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From:   Gal Ben Haim <gbenhaim@augury.com>
Date:   Thu, 15 Nov 2018 21:34:23 +0200
Message-ID: <CAHotPr9A7A6Rf0+JgQN6nAiXYDGp6QiaPeXP6vyomXeR4F57Cw@mail.gmail.com>
Subject: Re: [PATCH BlueZ] shared/io-mainloop: Try to write to the pipe only
 if there are readers
To:     Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     linux-bluetooth@vger.kernel.org
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Sender: linux-bluetooth-owner@vger.kernel.org
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doesn't my first patch of ignoring SIGPIPE simplify this? errno of the
write op will be EPIPE..
I can move it to main.c
On Thu, Nov 15, 2018 at 2:38 PM Luiz Augusto von Dentz
<luiz.dentz@gmail.com> wrote:
>
> Hi Gal,
> On Thu, Nov 15, 2018 at 1:55 PM Gal Ben-Haim <gbenhaim@augury.com> wrote:
> >
> > bluetoothd receives a SIGPIPE and terminates if writing to a pipe that
> > was acquired by AcquireNotify and there are no readers. it can be
> > reproduced by terminating the reader process without closing the reader
> > end of the pipe.
> >
> > poll is used to check for a POLLRDHUP event before write and an EPIPE
> > error is returned if the peer closed its end of the pipe.
> > ---
> >  src/shared/io-mainloop.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/src/shared/io-mainloop.c b/src/shared/io-mainloop.c
> > index 2306c3479..4a70449fc 100644
> > --- a/src/shared/io-mainloop.c
> > +++ b/src/shared/io-mainloop.c
> > @@ -27,6 +27,7 @@
> >
> >  #include <unistd.h>
> >  #include <errno.h>
> > +#include <poll.h>
> >  #include <sys/socket.h>
> >
> >  #include "src/shared/mainloop.h"
> > @@ -305,7 +306,14 @@ ssize_t io_send(struct io *io, const struct iovec *iov, int iovcnt)
> >         if (!io || io->fd < 0)
> >                 return -ENOTCONN;
> >
> > +       struct pollfd fds[1];
> > +       fds[0].fd = io->fd;
> > +       fds[0].events = POLLRDHUP;
> >         do {
> > +               if (poll(fds, 1, 0) > 0 && fds[0].revents & POLLRDHUP > 0) {
> > +                       return -EPIPE;
> > +               }
> > +
> >                 ret = writev(io->fd, iov, iovcnt);
> >         } while (ret < 0 && errno == EINTR);
> >
> > --
> > 2.19.1
>
> We normally do it a bit differently, we setup a write handler using
> io_set_write_handler which informs when the fd is writable, otherwise
> we maybe polling twice here since the user of the io may already be
> using that mechanism. That said you are actually checking for HUP
> which is something done io_set_disconnect_handler, which is already in
> use. I suspect to really get this done cleanly we should perhaps use
> MSG_NOSIGNAL when trying to write.
>
> --
> Luiz Augusto von Dentz