, because they always treat POLLHUP > exceptionally (either reporting it via callback_pollhup, or treating > it as an error). datacopiers reading from pipes on such OSs can fail > (perhaps leaving some data unprocessed) rather than completing > successfully. > > [1] http://www.greenend.org.uk/rjk/tech/poll.html > [2] http://pubs.opengroup.org/onlinepubs/9699919799/functions/poll.html > > Distinguishing POLLHUP is needed for pty fds, but most callers in > libxl do not care about POLLHUP except as an error or eof condition. > > So change the datacopier semantics so that if callback_pollhup is not > specified we treat POLLHUP almost like POLLIN. The difference is that > if we get HUP from poll, but EWOULDBLOCK from read, we must signal an > error ratehr than attempting the read again. > > This fixes the problem which 7e9ec50b0535 was aimed at. > > Signed-off-by: Ian Jackson <ian.jack...@eu.citrix.com> > CC: Ian Campbell <ian.campb...@citrix.com> > CC: Andrew Cooper <andrew.coop...@citrix.com> > CC: Roger Pau Monné <roger....@citrix.com> > CC: Ross Lagerwall <ross.lagerw...@citrix.com> > CC: Wei Liu <wei.l...@citrix.com>
The code matches documents and commit log so: Acked-by: Wei Liu <wei.l...@citrix.com> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
