session: fix use after free of session->devs as reported by valgrind

[libsigrok.git] / src / session.c

/*
 * This file is part of the libsigrok project.
 *
 * Copyright (C) 2010-2012 Bert Vermeulen <bert@biot.com>
 * Copyright (C) 2015 Daniel Elstner <daniel.kitta@gmail.com>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <config.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <glib.h>
#include <libsigrok/libsigrok.h>
#include "libsigrok-internal.h"

/** @cond PRIVATE */
#define LOG_PREFIX "session"
/** @endcond */

/**
 * @file
 *
 * Creating, using, or destroying libsigrok sessions.
 */

/**
 * @defgroup grp_session Session handling
 *
 * Creating, using, or destroying libsigrok sessions.
 *
 * @{
 */

struct datafeed_callback {
        sr_datafeed_callback cb;
        void *cb_data;
};

/** Custom GLib event source for generic descriptor I/O.
 * @see https://developer.gnome.org/glib/stable/glib-The-Main-Event-Loop.html
 * @internal
 */
struct fd_source {
        GSource base;

        int64_t timeout_us;
        int64_t due_us;

        /* Meta-data needed to keep track of installed sources */
        struct sr_session *session;
        void *key;

        GPollFD pollfd;
};

/** FD event source prepare() method.
 * This is called immediately before poll().
 */
static gboolean fd_source_prepare(GSource *source, int *timeout)
{
        int64_t now_us;
        struct fd_source *fsource;
        int remaining_ms;

        fsource = (struct fd_source *)source;

        if (fsource->timeout_us >= 0) {
                now_us = g_source_get_time(source);

                if (fsource->due_us == 0) {
                        /* First-time initialization of the expiration time */
                        fsource->due_us = now_us + fsource->timeout_us;
                }
                remaining_ms = (MAX(0, fsource->due_us - now_us) + 999) / 1000;
        } else {
                remaining_ms = -1;
        }
        *timeout = remaining_ms;

        return (remaining_ms == 0);
}

/** FD event source check() method.
 * This is called after poll() returns to check whether an event fired.
 */
static gboolean fd_source_check(GSource *source)
{
        struct fd_source *fsource;
        unsigned int revents;

        fsource = (struct fd_source *)source;
        revents = fsource->pollfd.revents;

        return (revents != 0 || (fsource->timeout_us >= 0
                        && fsource->due_us <= g_source_get_time(source)));
}

/** FD event source dispatch() method.
 * This is called if either prepare() or check() returned TRUE.
 */
static gboolean fd_source_dispatch(GSource *source,
                GSourceFunc callback, void *user_data)
{
        struct fd_source *fsource;
        unsigned int revents;
        gboolean keep;

        fsource = (struct fd_source *)source;
        revents = fsource->pollfd.revents;

        if (!callback) {
                sr_err("Callback not set, cannot dispatch event.");
                return G_SOURCE_REMOVE;
        }
        keep = (*(sr_receive_data_callback)callback)
                        (fsource->pollfd.fd, revents, user_data);

        if (fsource->timeout_us >= 0 && G_LIKELY(keep)
                        && G_LIKELY(!g_source_is_destroyed(source)))
                fsource->due_us = g_source_get_time(source)
                                + fsource->timeout_us;
        return keep;
}

/** FD event source finalize() method.
 */
static void fd_source_finalize(GSource *source)
{
        struct fd_source *fsource;

        fsource = (struct fd_source *)source;

        sr_dbg("%s: key %p", __func__, fsource->key);

        sr_session_source_destroyed(fsource->session, fsource->key, source);
}

/** Create an event source for I/O on a file descriptor.
 *
 * In order to maintain API compatibility, this event source also doubles
 * as a timer event source.
 *
 * @param session The session the event source belongs to.
 * @param key The key used to identify this source.
 * @param fd The file descriptor or HANDLE.
 * @param timeout_ms The timeout interval in ms, or -1 to wait indefinitely.
 * @return A new event source object, or NULL on failure.
 */
static GSource *fd_source_new(struct sr_session *session, void *key,
                gintptr fd, int events, int timeout_ms)
{
        static GSourceFuncs fd_source_funcs = {
                .prepare  = &fd_source_prepare,
                .check    = &fd_source_check,
                .dispatch = &fd_source_dispatch,
                .finalize = &fd_source_finalize
        };
        GSource *source;
        struct fd_source *fsource;

        source = g_source_new(&fd_source_funcs, sizeof(struct fd_source));
        fsource = (struct fd_source *)source;

        g_source_set_name(source, (fd < 0) ? "timer" : "fd");

        if (timeout_ms >= 0) {
                fsource->timeout_us = 1000 * (int64_t)timeout_ms;
                fsource->due_us = 0;
        } else {
                fsource->timeout_us = -1;
                fsource->due_us = INT64_MAX;
        }
        fsource->session = session;
        fsource->key = key;

        fsource->pollfd.fd = fd;
        fsource->pollfd.events = events;
        fsource->pollfd.revents = 0;

        if (fd >= 0)
                g_source_add_poll(source, &fsource->pollfd);

        return source;
}

/**
 * Create a new session.
 *
 * @param ctx         The context in which to create the new session.
 * @param new_session This will contain a pointer to the newly created
 *                    session if the return value is SR_OK, otherwise the value
 *                    is undefined and should not be used. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.4.0
 */
SR_API int sr_session_new(struct sr_context *ctx,
                struct sr_session **new_session)
{
        struct sr_session *session;

        if (!new_session)
                return SR_ERR_ARG;

        session = g_malloc0(sizeof(struct sr_session));

        session->ctx = ctx;

        g_mutex_init(&session->main_mutex);

        /* To maintain API compatibility, we need a lookup table
         * which maps poll_object IDs to GSource* pointers.
         */
        session->event_sources = g_hash_table_new(NULL, NULL);

        *new_session = session;

        return SR_OK;
}

/**
 * Destroy a session.
 * This frees up all memory used by the session.
 *
 * @param session The session to destroy. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_destroy(struct sr_session *session)
{
        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        sr_session_dev_remove_all(session);
        g_slist_free_full(session->owned_devs, (GDestroyNotify)sr_dev_inst_free);

        g_hash_table_unref(session->event_sources);

        g_mutex_clear(&session->main_mutex);

        g_free(session);

        return SR_OK;
}

/**
 * Remove all the devices from a session.
 *
 * The session itself (i.e., the struct sr_session) is not free'd and still
 * exists after this function returns.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_BUG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_dev_remove_all(struct sr_session *session)
{
        struct sr_dev_inst *sdi;
        GSList *l;

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        for (l = session->devs; l; l = l->next) {
                sdi = (struct sr_dev_inst *) l->data;
                sdi->session = NULL;
        }

        g_slist_free(session->devs);
        session->devs = NULL;

        return SR_OK;
}

/**
 * Add a device instance to a session.
 *
 * @param session The session to add to. Must not be NULL.
 * @param sdi The device instance to add to a session. Must not
 *            be NULL. Also, sdi->driver and sdi->driver->dev_open must
 *            not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.4.0
 */
SR_API int sr_session_dev_add(struct sr_session *session,
                struct sr_dev_inst *sdi)
{
        int ret;

        if (!sdi) {
                sr_err("%s: sdi was NULL", __func__);
                return SR_ERR_ARG;
        }

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        /* If sdi->session is not NULL, the device is already in this or
         * another session. */
        if (sdi->session) {
                sr_err("%s: already assigned to session", __func__);
                return SR_ERR_ARG;
        }

        /* If sdi->driver is NULL, this is a virtual device. */
        if (!sdi->driver) {
                /* Just add the device, don't run dev_open(). */
                session->devs = g_slist_append(session->devs, sdi);
                sdi->session = session;
                return SR_OK;
        }

        /* sdi->driver is non-NULL (i.e. we have a real device). */
        if (!sdi->driver->dev_open) {
                sr_err("%s: sdi->driver->dev_open was NULL", __func__);
                return SR_ERR_BUG;
        }

        session->devs = g_slist_append(session->devs, sdi);
        sdi->session = session;

        /* TODO: This is invalid if the session runs in a different thread.
         * The usage semantics and restrictions need to be documented.
         */
        if (session->running) {
                /* Adding a device to a running session. Commit settings
                 * and start acquisition on that device now. */
                if ((ret = sr_config_commit(sdi)) != SR_OK) {
                        sr_err("Failed to commit device settings before "
                               "starting acquisition in running session (%s)",
                               sr_strerror(ret));
                        return ret;
                }
                if ((ret = sdi->driver->dev_acquisition_start(sdi,
                                        sdi)) != SR_OK) {
                        sr_err("Failed to start acquisition of device in "
                               "running session (%s)", sr_strerror(ret));
                        return ret;
                }
        }

        return SR_OK;
}

/**
 * List all device instances attached to a session.
 *
 * @param session The session to use. Must not be NULL.
 * @param devlist A pointer where the device instance list will be
 *                stored on return. If no devices are in the session,
 *                this will be NULL. Each element in the list points
 *                to a struct sr_dev_inst *.
 *                The list must be freed by the caller, but not the
 *                elements pointed to.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.4.0
 */
SR_API int sr_session_dev_list(struct sr_session *session, GSList **devlist)
{
        if (!session)
                return SR_ERR_ARG;

        if (!devlist)
                return SR_ERR_ARG;

        *devlist = g_slist_copy(session->devs);

        return SR_OK;
}

/**
 * Remove a device instance from a session.
 *
 * @param session The session to remove from. Must not be NULL.
 * @param sdi The device instance to remove from a session. Must not
 *            be NULL. Also, sdi->driver and sdi->driver->dev_open must
 *            not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.4.0
 */
SR_API int sr_session_dev_remove(struct sr_session *session,
                struct sr_dev_inst *sdi)
{
        if (!sdi) {
                sr_err("%s: sdi was NULL", __func__);
                return SR_ERR_ARG;
        }

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        /* If sdi->session is not session, the device is not in this
         * session. */
        if (sdi->session != session) {
                sr_err("%s: not assigned to this session", __func__);
                return SR_ERR_ARG;
        }

        session->devs = g_slist_remove(session->devs, sdi);
        sdi->session = NULL;

        return SR_OK;
}

/**
 * Remove all datafeed callbacks in a session.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_datafeed_callback_remove_all(struct sr_session *session)
{
        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        g_slist_free_full(session->datafeed_callbacks, g_free);
        session->datafeed_callbacks = NULL;

        return SR_OK;
}

/**
 * Add a datafeed callback to a session.
 *
 * @param session The session to use. Must not be NULL.
 * @param cb Function to call when a chunk of data is received.
 *           Must not be NULL.
 * @param cb_data Opaque pointer passed in by the caller.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_BUG No session exists.
 *
 * @since 0.3.0
 */
SR_API int sr_session_datafeed_callback_add(struct sr_session *session,
                sr_datafeed_callback cb, void *cb_data)
{
        struct datafeed_callback *cb_struct;

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_BUG;
        }

        if (!cb) {
                sr_err("%s: cb was NULL", __func__);
                return SR_ERR_ARG;
        }

        cb_struct = g_malloc0(sizeof(struct datafeed_callback));
        cb_struct->cb = cb;
        cb_struct->cb_data = cb_data;

        session->datafeed_callbacks =
            g_slist_append(session->datafeed_callbacks, cb_struct);

        return SR_OK;
}

/**
 * Get the trigger assigned to this session.
 *
 * @param session The session to use.
 *
 * @retval NULL Invalid (NULL) session was passed to the function.
 * @retval other The trigger assigned to this session (can be NULL).
 *
 * @since 0.4.0
 */
SR_API struct sr_trigger *sr_session_trigger_get(struct sr_session *session)
{
        if (!session)
                return NULL;

        return session->trigger;
}

/**
 * Set the trigger of this session.
 *
 * @param session The session to use. Must not be NULL.
 * @param trig The trigger to assign to this session. Can be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.4.0
 */
SR_API int sr_session_trigger_set(struct sr_session *session, struct sr_trigger *trig)
{
        if (!session)
                return SR_ERR_ARG;

        session->trigger = trig;

        return SR_OK;
}

static int verify_trigger(struct sr_trigger *trigger)
{
        struct sr_trigger_stage *stage;
        struct sr_trigger_match *match;
        GSList *l, *m;

        if (!trigger->stages) {
                sr_err("No trigger stages defined.");
                return SR_ERR;
        }

        sr_spew("Checking trigger:");
        for (l = trigger->stages; l; l = l->next) {
                stage = l->data;
                if (!stage->matches) {
                        sr_err("Stage %d has no matches defined.", stage->stage);
                        return SR_ERR;
                }
                for (m = stage->matches; m; m = m->next) {
                        match = m->data;
                        if (!match->channel) {
                                sr_err("Stage %d match has no channel.", stage->stage);
                                return SR_ERR;
                        }
                        if (!match->match) {
                                sr_err("Stage %d match is not defined.", stage->stage);
                                return SR_ERR;
                        }
                        sr_spew("Stage %d match on channel %s, match %d", stage->stage,
                                        match->channel->name, match->match);
                }
        }

        return SR_OK;
}

/** Set up the main context the session will be executing in.
 *
 * Must be called just before the session starts, by the thread which
 * will execute the session main loop. Once acquired, the main context
 * pointer is immutable for the duration of the session run.
 */
static int set_main_context(struct sr_session *session)
{
        GMainContext *main_context;

        g_mutex_lock(&session->main_mutex);

        /* May happen if sr_session_start() is called a second time
         * while the session is still running.
         */
        if (session->main_context) {
                sr_err("Main context already set.");

                g_mutex_unlock(&session->main_mutex);
                return SR_ERR;
        }
        main_context = g_main_context_ref_thread_default();
        /*
         * Try to use an existing main context if possible, but only if we
         * can make it owned by the current thread. Otherwise, create our
         * own main context so that event source callbacks can execute in
         * the session thread.
         */
        if (g_main_context_acquire(main_context)) {
                g_main_context_release(main_context);

                sr_dbg("Using thread-default main context.");
        } else {
                g_main_context_unref(main_context);

                sr_dbg("Creating our own main context.");
                main_context = g_main_context_new();
        }
        session->main_context = main_context;

        g_mutex_unlock(&session->main_mutex);

        return SR_OK;
}

/** Unset the main context used for the current session run.
 *
 * Must be called right after stopping the session. Note that if the
 * session is stopped asynchronously, the main loop may still be running
 * after the main context has been unset. This is OK as long as no new
 * event sources are created -- the main loop holds its own reference
 * to the main context.
 */
static int unset_main_context(struct sr_session *session)
{
        int ret;

        g_mutex_lock(&session->main_mutex);

        if (session->main_context) {
                g_main_context_unref(session->main_context);
                session->main_context = NULL;
                ret = SR_OK;
        } else {
                /* May happen if the set/unset calls are not matched.
                 */
                sr_err("No main context to unset.");
                ret = SR_ERR;
        }
        g_mutex_unlock(&session->main_mutex);

        return ret;
}

static unsigned int session_source_attach(struct sr_session *session,
                GSource *source)
{
        unsigned int id = 0;

        g_mutex_lock(&session->main_mutex);

        if (session->main_context)
                id = g_source_attach(source, session->main_context);
        else
                sr_err("Cannot add event source without main context.");

        g_mutex_unlock(&session->main_mutex);

        return id;
}

/* Idle handler; invoked when the number of registered event sources
 * for a running session drops to zero.
 */
static gboolean delayed_stop_check(void *data)
{
        struct sr_session *session;

        session = data;
        session->stop_check_id = 0;

        /* Session already ended? */
        if (!session->running)
                return G_SOURCE_REMOVE;

        /* New event sources may have been installed in the meantime. */
        if (g_hash_table_size(session->event_sources) != 0)
                return G_SOURCE_REMOVE;

        session->running = FALSE;
        unset_main_context(session);

        sr_info("Stopped.");

        /* This indicates a bug in user code, since it is not valid to
         * restart or destroy a session while it may still be running.
         */
        if (!session->main_loop && !session->stopped_callback) {
                sr_err("BUG: Session stop left unhandled.");
                return G_SOURCE_REMOVE;
        }
        if (session->main_loop)
                g_main_loop_quit(session->main_loop);

        if (session->stopped_callback)
                (*session->stopped_callback)(session->stopped_cb_data);

        return G_SOURCE_REMOVE;
}

static int stop_check_later(struct sr_session *session)
{
        GSource *source;
        unsigned int source_id;

        if (session->stop_check_id != 0)
                return SR_OK; /* idle handler already installed */

        source = g_idle_source_new();
        g_source_set_callback(source, &delayed_stop_check, session, NULL);

        source_id = session_source_attach(session, source);
        session->stop_check_id = source_id;

        g_source_unref(source);

        return (source_id != 0) ? SR_OK : SR_ERR;
}

/**
 * Start a session.
 *
 * When this function returns with a status code indicating success, the
 * session is running. Use sr_session_stopped_callback_set() to receive
 * notification upon completion, or call sr_session_run() to block until
 * the session stops.
 *
 * Session events will be processed in the context of the current thread.
 * If a thread-default GLib main context has been set, and is not owned by
 * any other thread, it will be used. Otherwise, libsigrok will create its
 * own main context for the current thread.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 * @retval SR_ERR Other error.
 *
 * @since 0.4.0
 */
SR_API int sr_session_start(struct sr_session *session)
{
        struct sr_dev_inst *sdi;
        struct sr_channel *ch;
        GSList *l, *c, *lend;
        int ret;

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        if (!session->devs) {
                sr_err("%s: session->devs was NULL; a session "
                       "cannot be started without devices.", __func__);
                return SR_ERR_ARG;
        }

        if (session->running) {
                sr_err("Cannot (re-)start session while it is still running.");
                return SR_ERR;
        }

        if (session->trigger) {
                ret = verify_trigger(session->trigger);
                if (ret != SR_OK)
                        return ret;
        }

        /* Check enabled channels and commit settings of all devices. */
        for (l = session->devs; l; l = l->next) {
                sdi = l->data;
                for (c = sdi->channels; c; c = c->next) {
                        ch = c->data;
                        if (ch->enabled)
                                break;
                }
                if (!c) {
                        sr_err("%s device %s has no enabled channels.",
                                sdi->driver->name, sdi->connection_id);
                        return SR_ERR;
                }

                ret = sr_config_commit(sdi);
                if (ret != SR_OK) {
                        sr_err("Failed to commit %s device %s settings "
                                "before starting acquisition.",
                                sdi->driver->name, sdi->connection_id);
                        return ret;
                }
        }

        ret = set_main_context(session);
        if (ret != SR_OK)
                return ret;

        sr_info("Starting.");

        session->running = TRUE;

        /* Have all devices start acquisition. */
        for (l = session->devs; l; l = l->next) {
                sdi = l->data;
                ret = sdi->driver->dev_acquisition_start(sdi, sdi);
                if (ret != SR_OK) {
                        sr_err("Could not start %s device %s acquisition.",
                                sdi->driver->name, sdi->connection_id);
                        break;
                }
        }

        if (ret != SR_OK) {
                /* If there are multiple devices, some of them may already have
                 * started successfully. Stop them now before returning. */
                lend = l->next;
                for (l = session->devs; l != lend; l = l->next) {
                        sdi = l->data;
                        if (sdi->driver->dev_acquisition_stop)
                                sdi->driver->dev_acquisition_stop(sdi, sdi);
                }
                /* TODO: Handle delayed stops. Need to iterate the event
                 * sources... */
                session->running = FALSE;

                unset_main_context(session);
                return ret;
        }

        if (g_hash_table_size(session->event_sources) == 0)
                stop_check_later(session);

        return SR_OK;
}

/**
 * Block until the running session stops.
 *
 * This is a convenience function which creates a GLib main loop and runs
 * it to process session events until the session stops.
 *
 * Instead of using this function, applications may run their own GLib main
 * loop, and use sr_session_stopped_callback_set() to receive notification
 * when the session finished running.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 * @retval SR_ERR Other error.
 *
 * @since 0.4.0
 */
SR_API int sr_session_run(struct sr_session *session)
{
        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }
        if (!session->running) {
                sr_err("No session running.");
                return SR_ERR;
        }
        if (session->main_loop) {
                sr_err("Main loop already created.");
                return SR_ERR;
        }

        g_mutex_lock(&session->main_mutex);

        if (!session->main_context) {
                sr_err("Cannot run without main context.");
                g_mutex_unlock(&session->main_mutex);
                return SR_ERR;
        }
        session->main_loop = g_main_loop_new(session->main_context, FALSE);

        g_mutex_unlock(&session->main_mutex);

        g_main_loop_run(session->main_loop);

        g_main_loop_unref(session->main_loop);
        session->main_loop = NULL;

        return SR_OK;
}

static gboolean session_stop_sync(void *user_data)
{
        struct sr_session *session;
        struct sr_dev_inst *sdi;
        GSList *node;

        session = user_data;

        if (!session->running)
                return G_SOURCE_REMOVE;

        sr_info("Stopping.");

        for (node = session->devs; node; node = node->next) {
                sdi = node->data;
                if (sdi->driver && sdi->driver->dev_acquisition_stop)
                        sdi->driver->dev_acquisition_stop(sdi, sdi);
        }

        return G_SOURCE_REMOVE;
}

/**
 * Stop a session.
 *
 * This requests the drivers of each device participating in the session to
 * abort the acquisition as soon as possible. Even after this function returns,
 * event processing still continues until all devices have actually stopped.
 *
 * Use sr_session_stopped_callback_set() to receive notification when the event
 * processing finished.
 *
 * This function is reentrant. That is, it may be called from a different
 * thread than the one executing the session, as long as it can be ensured
 * that the session object is valid.
 *
 * If the session is not running, sr_session_stop() silently does nothing.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_stop(struct sr_session *session)
{
        GMainContext *main_context;

        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }

        g_mutex_lock(&session->main_mutex);

        main_context = (session->main_context)
                ? g_main_context_ref(session->main_context)
                : NULL;

        g_mutex_unlock(&session->main_mutex);

        if (!main_context) {
                sr_dbg("No main context set; already stopped?");
                /* Not an error; as it would be racy. */
                return SR_OK;
        }
        g_main_context_invoke(main_context, &session_stop_sync, session);
        g_main_context_unref(main_context);

        return SR_OK;
}

/**
 * Return whether the session is currently running.
 *
 * Note that this function should be called from the same thread
 * the session was started in.
 *
 * @param session The session to use. Must not be NULL.
 *
 * @retval TRUE Session is running.
 * @retval FALSE Session is not running.
 * @retval SR_ERR_ARG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_is_running(struct sr_session *session)
{
        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }
        return session->running;
}

/**
 * Set the callback to be invoked after a session stopped running.
 *
 * Install a callback to receive notification when a session run stopped.
 * This can be used to integrate session execution with an existing main
 * loop, without having to block in sr_session_run().
 *
 * Note that the callback will be invoked in the context of the thread
 * that calls sr_session_start().
 *
 * @param session The session to use. Must not be NULL.
 * @param cb The callback to invoke on session stop. May be NULL to unset.
 * @param cb_data User data pointer to be passed to the callback.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid session passed.
 *
 * @since 0.4.0
 */
SR_API int sr_session_stopped_callback_set(struct sr_session *session,
                sr_session_stopped_callback cb, void *cb_data)
{
        if (!session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_ARG;
        }
        session->stopped_callback = cb;
        session->stopped_cb_data = cb_data;

        return SR_OK;
}

/**
 * Debug helper.
 *
 * @param packet The packet to show debugging information for.
 */
static void datafeed_dump(const struct sr_datafeed_packet *packet)
{
        const struct sr_datafeed_logic *logic;
        const struct sr_datafeed_analog_old *analog_old;
        const struct sr_datafeed_analog *analog;

        /* Please use the same order as in libsigrok.h. */
        switch (packet->type) {
        case SR_DF_HEADER:
                sr_dbg("bus: Received SR_DF_HEADER packet.");
                break;
        case SR_DF_END:
                sr_dbg("bus: Received SR_DF_END packet.");
                break;
        case SR_DF_META:
                sr_dbg("bus: Received SR_DF_META packet.");
                break;
        case SR_DF_TRIGGER:
                sr_dbg("bus: Received SR_DF_TRIGGER packet.");
                break;
        case SR_DF_LOGIC:
                logic = packet->payload;
                sr_dbg("bus: Received SR_DF_LOGIC packet (%" PRIu64 " bytes, "
                       "unitsize = %d).", logic->length, logic->unitsize);
                break;
        case SR_DF_ANALOG_OLD:
                analog_old = packet->payload;
                sr_dbg("bus: Received SR_DF_ANALOG_OLD packet (%d samples).",
                       analog_old->num_samples);
                break;
        case SR_DF_FRAME_BEGIN:
                sr_dbg("bus: Received SR_DF_FRAME_BEGIN packet.");
                break;
        case SR_DF_FRAME_END:
                sr_dbg("bus: Received SR_DF_FRAME_END packet.");
                break;
        case SR_DF_ANALOG:
                analog = packet->payload;
                sr_dbg("bus: Received SR_DF_ANALOG packet (%d samples).",
                       analog->num_samples);
                break;
        default:
                sr_dbg("bus: Received unknown packet type: %d.", packet->type);
                break;
        }
}

/**
 * Send a packet to whatever is listening on the datafeed bus.
 *
 * Hardware drivers use this to send a data packet to the frontend.
 *
 * @param sdi TODO.
 * @param packet The datafeed packet to send to the session bus.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @private
 */
SR_PRIV int sr_session_send(const struct sr_dev_inst *sdi,
                const struct sr_datafeed_packet *packet)
{
        GSList *l;
        struct datafeed_callback *cb_struct;
        struct sr_datafeed_packet *packet_in, *packet_out;
        struct sr_transform *t;
        int ret;

        if (!sdi) {
                sr_err("%s: sdi was NULL", __func__);
                return SR_ERR_ARG;
        }

        if (!packet) {
                sr_err("%s: packet was NULL", __func__);
                return SR_ERR_ARG;
        }

        if (!sdi->session) {
                sr_err("%s: session was NULL", __func__);
                return SR_ERR_BUG;
        }

        if (packet->type == SR_DF_ANALOG_OLD) {
                /* Convert to SR_DF_ANALOG. */
                const struct sr_datafeed_analog_old *analog_old = packet->payload;
                struct sr_analog_encoding encoding;
                struct sr_analog_meaning meaning;
                struct sr_analog_spec spec;
                struct sr_datafeed_analog analog;
                struct sr_datafeed_packet new_packet;
                new_packet.type = SR_DF_ANALOG;
                new_packet.payload = &analog;
                analog.data = analog_old->data;
                analog.num_samples = analog_old->num_samples;
                analog.encoding = &encoding;
                analog.meaning = &meaning;
                analog.spec = &spec;
                encoding.unitsize = sizeof(float);
                encoding.is_signed = TRUE;
                encoding.is_float = TRUE;
#ifdef WORDS_BIGENDIAN
                encoding.is_bigendian = TRUE;
#else
                encoding.is_bigendian = FALSE;
#endif
                encoding.digits = 0;
                encoding.is_digits_decimal = FALSE;
                encoding.scale.p = 1;
                encoding.scale.q = 1;
                encoding.offset.p = 0;
                encoding.offset.q = 1;
                meaning.mq = analog_old->mq;
                meaning.unit = analog_old->unit;
                meaning.mqflags = analog_old->mqflags;
                meaning.channels = analog_old->channels;
                spec.spec_digits = 0;
                return sr_session_send(sdi, &new_packet);
        }

        /*
         * Pass the packet to the first transform module. If that returns
         * another packet (instead of NULL), pass that packet to the next
         * transform module in the list, and so on.
         */
        packet_in = (struct sr_datafeed_packet *)packet;
        for (l = sdi->session->transforms; l; l = l->next) {
                t = l->data;
                sr_spew("Running transform module '%s'.", t->module->id);
                ret = t->module->receive(t, packet_in, &packet_out);
                if (ret < 0) {
                        sr_err("Error while running transform module: %d.", ret);
                        return SR_ERR;
                }
                if (!packet_out) {
                        /*
                         * If any of the transforms don't return an output
                         * packet, abort.
                         */
                        sr_spew("Transform module didn't return a packet, aborting.");
                        return SR_OK;
                } else {
                        /*
                         * Use this transform module's output packet as input
                         * for the next transform module.
                         */
                        packet_in = packet_out;
                }
        }
        packet = packet_in;

        /*
         * If the last transform did output a packet, pass it to all datafeed
         * callbacks.
         */
        for (l = sdi->session->datafeed_callbacks; l; l = l->next) {
                if (sr_log_loglevel_get() >= SR_LOG_DBG)
                        datafeed_dump(packet);
                cb_struct = l->data;
                cb_struct->cb(sdi, packet, cb_struct->cb_data);
        }

        return SR_OK;
}

/**
 * Add an event source for a file descriptor.
 *
 * @param session The session to use. Must not be NULL.
 * @param key The key which identifies the event source.
 * @param source An event source object. Must not be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 * @retval SR_ERR_BUG Event source with @a key already installed.
 * @retval SR_ERR Other error.
 *
 * @private
 */
SR_PRIV int sr_session_source_add_internal(struct sr_session *session,
                void *key, GSource *source)
{
        /*
         * This must not ever happen, since the source has already been
         * created and its finalize() method will remove the key for the
         * already installed source. (Well it would, if we did not have
         * another sanity check there.)
         */
        if (g_hash_table_contains(session->event_sources, key)) {
                sr_err("Event source with key %p already exists.", key);
                return SR_ERR_BUG;
        }
        g_hash_table_insert(session->event_sources, key, source);

        if (session_source_attach(session, source) == 0)
                return SR_ERR;

        return SR_OK;
}

SR_PRIV int sr_session_fd_source_add(struct sr_session *session,
                void *key, gintptr fd, int events, int timeout,
                sr_receive_data_callback cb, void *cb_data)
{
        GSource *source;
        int ret;

        source = fd_source_new(session, key, fd, events, timeout);
        if (!source)
                return SR_ERR;

        g_source_set_callback(source, (GSourceFunc)cb, cb_data, NULL);

        ret = sr_session_source_add_internal(session, key, source);
        g_source_unref(source);

        return ret;
}

/**
 * Add an event source for a file descriptor.
 *
 * @param session The session to use. Must not be NULL.
 * @param fd The file descriptor, or a negative value to create a timer source.
 * @param events Events to check for.
 * @param timeout Max time in ms to wait before the callback is called,
 *                or -1 to wait indefinitely.
 * @param cb Callback function to add. Must not be NULL.
 * @param cb_data Data for the callback function. Can be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.3.0
 * @private
 */
SR_PRIV int sr_session_source_add(struct sr_session *session, int fd,
                int events, int timeout, sr_receive_data_callback cb, void *cb_data)
{
        if (fd < 0 && timeout < 0) {
                sr_err("Cannot create timer source without timeout.");
                return SR_ERR_ARG;
        }
        return sr_session_fd_source_add(session, GINT_TO_POINTER(fd),
                        fd, events, timeout, cb, cb_data);
}

/**
 * Add an event source for a GPollFD.
 *
 * @param session The session to use. Must not be NULL.
 * @param pollfd The GPollFD. Must not be NULL.
 * @param timeout Max time in ms to wait before the callback is called,
 *                or -1 to wait indefinitely.
 * @param cb Callback function to add. Must not be NULL.
 * @param cb_data Data for the callback function. Can be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.3.0
 * @private
 */
SR_PRIV int sr_session_source_add_pollfd(struct sr_session *session,
                GPollFD *pollfd, int timeout, sr_receive_data_callback cb,
                void *cb_data)
{
        if (!pollfd) {
                sr_err("%s: pollfd was NULL", __func__);
                return SR_ERR_ARG;
        }
        return sr_session_fd_source_add(session, pollfd, pollfd->fd,
                        pollfd->events, timeout, cb, cb_data);
}

/**
 * Add an event source for a GIOChannel.
 *
 * @param session The session to use. Must not be NULL.
 * @param channel The GIOChannel.
 * @param events Events to poll on.
 * @param timeout Max time in ms to wait before the callback is called,
 *                or -1 to wait indefinitely.
 * @param cb Callback function to add. Must not be NULL.
 * @param cb_data Data for the callback function. Can be NULL.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 *
 * @since 0.3.0
 * @private
 */
SR_PRIV int sr_session_source_add_channel(struct sr_session *session,
                GIOChannel *channel, int events, int timeout,
                sr_receive_data_callback cb, void *cb_data)
{
        GPollFD pollfd;

        if (!channel) {
                sr_err("%s: channel was NULL", __func__);
                return SR_ERR_ARG;
        }
        /* We should be using g_io_create_watch(), but can't without
         * changing the driver API, as the callback signature is different.
         */
#ifdef G_OS_WIN32
        g_io_channel_win32_make_pollfd(channel, events, &pollfd);
#else
        pollfd.fd = g_io_channel_unix_get_fd(channel);
        pollfd.events = events;
#endif
        return sr_session_fd_source_add(session, channel, pollfd.fd,
                        pollfd.events, timeout, cb, cb_data);
}

/**
 * Remove the source identified by the specified poll object.
 *
 * @param session The session to use. Must not be NULL.
 * @param key The key by which the source is identified.
 *
 * @retval SR_OK Success
 * @retval SR_ERR_BUG No event source for poll_object found.
 *
 * @private
 */
SR_PRIV int sr_session_source_remove_internal(struct sr_session *session,
                void *key)
{
        GSource *source;

        source = g_hash_table_lookup(session->event_sources, key);
        /*
         * Trying to remove an already removed event source is problematic
         * since the poll_object handle may have been reused in the meantime.
         */
        if (!source) {
                sr_warn("Cannot remove non-existing event source %p.", key);
                return SR_ERR_BUG;
        }
        g_source_destroy(source);

        return SR_OK;
}

/**
 * Remove the source belonging to the specified file descriptor.
 *
 * @param session The session to use. Must not be NULL.
 * @param fd The file descriptor for which the source should be removed.
 *
 * @retval SR_OK Success
 * @retval SR_ERR_ARG Invalid argument
 * @retval SR_ERR_BUG Internal error.
 *
 * @since 0.3.0
 * @private
 */
SR_PRIV int sr_session_source_remove(struct sr_session *session, int fd)
{
        return sr_session_source_remove_internal(session, GINT_TO_POINTER(fd));
}

/**
 * Remove the source belonging to the specified poll descriptor.
 *
 * @param session The session to use. Must not be NULL.
 * @param pollfd The poll descriptor for which the source should be removed.
 *               Must not be NULL.
 * @return SR_OK upon success, SR_ERR_ARG upon invalid arguments, or
 *         SR_ERR_MALLOC upon memory allocation errors, SR_ERR_BUG upon
 *         internal errors.
 *
 * @since 0.2.0
 * @private
 */
SR_PRIV int sr_session_source_remove_pollfd(struct sr_session *session,
                GPollFD *pollfd)
{
        if (!pollfd) {
                sr_err("%s: pollfd was NULL", __func__);
                return SR_ERR_ARG;
        }
        return sr_session_source_remove_internal(session, pollfd);
}

/**
 * Remove the source belonging to the specified channel.
 *
 * @param session The session to use. Must not be NULL.
 * @param channel The channel for which the source should be removed.
 *                Must not be NULL.
 * @retval SR_OK Success.
 * @retval SR_ERR_ARG Invalid argument.
 * @return SR_ERR_BUG Internal error.
 *
 * @since 0.2.0
 * @private
 */
SR_PRIV int sr_session_source_remove_channel(struct sr_session *session,
                GIOChannel *channel)
{
        if (!channel) {
                sr_err("%s: channel was NULL", __func__);
                return SR_ERR_ARG;
        }
        return sr_session_source_remove_internal(session, channel);
}

/** Unregister an event source that has been destroyed.
 *
 * This is intended to be called from a source's finalize() method.
 *
 * @param session The session to use. Must not be NULL.
 * @param key The key used to identify @a source.
 * @param source The source object that was destroyed.
 *
 * @retval SR_OK Success.
 * @retval SR_ERR_BUG Event source for @a key does not match @a source.
 * @retval SR_ERR Other error.
 *
 * @private
 */
SR_PRIV int sr_session_source_destroyed(struct sr_session *session,
                void *key, GSource *source)
{
        GSource *registered_source;

        registered_source = g_hash_table_lookup(session->event_sources, key);
        /*
         * Trying to remove an already removed event source is problematic
         * since the poll_object handle may have been reused in the meantime.
         */
        if (!registered_source) {
                sr_err("No event source for key %p found.", key);
                return SR_ERR_BUG;
        }
        if (registered_source != source) {
                sr_err("Event source for key %p does not match"
                        " destroyed source.", key);
                return SR_ERR_BUG;
        }
        g_hash_table_remove(session->event_sources, key);

        if (g_hash_table_size(session->event_sources) > 0)
                return SR_OK;

        /* If no event sources are left, consider the acquisition finished.
         * This is pretty crude, as it requires all event sources to be
         * registered via the libsigrok API.
         */
        return stop_check_later(session);
}

static void copy_src(struct sr_config *src, struct sr_datafeed_meta *meta_copy)
{
        g_variant_ref(src->data);
        meta_copy->config = g_slist_append(meta_copy->config,
                                           g_memdup(src, sizeof(struct sr_config)));
}

SR_PRIV int sr_packet_copy(const struct sr_datafeed_packet *packet,
                struct sr_datafeed_packet **copy)
{
        const struct sr_datafeed_meta *meta;
        struct sr_datafeed_meta *meta_copy;
        const struct sr_datafeed_logic *logic;
        struct sr_datafeed_logic *logic_copy;
        const struct sr_datafeed_analog_old *analog_old;
        struct sr_datafeed_analog_old *analog_old_copy;
        const struct sr_datafeed_analog *analog;
        struct sr_datafeed_analog *analog_copy;
        uint8_t *payload;

        *copy = g_malloc0(sizeof(struct sr_datafeed_packet));
        (*copy)->type = packet->type;

        switch (packet->type) {
        case SR_DF_TRIGGER:
        case SR_DF_END:
                /* No payload. */
                break;
        case SR_DF_HEADER:
                payload = g_malloc(sizeof(struct sr_datafeed_header));
                memcpy(payload, packet->payload, sizeof(struct sr_datafeed_header));
                (*copy)->payload = payload;
                break;
        case SR_DF_META:
                meta = packet->payload;
                meta_copy = g_malloc0(sizeof(struct sr_datafeed_meta));
                g_slist_foreach(meta->config, (GFunc)copy_src, meta_copy->config);
                (*copy)->payload = meta_copy;
                break;
        case SR_DF_LOGIC:
                logic = packet->payload;
                logic_copy = g_malloc(sizeof(logic));
                logic_copy->length = logic->length;
                logic_copy->unitsize = logic->unitsize;
                memcpy(logic_copy->data, logic->data, logic->length * logic->unitsize);
                (*copy)->payload = logic_copy;
                break;
        case SR_DF_ANALOG_OLD:
                analog_old = packet->payload;
                analog_old_copy = g_malloc(sizeof(analog_old));
                analog_old_copy->channels = g_slist_copy(analog_old->channels);
                analog_old_copy->num_samples = analog_old->num_samples;
                analog_old_copy->mq = analog_old->mq;
                analog_old_copy->unit = analog_old->unit;
                analog_old_copy->mqflags = analog_old->mqflags;
                analog_old_copy->data = g_malloc(analog_old->num_samples * sizeof(float));
                memcpy(analog_old_copy->data, analog_old->data,
                                analog_old->num_samples * sizeof(float));
                (*copy)->payload = analog_old_copy;
                break;
        case SR_DF_ANALOG:
                analog = packet->payload;
                analog_copy = g_malloc(sizeof(analog));
                analog_copy->data = g_malloc(
                                analog->encoding->unitsize * analog->num_samples);
                memcpy(analog_copy->data, analog->data,
                                analog->encoding->unitsize * analog->num_samples);
                analog_copy->num_samples = analog->num_samples;
                analog_copy->encoding = g_memdup(analog->encoding,
                                sizeof(struct sr_analog_encoding));
                analog_copy->meaning = g_memdup(analog->meaning,
                                sizeof(struct sr_analog_meaning));
                analog_copy->meaning->channels = g_slist_copy(
                                analog->meaning->channels);
                analog_copy->spec = g_memdup(analog->spec,
                                sizeof(struct sr_analog_spec));
                (*copy)->payload = analog_copy;
                break;
        default:
                sr_err("Unknown packet type %d", packet->type);
                return SR_ERR;
        }

        return SR_OK;
}

void sr_packet_free(struct sr_datafeed_packet *packet)
{
        const struct sr_datafeed_meta *meta;
        const struct sr_datafeed_logic *logic;
        const struct sr_datafeed_analog_old *analog_old;
        const struct sr_datafeed_analog *analog;
        struct sr_config *src;
        GSList *l;

        switch (packet->type) {
        case SR_DF_TRIGGER:
        case SR_DF_END:
                /* No payload. */
                break;
        case SR_DF_HEADER:
                /* Payload is a simple struct. */
                g_free((void *)packet->payload);
                break;
        case SR_DF_META:
                meta = packet->payload;
                for (l = meta->config; l; l = l->next) {
                        src = l->data;
                        g_variant_unref(src->data);
                        g_free(src);
                }
                g_slist_free(meta->config);
                g_free((void *)packet->payload);
                break;
        case SR_DF_LOGIC:
                logic = packet->payload;
                g_free(logic->data);
                g_free((void *)packet->payload);
                break;
        case SR_DF_ANALOG_OLD:
                analog_old = packet->payload;
                g_slist_free(analog_old->channels);
                g_free(analog_old->data);
                g_free((void *)packet->payload);
                break;
        case SR_DF_ANALOG:
                analog = packet->payload;
                g_free(analog->data);
                g_free(analog->encoding);
                g_slist_free(analog->meaning->channels);
                g_free(analog->meaning);
                g_free(analog->spec);
                g_free((void *)packet->payload);
                break;
        default:
                sr_err("Unknown packet type %d", packet->type);
        }
        g_free(packet);

}

/** @} */