Re: [Xen-devel] [PATCH v3 6/6] tools/libxl: Adjust datacopiers POLLHUP handling when the fd is also readable

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Mon, 2015-03-16 at 13:29 +0000, Ross Lagerwall wrote:
> From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> 
> 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
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Ian Campbell <Ian.Campbell@xxxxxxxxxx>



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