util: add helper APIs for dealing with inotify in portable manner

The inotify userspace API for reading events is quite horrible, so it is
useful to wrap it in a more friendly API to avoid duplicating code
across many users in QEMU. Wrapping it also allows introduction of a
platform portability layer, so that we can add impls for non-Linux based
equivalents in future.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

9 files changed, 1234 insertions, 1 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 738580884f..e4c611291b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2087,6 +2087,13 @@ F: include/qemu/sockets.h
 F: util/qemu-sockets.c
 F: qapi/sockets.json
 
+File monitor
+M: Daniel P. Berrange <berrange@redhat.com>
+S: Odd fixes
+F: util/filemonitor*.c
+F: include/qemu/filemonitor.h
+F: tests/test-util-filemonitor.c
+
 Throttling infrastructure
 M: Alberto Garcia <berto@igalia.com>
 S: Supported
diff --git a/Makefile.objs b/Makefile.objs
index 5fb022d7ad..0897a346db 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -1,6 +1,6 @@
 #######################################################################
 # Common libraries for tools and emulators
-stub-obj-y = stubs/ crypto/
+stub-obj-y = stubs/ util/ crypto/
 util-obj-y = util/ qobject/ qapi/
 
 chardev-obj-y = chardev/
diff --git a/include/qemu/filemonitor.h b/include/qemu/filemonitor.h
new file mode 100644
index 0000000000..cd031832ed
--- /dev/null
+++ b/include/qemu/filemonitor.h
@@ -0,0 +1,128 @@
+/*
+ * QEMU file monitor helper
+ *
+ * Copyright (c) 2018 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/>.
+ *
+ */
+
+#ifndef QEMU_FILE_MONITOR_H
+#define QEMU_FILE_MONITOR_H
+
+#include "qemu-common.h"
+
+
+typedef struct QFileMonitor QFileMonitor;
+
+typedef enum {
+    /* File has been created in a dir */
+    QFILE_MONITOR_EVENT_CREATED,
+    /* File has been modified in a dir */
+    QFILE_MONITOR_EVENT_MODIFIED,
+    /* File has been deleted in a dir */
+    QFILE_MONITOR_EVENT_DELETED,
+    /* File has attributes changed */
+    QFILE_MONITOR_EVENT_ATTRIBUTES,
+    /* Dir is no longer being monitored (due to deletion) */
+    QFILE_MONITOR_EVENT_IGNORED,
+} QFileMonitorEvent;
+
+
+/**
+ * QFileMonitorHandler:
+ * @id: id from qemu_file_monitor_add_watch()
+ * @event: the file change that occurred
+ * @filename: the name of the file affected
+ * @opaque: opaque data provided to qemu_file_monitor_add_watch()
+ *
+ * Invoked whenever a file changes. If @event is
+ * QFILE_MONITOR_EVENT_IGNORED, @filename will be
+ * empty.
+ *
+ */
+typedef void (*QFileMonitorHandler)(int id,
+                                    QFileMonitorEvent event,
+                                    const char *filename,
+                                    void *opaque);
+
+/**
+ * qemu_file_monitor_new:
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Create a handle for a file monitoring object.
+ *
+ * This object does locking internally to enable it to be
+ * safe to use from multiple threads
+ *
+ * If the platform does not support file monitoring, an
+ * error will be reported. Likewise if file monitoring
+ * is supported, but cannot be initialized
+ *
+ * Currently this is implemented on Linux platforms with
+ * the inotify subsystem.
+ *
+ * Returns: the new monitoring object, or NULL on error
+ */
+QFileMonitor *qemu_file_monitor_new(Error **errp);
+
+/**
+ * qemu_file_monitor_free:
+ * @mon: the file monitor context
+ *
+ * Free resources associated with the file monitor,
+ * including any currently registered watches.
+ */
+void qemu_file_monitor_free(QFileMonitor *mon);
+
+/**
+ * qemu_file_monitor_add_watch:
+ * @mon: the file monitor context
+ * @dirpath: the directory whose contents to watch
+ * @filename: optional filename to filter on
+ * @cb: the function to invoke when @dirpath has changes
+ * @opaque: data to pass to @cb
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Register to receive notifications of changes
+ * in the directory @dirpath. All files in the
+ * directory will be monitored. If the caller is
+ * only interested in one specific file, @filename
+ * can be used to filter events.
+ *
+ * Returns: a positive integer watch ID, or -1 on error
+ */
+int qemu_file_monitor_add_watch(QFileMonitor *mon,
+                                const char *dirpath,
+                                const char *filename,
+                                QFileMonitorHandler cb,
+                                void *opaque,
+                                Error **errp);
+
+/**
+ * qemu_file_monitor_remove_watch:
+ * @mon: the file monitor context
+ * @dirpath: the directory whose contents to unwatch
+ * @id: id of the watch to remove
+ *
+ * Removes the file monitoring watch @id, associated
+ * with the directory @dirpath. This must never be
+ * called from a QFileMonitorHandler callback, or a
+ * deadlock will result.
+ */
+void qemu_file_monitor_remove_watch(QFileMonitor *mon,
+                                    const char *dirpath,
+                                    int id);
+
+#endif /* QEMU_FILE_MONITOR_H */
diff --git a/tests/Makefile.include b/tests/Makefile.include
index 3741f8f6dd..f15f4e88bc 100644
--- a/tests/Makefile.include
+++ b/tests/Makefile.include
@@ -114,6 +114,7 @@ ifneq (,$(findstring qemu-ga,$(TOOLS)))
 check-unit-$(land,$(CONFIG_LINUX),$(CONFIG_VIRTIO_SERIAL)) += tests/test-qga$(EXESUF)
 endif
 check-unit-y += tests/test-timed-average$(EXESUF)
+check-unit-$(CONFIG_INOTIFY1) += tests/test-util-filemonitor$(EXESUF)
 check-unit-y += tests/test-util-sockets$(EXESUF)
 check-unit-y += tests/test-io-task$(EXESUF)
 check-unit-y += tests/test-io-channel-socket$(EXESUF)
@@ -657,6 +658,8 @@ tests/test-crypto-tlssession$(EXESUF): tests/test-crypto-tlssession.o \
 	tests/crypto-tls-x509-helpers.o tests/pkix_asn1_tab.o \
 	tests/crypto-tls-psk-helpers.o \
         $(test-crypto-obj-y)
+tests/test-util-filemonitor$(EXESUF): tests/test-util-filemonitor.o \
+	$(test-util-obj-y)
 tests/test-util-sockets$(EXESUF): tests/test-util-sockets.o \
 	tests/socket-helpers.o $(test-util-obj-y)
 tests/test-io-task$(EXESUF): tests/test-io-task.o $(test-io-obj-y)
diff --git a/tests/test-util-filemonitor.c b/tests/test-util-filemonitor.c
new file mode 100644
index 0000000000..5d95cea5ee
--- /dev/null
+++ b/tests/test-util-filemonitor.c
@@ -0,0 +1,685 @@
+/*
+ * Tests for util/filemonitor-*.c
+ *
+ * Copyright 2018 Red Hat, Inc.
+ *
+ * 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 2 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 library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/main-loop.h"
+#include "qapi/error.h"
+#include "qemu/filemonitor.h"
+
+#include <utime.h>
+
+enum {
+    QFILE_MONITOR_TEST_OP_CREATE,
+    QFILE_MONITOR_TEST_OP_APPEND,
+    QFILE_MONITOR_TEST_OP_TRUNC,
+    QFILE_MONITOR_TEST_OP_RENAME,
+    QFILE_MONITOR_TEST_OP_TOUCH,
+    QFILE_MONITOR_TEST_OP_UNLINK,
+};
+
+typedef struct {
+    int type;
+    const char *filesrc;
+    const char *filedst;
+} QFileMonitorTestOp;
+
+typedef struct {
+    const char *file;
+} QFileMonitorTestWatch;
+
+typedef struct {
+    gsize nwatches;
+    const QFileMonitorTestWatch *watches;
+
+    gsize nops;
+    const QFileMonitorTestOp *ops;
+} QFileMonitorTestPlan;
+
+typedef struct {
+    int id;
+    QFileMonitorEvent event;
+    char *filename;
+} QFileMonitorTestRecord;
+
+
+typedef struct {
+    QemuMutex lock;
+    GList *records;
+} QFileMonitorTestData;
+
+static QemuMutex evlock;
+static bool evstopping;
+static bool evrunning;
+
+/*
+ * Main function for a background thread that is
+ * running the event loop during the test
+ */
+static void *
+qemu_file_monitor_test_event_loop(void *opaque G_GNUC_UNUSED)
+{
+    qemu_mutex_lock(&evlock);
+
+    while (!evstopping) {
+        qemu_mutex_unlock(&evlock);
+        main_loop_wait(true);
+        qemu_mutex_lock(&evlock);
+    }
+
+    evrunning = false;
+    qemu_mutex_unlock(&evlock);
+    return NULL;
+}
+
+
+/*
+ * File monitor event handler which simply maintains
+ * an ordered list of all events that it receives
+ */
+static void
+qemu_file_monitor_test_handler(int id,
+                               QFileMonitorEvent event,
+                               const char *filename,
+                               void *opaque)
+{
+    QFileMonitorTestData *data = opaque;
+    QFileMonitorTestRecord *rec = g_new0(QFileMonitorTestRecord, 1);
+
+    rec->id = id;
+    rec->event = event;
+    rec->filename = g_strdup(filename);
+
+    qemu_mutex_lock(&data->lock);
+    data->records = g_list_append(data->records, rec);
+    qemu_mutex_unlock(&data->lock);
+}
+
+
+static void
+qemu_file_monitor_test_record_free(QFileMonitorTestRecord *rec)
+{
+    g_free(rec->filename);
+    g_free(rec);
+}
+
+
+/*
+ * Get the next event record that has been received by
+ * the file monitor event handler. Since events are
+ * emitted in the background thread running the event
+ * loop, we can't assume there is a record available
+ * immediately. Thus we will sleep for upto 5 seconds
+ * to wait for the event to be queued for us.
+ */
+static QFileMonitorTestRecord *
+qemu_file_monitor_test_next_record(QFileMonitorTestData *data)
+{
+    GTimer *timer = g_timer_new();
+    QFileMonitorTestRecord *record = NULL;
+    GList *tmp;
+
+    qemu_mutex_lock(&data->lock);
+    while (!data->records && g_timer_elapsed(timer, NULL) < 5) {
+        qemu_mutex_unlock(&data->lock);
+        usleep(10 * 1000);
+        qemu_mutex_lock(&data->lock);
+    }
+    if (data->records) {
+        record = data->records->data;
+        tmp = data->records;
+        data->records = g_list_remove_link(data->records, tmp);
+        g_list_free(tmp);
+    }
+    qemu_mutex_unlock(&data->lock);
+
+    g_timer_destroy(timer);
+    return record;
+}
+
+
+/*
+ * Check whether the event record we retrieved matches
+ * data we were expecting to see for the event
+ */
+static bool
+qemu_file_monitor_test_expect(QFileMonitorTestData *data,
+                              int id,
+                              QFileMonitorEvent event,
+                              const char *filename)
+{
+    QFileMonitorTestRecord *rec;
+    bool ret = false;
+
+    rec = qemu_file_monitor_test_next_record(data);
+
+    if (!rec) {
+        g_printerr("Missing event watch id %d event %d file %s\n",
+                   id, event, filename);
+        return false;
+    }
+
+    if (id != rec->id) {
+        g_printerr("Expected watch id %d but got %d\n", id, rec->id);
+        goto cleanup;
+    }
+
+    if (event != rec->event) {
+        g_printerr("Expected event %d but got %d\n", event, rec->event);
+        goto cleanup;
+    }
+
+    if (!g_str_equal(filename, rec->filename)) {
+        g_printerr("Expected filename %s but got %s\n",
+                   filename, rec->filename);
+        goto cleanup;
+    }
+
+    ret = true;
+
+ cleanup:
+    qemu_file_monitor_test_record_free(rec);
+    return ret;
+}
+
+
+static void
+test_file_monitor_events(const void *opaque)
+{
+    const QFileMonitorTestPlan *plan = opaque;
+    Error *local_err = NULL;
+    GError *gerr = NULL;
+    QFileMonitor *mon = qemu_file_monitor_new(&local_err);
+    QemuThread th;
+    GTimer *timer;
+    gchar *dir = NULL;
+    int err = -1;
+    gsize i, j;
+    char *pathsrc = NULL;
+    char *pathdst = NULL;
+    QFileMonitorTestData data;
+
+    qemu_mutex_init(&data.lock);
+    data.records = NULL;
+
+    /*
+     * The file monitor needs the main loop running in
+     * order to receive events from inotify. We must
+     * thus spawn a background thread to run an event
+     * loop impl, while this thread triggers the
+     * actual file operations we're testing
+     */
+    evrunning = 1;
+    evstopping = 0;
+    qemu_thread_create(&th, "event-loop",
+                       qemu_file_monitor_test_event_loop, NULL,
+                       QEMU_THREAD_JOINABLE);
+
+    if (local_err) {
+        g_printerr("File monitoring not available: %s",
+                   error_get_pretty(local_err));
+        error_free(local_err);
+        return;
+    }
+
+    dir = g_dir_make_tmp("test-util-filemonitor-XXXXXX",
+                         &gerr);
+    if (!dir) {
+        g_printerr("Unable to create tmp dir %s",
+                   gerr->message);
+        g_error_free(gerr);
+        abort();
+    }
+
+    /*
+     * First register all the directory / file watches
+     * we're interested in seeing events against
+     */
+    for (i = 0; i < plan->nwatches; i++) {
+        int watchid;
+        watchid = qemu_file_monitor_add_watch(mon,
+                                              dir,
+                                              plan->watches[i].file,
+                                              qemu_file_monitor_test_handler,
+                                              &data,
+                                              &local_err);
+        if (watchid < 0) {
+            g_printerr("Unable to add watch %s",
+                       error_get_pretty(local_err));
+            goto cleanup;
+        }
+    }
+
+
+    /*
+     * Now invoke all the file operations (create,
+     * delete, rename, chmod, etc). These operations
+     * will trigger the various file monitor events
+     */
+    for (i = 0; i < plan->nops; i++) {
+        const QFileMonitorTestOp *op = &(plan->ops[i]);
+        int fd;
+        struct utimbuf ubuf;
+
+        pathsrc = g_strdup_printf("%s/%s", dir, op->filesrc);
+        if (op->filedst) {
+            pathdst = g_strdup_printf("%s/%s", dir, op->filedst);
+        }
+
+        switch (op->type) {
+        case QFILE_MONITOR_TEST_OP_CREATE:
+            fd = open(pathsrc, O_WRONLY | O_CREAT, 0700);
+            if (fd < 0) {
+                g_printerr("Unable to create %s: %s",
+                           pathsrc, strerror(errno));
+                goto cleanup;
+            }
+            close(fd);
+            break;
+
+        case QFILE_MONITOR_TEST_OP_APPEND:
+            fd = open(pathsrc, O_WRONLY | O_APPEND, 0700);
+            if (fd < 0) {
+                g_printerr("Unable to open %s: %s",
+                           pathsrc, strerror(errno));
+                goto cleanup;
+            }
+
+            if (write(fd, "Hello World", 10) != 10) {
+                g_printerr("Unable to write %s: %s",
+                           pathsrc, strerror(errno));
+                close(fd);
+                goto cleanup;
+            }
+            close(fd);
+            break;
+
+        case QFILE_MONITOR_TEST_OP_TRUNC:
+            if (truncate(pathsrc, 4) < 0) {
+                g_printerr("Unable to truncate %s: %s",
+                           pathsrc, strerror(errno));
+                goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_RENAME:
+            if (rename(pathsrc, pathdst) < 0) {
+                g_printerr("Unable to rename %s to %s: %s",
+                           pathsrc, pathdst, strerror(errno));
+                goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_UNLINK:
+            if (unlink(pathsrc) < 0) {
+                g_printerr("Unable to unlink %s: %s",
+                           pathsrc, strerror(errno));
+                goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_TOUCH:
+            ubuf.actime = 1024;
+            ubuf.modtime = 1025;
+            if (utime(pathsrc, &ubuf) < 0) {
+                g_printerr("Unable to touch %s: %s",
+                           pathsrc, strerror(errno));
+                goto cleanup;
+            }
+            break;
+
+        default:
+            g_assert_not_reached();
+        }
+
+        g_free(pathsrc);
+        g_free(pathdst);
+        pathsrc = pathdst = NULL;
+    }
+
+
+    /*
+     * Finally validate that we have received all the events
+     * we expect to see for the combination of watches and
+     * file operations
+     */
+    for (i = 0; i < plan->nops; i++) {
+        const QFileMonitorTestOp *op = &(plan->ops[i]);
+
+        switch (op->type) {
+        case QFILE_MONITOR_TEST_OP_CREATE:
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filesrc))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_CREATED, op->filesrc))
+                    goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_APPEND:
+        case QFILE_MONITOR_TEST_OP_TRUNC:
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filesrc))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_MODIFIED, op->filesrc))
+                    goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_RENAME:
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filesrc))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_DELETED, op->filesrc))
+                    goto cleanup;
+            }
+
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filedst))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_CREATED, op->filedst))
+                    goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_TOUCH:
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filesrc))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_ATTRIBUTES, op->filesrc))
+                    goto cleanup;
+            }
+            break;
+
+        case QFILE_MONITOR_TEST_OP_UNLINK:
+            for (j = 0; j < plan->nwatches; j++) {
+                if (plan->watches[j].file &&
+                    !g_str_equal(plan->watches[j].file, op->filesrc))
+                    continue;
+
+                if (!qemu_file_monitor_test_expect(
+                        &data, j, QFILE_MONITOR_EVENT_DELETED, op->filesrc))
+                    goto cleanup;
+            }
+            break;
+
+        default:
+            g_assert_not_reached();
+        }
+    }
+
+    err = 0;
+
+ cleanup:
+    g_free(pathsrc);
+    g_free(pathdst);
+
+    qemu_mutex_lock(&evlock);
+    evstopping = 1;
+    timer = g_timer_new();
+    while (evrunning && g_timer_elapsed(timer, NULL) < 5) {
+        qemu_mutex_unlock(&evlock);
+        usleep(10 * 1000);
+        qemu_mutex_lock(&evlock);
+    }
+    qemu_mutex_unlock(&evlock);
+
+    if (g_timer_elapsed(timer, NULL) >= 5) {
+        g_printerr("Event loop failed to quit after 5 seconds\n");
+    }
+    g_timer_destroy(timer);
+
+    for (i = 0; i < plan->nops; i++) {
+        const QFileMonitorTestOp *op = &(plan->ops[i]);
+        pathsrc = g_strdup_printf("%s/%s", dir, op->filesrc);
+        unlink(pathsrc);
+        g_free(pathsrc);
+        if (op->filedst) {
+            pathdst = g_strdup_printf("%s/%s", dir, op->filedst);
+            unlink(pathdst);
+            g_free(pathdst);
+        }
+    }
+
+    qemu_file_monitor_free(mon);
+    g_list_foreach(data.records,
+                   (GFunc)qemu_file_monitor_test_record_free, NULL);
+    g_list_free(data.records);
+    qemu_mutex_destroy(&data.lock);
+    if (dir) {
+        rmdir(dir);
+    }
+    g_free(dir);
+    g_assert(err == 0);
+}
+
+
+/*
+ * Set of structs which define which file name patterns
+ * we're trying to watch against. NULL, means all files
+ * in the directory
+ */
+static const QFileMonitorTestWatch watches_any[] = {
+    { NULL },
+};
+
+static const QFileMonitorTestWatch watches_one[] = {
+    { "one.txt" },
+};
+
+static const QFileMonitorTestWatch watches_two[] = {
+    { "two.txt" },
+};
+
+static const QFileMonitorTestWatch watches_many[] = {
+    { NULL },
+    { "one.txt" },
+    { "two.txt" },
+};
+
+
+/*
+ * Various sets of file operations we're going to
+ * trigger and validate events for
+ */
+static const QFileMonitorTestOp ops_create_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", }
+};
+
+static const QFileMonitorTestOp ops_delete_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_UNLINK,
+      .filesrc = "one.txt", }
+};
+
+static const QFileMonitorTestOp ops_create_many[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "two.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "three.txt", }
+};
+
+static const QFileMonitorTestOp ops_rename_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_RENAME,
+      .filesrc = "one.txt", .filedst = "two.txt" }
+};
+
+static const QFileMonitorTestOp ops_rename_many[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "two.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_RENAME,
+      .filesrc = "one.txt", .filedst = "two.txt" }
+};
+
+static const QFileMonitorTestOp ops_append_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_APPEND,
+      .filesrc = "one.txt", },
+};
+
+static const QFileMonitorTestOp ops_trunc_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_TRUNC,
+      .filesrc = "one.txt", },
+};
+
+static const QFileMonitorTestOp ops_touch_one[] = {
+    { .type = QFILE_MONITOR_TEST_OP_CREATE,
+      .filesrc = "one.txt", },
+    { .type = QFILE_MONITOR_TEST_OP_TOUCH,
+      .filesrc = "one.txt", },
+};
+
+
+/*
+ * No we define data sets for the combinatorial
+ * expansion of file watches and operation sets
+ */
+#define PLAN_DATA(o, w) \
+    static const QFileMonitorTestPlan plan_ ## o ## _ ## w = { \
+        .nops = G_N_ELEMENTS(ops_ ##o), \
+        .ops = ops_ ##o, \
+        .nwatches = G_N_ELEMENTS(watches_ ##w), \
+        .watches = watches_ ## w, \
+    }
+
+PLAN_DATA(create_one, any);
+PLAN_DATA(create_one, one);
+PLAN_DATA(create_one, two);
+PLAN_DATA(create_one, many);
+
+PLAN_DATA(delete_one, any);
+PLAN_DATA(delete_one, one);
+PLAN_DATA(delete_one, two);
+PLAN_DATA(delete_one, many);
+
+PLAN_DATA(create_many, any);
+PLAN_DATA(create_many, one);
+PLAN_DATA(create_many, two);
+PLAN_DATA(create_many, many);
+
+PLAN_DATA(rename_one, any);
+PLAN_DATA(rename_one, one);
+PLAN_DATA(rename_one, two);
+PLAN_DATA(rename_one, many);
+
+PLAN_DATA(rename_many, any);
+PLAN_DATA(rename_many, one);
+PLAN_DATA(rename_many, two);
+PLAN_DATA(rename_many, many);
+
+PLAN_DATA(append_one, any);
+PLAN_DATA(append_one, one);
+PLAN_DATA(append_one, two);
+PLAN_DATA(append_one, many);
+
+PLAN_DATA(trunc_one, any);
+PLAN_DATA(trunc_one, one);
+PLAN_DATA(trunc_one, two);
+PLAN_DATA(trunc_one, many);
+
+PLAN_DATA(touch_one, any);
+PLAN_DATA(touch_one, one);
+PLAN_DATA(touch_one, two);
+PLAN_DATA(touch_one, many);
+
+
+int main(int argc, char **argv)
+{
+    g_test_init(&argc, &argv, NULL);
+
+    qemu_init_main_loop(&error_abort);
+
+    qemu_mutex_init(&evlock);
+
+    /*
+     * Register test cases for the combinatorial
+     * expansion of file watches and operation sets
+     */
+    #define PLAN_REGISTER(o, w)                                         \
+        g_test_add_data_func("/util/filemonitor/" # o "/" # w,          \
+                             &plan_ ## o ## _ ## w, test_file_monitor_events)
+
+    PLAN_REGISTER(create_one, any);
+    PLAN_REGISTER(create_one, one);
+    PLAN_REGISTER(create_one, two);
+    PLAN_REGISTER(create_one, many);
+
+    PLAN_REGISTER(delete_one, any);
+    PLAN_REGISTER(delete_one, one);
+    PLAN_REGISTER(delete_one, two);
+    PLAN_REGISTER(delete_one, many);
+
+    PLAN_REGISTER(create_many, any);
+    PLAN_REGISTER(create_many, one);
+    PLAN_REGISTER(create_many, two);
+    PLAN_REGISTER(create_many, many);
+
+    PLAN_REGISTER(rename_one, any);
+    PLAN_REGISTER(rename_one, one);
+    PLAN_REGISTER(rename_one, two);
+    PLAN_REGISTER(rename_one, many);
+
+    PLAN_REGISTER(rename_many, any);
+    PLAN_REGISTER(rename_many, one);
+    PLAN_REGISTER(rename_many, two);
+    PLAN_REGISTER(rename_many, many);
+
+    PLAN_REGISTER(append_one, any);
+    PLAN_REGISTER(append_one, one);
+    PLAN_REGISTER(append_one, two);
+    PLAN_REGISTER(append_one, many);
+
+    PLAN_REGISTER(trunc_one, any);
+    PLAN_REGISTER(trunc_one, one);
+    PLAN_REGISTER(trunc_one, two);
+    PLAN_REGISTER(trunc_one, many);
+
+    PLAN_REGISTER(touch_one, any);
+    PLAN_REGISTER(touch_one, one);
+    PLAN_REGISTER(touch_one, two);
+    PLAN_REGISTER(touch_one, many);
+
+    return g_test_run();
+}
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 0820923c18..c1dd746902 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -50,5 +50,8 @@ util-obj-y += range.o
 util-obj-y += stats64.o
 util-obj-y += systemd.o
 util-obj-y += iova-tree.o
+util-obj-$(CONFIG_INOTIFY1) += filemonitor-inotify.o
 util-obj-$(CONFIG_LINUX) += vfio-helpers.o
 util-obj-$(CONFIG_OPENGL) += drm.o
+
+stub-obj-y += filemonitor-stub.o
diff --git a/util/filemonitor-inotify.c b/util/filemonitor-inotify.c
new file mode 100644
index 0000000000..3a72be037f
--- /dev/null
+++ b/util/filemonitor-inotify.c
@@ -0,0 +1,339 @@
+/*
+ * QEMU file monitor Linux inotify impl
+ *
+ * Copyright (c) 2018 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 "qemu/osdep.h"
+#include "qemu/filemonitor.h"
+#include "qemu/main-loop.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+#include "trace.h"
+
+#include <sys/inotify.h>
+
+struct QFileMonitor {
+    int fd;
+
+    QemuMutex lock; /* protects dirs & idmap */
+    GHashTable *dirs; /* dirname => QFileMonitorDir */
+    GHashTable *idmap; /* inotify ID => dirname */
+};
+
+
+typedef struct {
+    int id; /* watch ID */
+    char *filename; /* optional filter */
+    QFileMonitorHandler cb;
+    void *opaque;
+} QFileMonitorWatch;
+
+
+typedef struct {
+    char *path;
+    int id; /* inotify ID */
+    int nextid; /* watch ID counter */
+    GArray *watches; /* QFileMonitorWatch elements */
+} QFileMonitorDir;
+
+
+static void qemu_file_monitor_watch(void *arg)
+{
+    QFileMonitor *mon = arg;
+    char buf[4096]
+        __attribute__ ((aligned(__alignof__(struct inotify_event))));
+    int used = 0;
+    int len;
+
+    qemu_mutex_lock(&mon->lock);
+
+    if (mon->fd == -1) {
+        qemu_mutex_unlock(&mon->lock);
+        return;
+    }
+
+    len = read(mon->fd, buf, sizeof(buf));
+
+    if (len < 0) {
+        if (errno != EAGAIN) {
+            error_report("Failure monitoring inotify FD '%s',"
+                         "disabling events", strerror(errno));
+            goto cleanup;
+        }
+
+        /* no more events right now */
+        goto cleanup;
+    }
+
+    /* Loop over all events in the buffer */
+    while (used < len) {
+        struct inotify_event *ev =
+            (struct inotify_event *)(buf + used);
+        const char *name = ev->len ? ev->name : "";
+        QFileMonitorDir *dir = g_hash_table_lookup(mon->idmap,
+                                                   GINT_TO_POINTER(ev->wd));
+        uint32_t iev = ev->mask &
+            (IN_CREATE | IN_MODIFY | IN_DELETE | IN_IGNORED |
+             IN_MOVED_TO | IN_MOVED_FROM | IN_ATTRIB);
+        int qev;
+        gsize i;
+
+        used += sizeof(struct inotify_event) + ev->len;
+
+        if (!dir) {
+            continue;
+        }
+
+        /*
+         * During a rename operation, the old name gets
+         * IN_MOVED_FROM and the new name gets IN_MOVED_TO.
+         * To simplify life for callers, we turn these into
+         * DELETED and CREATED events
+         */
+        switch (iev) {
+        case IN_CREATE:
+        case IN_MOVED_TO:
+            qev = QFILE_MONITOR_EVENT_CREATED;
+            break;
+        case IN_MODIFY:
+            qev = QFILE_MONITOR_EVENT_MODIFIED;
+            break;
+        case IN_DELETE:
+        case IN_MOVED_FROM:
+            qev = QFILE_MONITOR_EVENT_DELETED;
+            break;
+        case IN_ATTRIB:
+            qev = QFILE_MONITOR_EVENT_ATTRIBUTES;
+            break;
+        case IN_IGNORED:
+            qev = QFILE_MONITOR_EVENT_IGNORED;
+            break;
+        default:
+            g_assert_not_reached();
+        }
+
+        trace_qemu_file_monitor_event(mon, dir->path, name, ev->mask, dir->id);
+        for (i = 0; i < dir->watches->len; i++) {
+            QFileMonitorWatch *watch = &g_array_index(dir->watches,
+                                                      QFileMonitorWatch,
+                                                      i);
+
+            if (watch->filename == NULL ||
+                (name && g_str_equal(watch->filename, name))) {
+                trace_qemu_file_monitor_dispatch(mon, dir->path, name,
+                                                 qev, watch->cb,
+                                                 watch->opaque, watch->id);
+                watch->cb(watch->id, qev, name, watch->opaque);
+            }
+        }
+    }
+
+ cleanup:
+    qemu_mutex_unlock(&mon->lock);
+}
+
+
+static void
+qemu_file_monitor_dir_free(void *data)
+{
+    QFileMonitorDir *dir = data;
+    gsize i;
+
+    for (i = 0; i < dir->watches->len; i++) {
+        QFileMonitorWatch *watch = &g_array_index(dir->watches,
+                                                  QFileMonitorWatch, i);
+        g_free(watch->filename);
+    }
+    g_array_unref(dir->watches);
+    g_free(dir->path);
+    g_free(dir);
+}
+
+
+QFileMonitor *
+qemu_file_monitor_new(Error **errp)
+{
+    int fd;
+    QFileMonitor *mon;
+
+    fd = inotify_init1(IN_NONBLOCK);
+    if (fd < 0) {
+        error_setg_errno(errp, errno,
+                         "Unable to initialize inotify");
+        return NULL;
+    }
+
+    mon = g_new0(QFileMonitor, 1);
+    qemu_mutex_init(&mon->lock);
+    mon->fd = fd;
+
+    mon->dirs = g_hash_table_new_full(g_str_hash, g_str_equal, NULL,
+                                      qemu_file_monitor_dir_free);
+    mon->idmap = g_hash_table_new(g_direct_hash, g_direct_equal);
+
+    trace_qemu_file_monitor_new(mon, mon->fd);
+
+    return mon;
+}
+
+static gboolean
+qemu_file_monitor_free_idle(void *opaque)
+{
+    QFileMonitor *mon = opaque;
+
+    if (!mon) {
+        return G_SOURCE_REMOVE;
+    }
+
+    qemu_mutex_lock(&mon->lock);
+
+    g_hash_table_unref(mon->idmap);
+    g_hash_table_unref(mon->dirs);
+
+    qemu_mutex_unlock(&mon->lock);
+
+    qemu_mutex_destroy(&mon->lock);
+    g_free(mon);
+
+    return G_SOURCE_REMOVE;
+}
+
+void
+qemu_file_monitor_free(QFileMonitor *mon)
+{
+    if (!mon) {
+        return;
+    }
+
+    qemu_mutex_lock(&mon->lock);
+    if (mon->fd != -1) {
+        qemu_set_fd_handler(mon->fd, NULL, NULL, NULL);
+        close(mon->fd);
+        mon->fd = -1;
+    }
+    qemu_mutex_unlock(&mon->lock);
+
+    /*
+     * Can't free it yet, because another thread
+     * may be running event loop, so the inotify
+     * callback might be pending. Using an idle
+     * source ensures we'll only free after the
+     * pending callback is done
+     */
+    g_idle_add((GSourceFunc)qemu_file_monitor_free_idle, mon);
+}
+
+int
+qemu_file_monitor_add_watch(QFileMonitor *mon,
+                            const char *dirpath,
+                            const char *filename,
+                            QFileMonitorHandler cb,
+                            void *opaque,
+                            Error **errp)
+{
+    QFileMonitorDir *dir;
+    QFileMonitorWatch watch;
+    int ret = -1;
+
+    qemu_mutex_lock(&mon->lock);
+    dir = g_hash_table_lookup(mon->dirs, dirpath);
+    if (!dir) {
+        int rv = inotify_add_watch(mon->fd, dirpath,
+                                   IN_CREATE | IN_DELETE | IN_MODIFY |
+                                   IN_MOVED_TO | IN_MOVED_FROM | IN_ATTRIB);
+
+        if (rv < 0) {
+            error_setg_errno(errp, errno, "Unable to watch '%s'", dirpath);
+            goto cleanup;
+        }
+
+        trace_qemu_file_monitor_enable_watch(mon, dirpath, rv);
+
+        dir = g_new0(QFileMonitorDir, 1);
+        dir->path = g_strdup(dirpath);
+        dir->id = rv;
+        dir->watches = g_array_new(FALSE, TRUE, sizeof(QFileMonitorWatch));
+
+        g_hash_table_insert(mon->dirs, dir->path, dir);
+        g_hash_table_insert(mon->idmap, GINT_TO_POINTER(rv), dir);
+
+        if (g_hash_table_size(mon->dirs) == 1) {
+            qemu_set_fd_handler(mon->fd, qemu_file_monitor_watch, NULL, mon);
+        }
+    }
+
+    watch.id = dir->nextid++;
+    watch.filename = g_strdup(filename);
+    watch.cb = cb;
+    watch.opaque = opaque;
+
+    g_array_append_val(dir->watches, watch);
+
+    trace_qemu_file_monitor_add_watch(mon, dirpath,
+                                      filename ? filename : "<none>",
+                                      cb, opaque, watch.id);
+
+    ret = watch.id;
+
+ cleanup:
+    qemu_mutex_unlock(&mon->lock);
+    return ret;
+}
+
+
+void qemu_file_monitor_remove_watch(QFileMonitor *mon,
+                                    const char *dirpath,
+                                    int id)
+{
+    QFileMonitorDir *dir;
+    gsize i;
+
+    qemu_mutex_lock(&mon->lock);
+
+    trace_qemu_file_monitor_remove_watch(mon, dirpath, id);
+
+    dir = g_hash_table_lookup(mon->dirs, dirpath);
+    if (!dir) {
+        goto cleanup;
+    }
+
+    for (i = 0; i < dir->watches->len; i++) {
+        QFileMonitorWatch *watch = &g_array_index(dir->watches,
+                                                  QFileMonitorWatch, i);
+        if (watch->id == id) {
+            g_free(watch->filename);
+            g_array_remove_index(dir->watches, i);
+            break;
+        }
+    }
+
+    if (dir->watches->len == 0) {
+        inotify_rm_watch(mon->fd, dir->id);
+        trace_qemu_file_monitor_disable_watch(mon, dir->path, dir->id);
+
+        g_hash_table_remove(mon->idmap, GINT_TO_POINTER(dir->id));
+        g_hash_table_remove(mon->dirs, dir->path);
+
+        if (g_hash_table_size(mon->dirs) == 0) {
+            qemu_set_fd_handler(mon->fd, NULL, NULL, NULL);
+        }
+    }
+
+ cleanup:
+    qemu_mutex_unlock(&mon->lock);
+}
diff --git a/util/filemonitor-stub.c b/util/filemonitor-stub.c
new file mode 100644
index 0000000000..48268b2bb6
--- /dev/null
+++ b/util/filemonitor-stub.c
@@ -0,0 +1,59 @@
+/*
+ * QEMU file monitor stub impl
+ *
+ * Copyright (c) 2018 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 "qemu/osdep.h"
+#include "qemu/filemonitor.h"
+#include "qemu/error-report.h"
+#include "qapi/error.h"
+
+
+QFileMonitor *
+qemu_file_monitor_new(Error **errp)
+{
+    error_setg(errp, "File monitoring not available on this platform");
+    return NULL;
+}
+
+
+void
+qemu_file_monitor_free(QFileMonitor *mon G_GNUC_UNUSED)
+{
+}
+
+
+int
+qemu_file_monitor_add_watch(QFileMonitor *mon G_GNUC_UNUSED,
+                            const char *dirpath G_GNUC_UNUSED,
+                            const char *filename G_GNUC_UNUSED,
+                            QFileMonitorHandler cb G_GNUC_UNUSED,
+                            void *opaque G_GNUC_UNUSED,
+                            Error **errp)
+{
+    error_setg(errp, "File monitoring not available on this platform");
+    return -1;
+}
+
+
+void
+qemu_file_monitor_remove_watch(QFileMonitor *mon G_GNUC_UNUSED,
+                               const char *dirpath G_GNUC_UNUSED,
+                               int id G_GNUC_UNUSED)
+{
+}
diff --git a/util/trace-events b/util/trace-events
index 79569b7fdf..ff19b253e2 100644
--- a/util/trace-events
+++ b/util/trace-events
@@ -21,6 +21,15 @@ buffer_move_empty(const char *buf, size_t len, const char *from) "%s: %zd bytes
 buffer_move(const char *buf, size_t len, const char *from) "%s: %zd bytes from %s"
 buffer_free(const char *buf, size_t len) "%s: capacity %zd"
 
+# util/filemonitor.c
+qemu_file_monitor_add_watch(void *mon, const char *dirpath, const char *filename, void *cb, void *opaque, int id) "File monitor %p add watch dir='%s' file='%s' cb=%p opaque=%p id=%u"
+qemu_file_monitor_remove_watch(void *mon, const char *dirpath, int id) "File monitor %p remove watch dir='%s' id=%u"
+qemu_file_monitor_new(void *mon, int fd) "File monitor %p created fd=%d"
+qemu_file_monitor_enable_watch(void *mon, const char *dirpath, int id) "File monitor %p enable watch dir='%s' id=%u"
+qemu_file_monitor_disable_watch(void *mon, const char *dirpath, int id) "Fle monitor %p disable watch dir='%s' id=%u"
+qemu_file_monitor_event(void *mon, const char *dirpath, const char *filename, int mask, unsigned int id) "File monitor %p event dir='%s' file='%s' mask=0x%x id=%u"
+qemu_file_monitor_dispatch(void *mon, const char *dirpath, const char *filename, int ev, void *cb, void *opaque, unsigned int id) "File monitor %p dispatch dir='%s' file='%s' ev=%d cb=%p opaque=%p id=%u"
+
 # util/qemu-coroutine.c
 qemu_aio_coroutine_enter(void *ctx, void *from, void *to, void *opaque) "ctx %p from %p to %p opaque %p"
 qemu_coroutine_yield(void *from, void *to) "from %p to %p"