io: add QIOChannelCommand class

Add a QIOChannel subclass that is capable of performing I/O
to/from a separate process, via a pair of pipes. The command
can be used for unidirectional or bi-directional I/O.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

2 files changed, 358 insertions, 0 deletions

diff --git a/io/Makefile.objs b/io/Makefile.objs
index e3771b1ac1..1a58ccb5c2 100644
--- a/io/Makefile.objs
+++ b/io/Makefile.objs
@@ -1,4 +1,5 @@
 io-obj-y = channel.o
+io-obj-y += channel-command.o
 io-obj-y += channel-file.o
 io-obj-y += channel-socket.o
 io-obj-y += channel-tls.o
diff --git a/io/channel-command.c b/io/channel-command.c
new file mode 100644
index 0000000000..598fdab5a3
--- /dev/null
+++ b/io/channel-command.c
@@ -0,0 +1,357 @@
+/*
+ * QEMU I/O channels external command driver
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "io/channel-command.h"
+#include "io/channel-watch.h"
+#include "qemu/sockets.h"
+#include "trace.h"
+
+
+QIOChannelCommand *
+qio_channel_command_new_pid(int writefd,
+                            int readfd,
+                            pid_t pid)
+{
+    QIOChannelCommand *ioc;
+
+    ioc = QIO_CHANNEL_COMMAND(object_new(TYPE_QIO_CHANNEL_COMMAND));
+
+    ioc->readfd = readfd;
+    ioc->writefd = writefd;
+    ioc->pid = pid;
+
+    trace_qio_channel_command_new_pid(ioc, writefd, readfd, pid);
+    return ioc;
+}
+
+
+#ifndef WIN32
+QIOChannelCommand *
+qio_channel_command_new_spawn(const char *const argv[],
+                              int flags,
+                              Error **errp)
+{
+    pid_t pid = -1;
+    int stdinfd[2] = { -1, -1 };
+    int stdoutfd[2] = { -1, -1 };
+    int devnull = -1;
+    bool stdinnull = false, stdoutnull = false;
+    QIOChannelCommand *ioc;
+
+    flags = flags & O_ACCMODE;
+
+    if (flags == O_RDONLY) {
+        stdinnull = true;
+    }
+    if (flags == O_WRONLY) {
+        stdoutnull = true;
+    }
+
+    if (stdinnull || stdoutnull) {
+        devnull = open("/dev/null", O_RDWR);
+        if (!devnull) {
+            error_setg_errno(errp, errno,
+                             "Unable to open /dev/null");
+            goto error;
+        }
+    }
+
+    if ((!stdinnull && pipe(stdinfd) < 0) ||
+        (!stdoutnull && pipe(stdoutfd) < 0)) {
+        error_setg_errno(errp, errno,
+                         "Unable to open pipe");
+        goto error;
+    }
+
+    pid = qemu_fork(errp);
+    if (pid < 0) {
+        goto error;
+    }
+
+    if (pid == 0) { /* child */
+        dup2(stdinnull ? devnull : stdinfd[0], STDIN_FILENO);
+        dup2(stdoutnull ? devnull : stdoutfd[1], STDOUT_FILENO);
+        /* Leave stderr connected to qemu's stderr */
+
+        if (!stdinnull) {
+            close(stdinfd[0]);
+            close(stdinfd[1]);
+        }
+        if (!stdoutnull) {
+            close(stdoutfd[0]);
+            close(stdoutfd[1]);
+        }
+
+        execv(argv[0], (char * const *)argv);
+        _exit(1);
+    }
+
+    if (!stdinnull) {
+        close(stdinfd[0]);
+    }
+    if (!stdoutnull) {
+        close(stdoutfd[1]);
+    }
+
+    ioc = qio_channel_command_new_pid(stdinnull ? devnull : stdinfd[1],
+                                      stdoutnull ? devnull : stdoutfd[0],
+                                      pid);
+    trace_qio_channel_command_new_spawn(ioc, argv[0], flags);
+    return ioc;
+
+ error:
+    if (stdinfd[0] != -1) {
+        close(stdinfd[0]);
+    }
+    if (stdinfd[1] != -1) {
+        close(stdinfd[1]);
+    }
+    if (stdoutfd[0] != -1) {
+        close(stdoutfd[0]);
+    }
+    if (stdoutfd[1] != -1) {
+        close(stdoutfd[1]);
+    }
+    return NULL;
+}
+
+#else /* WIN32 */
+QIOChannelCommand *
+qio_channel_command_new_spawn(const char *const argv[],
+                              int flags,
+                              Error **errp)
+{
+    error_setg_errno(errp, ENOSYS,
+                     "Command spawn not supported on this platform");
+    return NULL;
+}
+#endif /* WIN32 */
+
+#ifndef WIN32
+static int qio_channel_command_abort(QIOChannelCommand *ioc,
+                                     Error **errp)
+{
+    pid_t ret;
+    int status;
+    int step = 0;
+
+    /* See if intermediate process has exited; if not, try a nice
+     * SIGTERM followed by a more severe SIGKILL.
+     */
+ rewait:
+    trace_qio_channel_command_abort(ioc, ioc->pid);
+    ret = waitpid(ioc->pid, &status, WNOHANG);
+    trace_qio_channel_command_wait(ioc, ioc->pid, ret, status);
+    if (ret == (pid_t)-1) {
+        if (errno == EINTR) {
+            goto rewait;
+        } else {
+            error_setg_errno(errp, errno,
+                             "Cannot wait on pid %llu",
+                             (unsigned long long)ioc->pid);
+            return -1;
+        }
+    } else if (ret == 0) {
+        if (step == 0) {
+            kill(ioc->pid, SIGTERM);
+        } else if (step == 1) {
+            kill(ioc->pid, SIGKILL);
+        } else {
+            error_setg(errp,
+                       "Process %llu refused to die",
+                       (unsigned long long)ioc->pid);
+            return -1;
+        }
+        usleep(10 * 1000);
+        goto rewait;
+    }
+
+    return 0;
+}
+#endif /* ! WIN32 */
+
+
+static void qio_channel_command_init(Object *obj)
+{
+    QIOChannelCommand *ioc = QIO_CHANNEL_COMMAND(obj);
+    ioc->readfd = -1;
+    ioc->writefd = -1;
+    ioc->pid = -1;
+}
+
+static void qio_channel_command_finalize(Object *obj)
+{
+    QIOChannelCommand *ioc = QIO_CHANNEL_COMMAND(obj);
+    if (ioc->readfd != -1) {
+        close(ioc->readfd);
+        ioc->readfd = -1;
+    }
+    if (ioc->writefd != -1) {
+        close(ioc->writefd);
+        ioc->writefd = -1;
+    }
+    if (ioc->pid > 0) {
+#ifndef WIN32
+        qio_channel_command_abort(ioc, NULL);
+#endif
+    }
+}
+
+
+static ssize_t qio_channel_command_readv(QIOChannel *ioc,
+                                         const struct iovec *iov,
+                                         size_t niov,
+                                         int **fds,
+                                         size_t *nfds,
+                                         Error **errp)
+{
+    QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = readv(cioc->readfd, iov, niov);
+    if (ret < 0) {
+        if (errno == EAGAIN ||
+            errno == EWOULDBLOCK) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+
+        error_setg_errno(errp, errno,
+                         "Unable to read from command");
+        return -1;
+    }
+
+    return ret;
+}
+
+static ssize_t qio_channel_command_writev(QIOChannel *ioc,
+                                          const struct iovec *iov,
+                                          size_t niov,
+                                          int *fds,
+                                          size_t nfds,
+                                          Error **errp)
+{
+    QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
+    ssize_t ret;
+
+ retry:
+    ret = writev(cioc->writefd, iov, niov);
+    if (ret <= 0) {
+        if (errno == EAGAIN ||
+            errno == EWOULDBLOCK) {
+            return QIO_CHANNEL_ERR_BLOCK;
+        }
+        if (errno == EINTR) {
+            goto retry;
+        }
+        error_setg_errno(errp, errno, "%s",
+                         "Unable to write to command");
+        return -1;
+    }
+    return ret;
+}
+
+static int qio_channel_command_set_blocking(QIOChannel *ioc,
+                                            bool enabled,
+                                            Error **errp)
+{
+    QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
+
+    if (enabled) {
+        qemu_set_block(cioc->writefd);
+        qemu_set_block(cioc->readfd);
+    } else {
+        qemu_set_nonblock(cioc->writefd);
+        qemu_set_nonblock(cioc->readfd);
+    }
+
+    return 0;
+}
+
+
+static int qio_channel_command_close(QIOChannel *ioc,
+                                     Error **errp)
+{
+    QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
+    int rv = 0;
+
+    /* We close FDs before killing, because that
+     * gives a better chance of clean shutdown
+     */
+    if (close(cioc->writefd) < 0) {
+        rv = -1;
+    }
+    if (close(cioc->readfd) < 0) {
+        rv = -1;
+    }
+#ifndef WIN32
+    if (qio_channel_command_abort(cioc, errp) < 0) {
+        return -1;
+    }
+#endif
+    if (rv < 0) {
+        error_setg_errno(errp, errno, "%s",
+                         "Unable to close command");
+    }
+    return rv;
+}
+
+
+static GSource *qio_channel_command_create_watch(QIOChannel *ioc,
+                                                 GIOCondition condition)
+{
+    QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
+    return qio_channel_create_fd_pair_watch(ioc,
+                                            cioc->readfd,
+                                            cioc->writefd,
+                                            condition);
+}
+
+
+static void qio_channel_command_class_init(ObjectClass *klass,
+                                           void *class_data G_GNUC_UNUSED)
+{
+    QIOChannelClass *ioc_klass = QIO_CHANNEL_CLASS(klass);
+
+    ioc_klass->io_writev = qio_channel_command_writev;
+    ioc_klass->io_readv = qio_channel_command_readv;
+    ioc_klass->io_set_blocking = qio_channel_command_set_blocking;
+    ioc_klass->io_close = qio_channel_command_close;
+    ioc_klass->io_create_watch = qio_channel_command_create_watch;
+}
+
+static const TypeInfo qio_channel_command_info = {
+    .parent = TYPE_QIO_CHANNEL,
+    .name = TYPE_QIO_CHANNEL_COMMAND,
+    .instance_size = sizeof(QIOChannelCommand),
+    .instance_init = qio_channel_command_init,
+    .instance_finalize = qio_channel_command_finalize,
+    .class_init = qio_channel_command_class_init,
+};
+
+static void qio_channel_command_register_types(void)
+{
+    type_register_static(&qio_channel_command_info);
+}
+
+type_init(qio_channel_command_register_types);