Re: [Qemu-devel] [PATCH v6 01/11] util: add helper APIs for dealing with inotify in portable manner

[Marc-André Lureau]

Hi

On Fri, Oct 19, 2018 at 5:41 PM Daniel P. Berrangé <address@hidden> wrote:
>
> 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.
>
> Signed-off-by: Daniel P. Berrangé <address@hidden>
> ---
>  include/qemu/filemonitor.h | 117 ++++++++++++++
>  util/filemonitor.c         | 315 +++++++++++++++++++++++++++++++++++++
>  MAINTAINERS                |   6 +
>  util/Makefile.objs         |   1 +
>  util/trace-events          |   9 ++
>  5 files changed, 448 insertions(+)
>  create mode 100644 include/qemu/filemonitor.h
>  create mode 100644 util/filemonitor.c
>
> diff --git a/include/qemu/filemonitor.h b/include/qemu/filemonitor.h
> new file mode 100644
> index 0000000000..1326272f0a
> --- /dev/null
> +++ b/include/qemu/filemonitor.h
> @@ -0,0 +1,117 @@
> +/*
> + * 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,
> +    /* 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_get_instance:
> + * @errp: pointer to a NULL-initialized error object
> + *
> + * Acquire a handle to the shared 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 shared monitoring object, or NULL on error
> + */
> +QFileMonitor *qemu_file_monitor_get_instance(Error **errp);
> +
> +/**
> + * 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/util/filemonitor.c b/util/filemonitor.c
> new file mode 100644
> index 0000000000..67d7aedbe0
> --- /dev/null
> +++ b/util/filemonitor.c
> @@ -0,0 +1,315 @@
> +/*
> + * 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/>.
> + *
> + */
> +
> +#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"
> +
> +struct QFileMonitor {
> +    QemuMutex lock;
> +    int fd;
> +
> +    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 */
> +    gsize nwatches;
> +    QFileMonitorWatch *watches;
> +} QFileMonitorDir;
> +
> +
> +#ifdef CONFIG_INOTIFY1
> +#include <sys/inotify.h>
> +
> +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 = read(mon->fd, buf, sizeof(buf));
> +
> +    qemu_mutex_lock(&mon->lock);

I suppose the lock should guard from mon->fd above, or there might be
a race when modifying/removing a watch from a different thread.

> +
> +    if (len < 0) {
> +        if (errno != EAGAIN) {
> +            error_report("Failure monitoring inotify FD, disabling events");

strerror(errno) could be useful

> +            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);
> +        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_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->nwatches; i++) {
> +            QFileMonitorWatch *watch = &dir->watches[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;
> +
> +    g_free(dir->watches);

for sake, I would add
assert(dir->nwatches = 0)

> +    g_free(dir);
> +}
> +
> +#endif
> +
> +static QFileMonitor *
> +qemu_file_monitor_new(Error **errp)
> +{
> +#ifdef CONFIG_INOTIFY1
> +    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;
> +#else
> +    error_setg(errp, "File monitoring not available on this platform");
> +    return NULL;
> +#endif
> +}
> +
> +
> +QFileMonitor *qemu_file_monitor_get_instance(Error **errp)
> +{
> +    static QFileMonitor *global;
> +
> +    if (!global) {
> +        global = qemu_file_monitor_new(errp);
> +    }
> +
> +    return global;
> +}
> +
> +
> +#ifdef CONFIG_INOTIFY1
> +int
> +qemu_file_monitor_add_watch(QFileMonitor *mon,
> +                            const char *dirpath,
> +                            const char *filename,
> +                            QFileMonitorHandler cb,
> +                            void *opaque,
> +                            Error **errp)
> +{
> +    QFileMonitorDir *dir;
> +    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);
> +
> +        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;
> +
> +        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);
> +        }
> +    }
> +
> +    dir->watches = g_renew(QFileMonitorWatch, dir->watches, dir->nwatches + 
> 1);

GArray could eventually make handling of watches a bit simpler
(counting, resizing, removing etc)

> +
> +    dir->watches[dir->nwatches].id = ++dir->nextid;
> +    dir->watches[dir->nwatches].filename = filename ? g_strdup(filename) : 
> NULL;

g_strdup(NULL) returns NULL already

> +    dir->watches[dir->nwatches].cb = cb;
> +    dir->watches[dir->nwatches].opaque = opaque;
> +    dir->nwatches++;
> +
> +    trace_qemu_file_monitor_add_watch(mon, dirpath,
> +                                      filename ? filename : "<none>",
> +                                      cb, opaque,
> +                                      dir->watches[dir->nwatches - 1].id);
> +
> +    ret = 0;
> +
> + 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->nwatches; i++) {
> +        if (dir->watches[i].id == id) {
> +            if (i < (dir->nwatches - 1)) {
> +                memmove(dir->watches + i,
> +                        dir->watches + i + 1,
> +                        sizeof(QFileMonitorWatch) *
> +                        (dir->nwatches - (i + 1)));
> +                dir->watches = g_renew(QFileMonitorWatch, dir->watches,
> +                                       dir->nwatches - 1);
> +                dir->nwatches--;
> +            }
> +            break;
> +        }
> +    }
> +
> +    if (dir->nwatches == 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);
> +    }
> +
> + cleanup:
> +    qemu_mutex_lock(&mon->lock);
> +}
> +
> +#else
> +int
> +qemu_file_monitor_add_watch(QFileMonitor *mon,
> +                            const char *dirpath,
> +                            const char *filename,
> +                            QFileMonitorHandler cb,
> +                            void *opaque,
> +                            Error **errp)
> +{
> +    error_setg(errp, "File monitoring not available on this platform");
> +    return -1;
> +}
> +
> +void qemu_file_monitor_remove_watch(QFileMonitor *mon,
> +                                    const char *dirpath,
> +                                    int id)
> +{
> +}

Wouldn't it be cleaner with stubs/ ?

> +#endif
> +
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 40672c4eba..29bbcf8c25 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1866,6 +1866,12 @@ F: include/qemu/sockets.h
>  F: util/qemu-sockets.c
>  F: qapi/sockets.json
>
> +File monitor
> +M: Daniel P. Berrange <address@hidden>
> +S: Odd fixes
> +F: util/filemonitor.c
> +F: include/qemu/filemonitor.h
> +
>  Throttling infrastructure
>  M: Alberto Garcia <address@hidden>
>  S: Supported
> diff --git a/util/Makefile.objs b/util/Makefile.objs
> index 0820923c18..4d7675d6e7 100644
> --- a/util/Makefile.objs
> +++ b/util/Makefile.objs
> @@ -50,5 +50,6 @@ util-obj-y += range.o
>  util-obj-y += stats64.o
>  util-obj-y += systemd.o
>  util-obj-y += iova-tree.o
> +util-obj-y += filemonitor.o
>  util-obj-$(CONFIG_LINUX) += vfio-helpers.o
>  util-obj-$(CONFIG_OPENGL) += drm.o
> 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"
> --
> 2.17.2
>
>

Looks good, but would be even better with tests :)

-- 
Marc-André Lureau