qt_poll: split out into separate file and sanitize build

The qt_poll function calls recv to query whether fds marked by select
as readable should be marked POLLIN or POLLHUP in the pollfd structure.
On many platforms such as QNX this requires extra link-time libraries
which were not previously required by QtCore.

While the qt_poll function is intended as a fallback mechanism only for
those platforms which do not implement poll natively, the function was
compiled unconditionally whenever QT_BUILD_INTERNAL was defined, e.g.
in developer builds.

Additionally the function was included on those systems that define poll
in system headers so that configure determines build-time availability,
but do not define _POSIX_POLL > 0 or indicate POSIX:2008 compliance via
either the _POSIX_VERSION or _XOPEN_VERSION macros. On those systems a
sysconf query for _SC_POLL was performed to determine at runtime whether
to call the system poll or qt_poll.

Both of these cases are in fact counterproductive. In the first case the
sole consumer of the function is a single manual unit test. In the
second, to my knowledge no platform requires the runtime fallback.
Despite that, we were forcing an extra dylib in both cases.

Both cases are fixed by 1) moving the implementation into its own file
for the unit test to include and 2) dropping the dynamic fallback if
configure determines availability of poll at compile-time.

This also reverts commit 13777097118c496391d4b9656b95097ac25e4a40, which
added -lsocket for QtCore on QNX.

Change-Id: I2dd10695c5d4cac81b68d2c2558797f3cdabc153
Reviewed-by: James McDonnell <jmcdonnell@qnx.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 220 insertions, 0 deletions

diff --git a/src/corelib/kernel/qpoll.cpp b/src/corelib/kernel/qpoll.cpp
new file mode 100644
index 0000000000..b152518c00
--- /dev/null
+++ b/src/corelib/kernel/qpoll.cpp
@@ -0,0 +1,220 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qcore_unix_p.h"
+
+QT_BEGIN_NAMESPACE
+
+#define QT_POLL_READ_MASK   (POLLIN | POLLRDNORM)
+#define QT_POLL_WRITE_MASK  (POLLOUT | POLLWRNORM | POLLWRBAND)
+#define QT_POLL_EXCEPT_MASK (POLLPRI | POLLRDBAND)
+#define QT_POLL_ERROR_MASK  (POLLERR | POLLNVAL)
+#define QT_POLL_EVENTS_MASK (QT_POLL_READ_MASK | QT_POLL_WRITE_MASK | QT_POLL_EXCEPT_MASK)
+
+static inline int qt_poll_prepare(struct pollfd *fds, nfds_t nfds,
+                                  fd_set *read_fds, fd_set *write_fds, fd_set *except_fds)
+{
+    int max_fd = -1;
+
+    FD_ZERO(read_fds);
+    FD_ZERO(write_fds);
+    FD_ZERO(except_fds);
+
+    for (nfds_t i = 0; i < nfds; i++) {
+        if (fds[i].fd >= FD_SETSIZE) {
+            errno = EINVAL;
+            return -1;
+        }
+
+        if ((fds[i].fd < 0) || (fds[i].revents & QT_POLL_ERROR_MASK))
+            continue;
+
+        if (fds[i].events & QT_POLL_READ_MASK)
+            FD_SET(fds[i].fd, read_fds);
+
+        if (fds[i].events & QT_POLL_WRITE_MASK)
+            FD_SET(fds[i].fd, write_fds);
+
+        if (fds[i].events & QT_POLL_EXCEPT_MASK)
+            FD_SET(fds[i].fd, except_fds);
+
+        if (fds[i].events & QT_POLL_EVENTS_MASK)
+            max_fd = qMax(max_fd, fds[i].fd);
+    }
+
+    return max_fd + 1;
+}
+
+static inline void qt_poll_examine_ready_read(struct pollfd &pfd)
+{
+    int res;
+    char data;
+
+    EINTR_LOOP(res, ::recv(pfd.fd, &data, sizeof(data), MSG_PEEK));
+    const int error = (res < 0) ? errno : 0;
+
+    if (res == 0) {
+        pfd.revents |= POLLHUP;
+    } else if (res > 0 || error == ENOTSOCK || error == ENOTCONN) {
+        pfd.revents |= QT_POLL_READ_MASK & pfd.events;
+    } else {
+        switch (error) {
+        case ESHUTDOWN:
+        case ECONNRESET:
+        case ECONNABORTED:
+        case ENETRESET:
+            pfd.revents |= POLLHUP;
+            break;
+        default:
+            pfd.revents |= POLLERR;
+            break;
+        }
+    }
+}
+
+static inline int qt_poll_sweep(struct pollfd *fds, nfds_t nfds,
+                                fd_set *read_fds, fd_set *write_fds, fd_set *except_fds)
+{
+    int result = 0;
+
+    for (nfds_t i = 0; i < nfds; i++) {
+        if (fds[i].fd < 0)
+            continue;
+
+        if (FD_ISSET(fds[i].fd, read_fds))
+            qt_poll_examine_ready_read(fds[i]);
+
+        if (FD_ISSET(fds[i].fd, write_fds))
+            fds[i].revents |= QT_POLL_WRITE_MASK & fds[i].events;
+
+        if (FD_ISSET(fds[i].fd, except_fds))
+            fds[i].revents |= QT_POLL_EXCEPT_MASK & fds[i].events;
+
+        if (fds[i].revents != 0)
+            result++;
+    }
+
+    return result;
+}
+
+static inline bool qt_poll_is_bad_fd(int fd)
+{
+    int ret;
+    EINTR_LOOP(ret, fcntl(fd, F_GETFD));
+    return (ret == -1 && errno == EBADF);
+}
+
+static inline int qt_poll_mark_bad_fds(struct pollfd *fds, const nfds_t nfds)
+{
+    int n_marked = 0;
+
+    for (nfds_t i = 0; i < nfds; i++) {
+        if (fds[i].fd < 0)
+            continue;
+
+        if (fds[i].revents & QT_POLL_ERROR_MASK)
+            continue;
+
+        if (qt_poll_is_bad_fd(fds[i].fd)) {
+            fds[i].revents |= POLLNVAL;
+            n_marked++;
+        }
+   }
+
+   return n_marked;
+}
+
+int qt_poll(struct pollfd *fds, nfds_t nfds, const struct timespec *timeout_ts)
+{
+    if (!fds && nfds) {
+        errno = EFAULT;
+        return -1;
+    }
+
+    fd_set read_fds, write_fds, except_fds;
+    struct timeval tv, *ptv = 0;
+
+    if (timeout_ts) {
+        tv = timespecToTimeval(*timeout_ts);
+        ptv = &tv;
+    }
+
+    int n_bad_fds = 0;
+
+    for (nfds_t i = 0; i < nfds; i++) {
+        fds[i].revents = 0;
+
+        if (fds[i].fd < 0)
+            continue;
+
+        if (fds[i].events & QT_POLL_EVENTS_MASK)
+            continue;
+
+        if (qt_poll_is_bad_fd(fds[i].fd)) {
+            // Mark bad file descriptors that have no event flags set
+            // here, as we won't be passing them to select below and therefore
+            // need to do the check ourselves
+            fds[i].revents = POLLNVAL;
+            n_bad_fds++;
+        }
+    }
+
+    forever {
+        const int max_fd = qt_poll_prepare(fds, nfds, &read_fds, &write_fds, &except_fds);
+
+        if (max_fd < 0)
+            return max_fd;
+
+        if (n_bad_fds > 0) {
+            tv.tv_sec = 0;
+            tv.tv_usec = 0;
+            ptv = &tv;
+        }
+
+        const int ret = ::select(max_fd, &read_fds, &write_fds, &except_fds, ptv);
+
+        if (ret == 0)
+            return n_bad_fds;
+
+        if (ret > 0)
+            return qt_poll_sweep(fds, nfds, &read_fds, &write_fds, &except_fds);
+
+        if (errno != EBADF)
+            return -1;
+
+        // We have at least one bad file descriptor that we waited on, find out which and try again
+        n_bad_fds += qt_poll_mark_bad_fds(fds, nfds);
+    }
+}
+
+QT_END_NAMESPACE