qemu/util/filemonitor-inotify.c
Daniel P. Berrangé b4682a63f8 filemon: fix watch IDs to avoid potential wraparound issues
Watch IDs are allocated from incrementing a int counter against
the QFileMonitor object. In very long life QEMU processes with
a huge amount of USB MTP activity creating & deleting directories
it is just about conceivable that the int counter can wrap
around. This would result in incorrect behaviour of the file
monitor watch APIs due to clashing watch IDs.

Instead of trying to detect this situation, this patch changes
the way watch IDs are allocated. It is turned into an int64_t
variable where the high 32 bits are set from the underlying
inotify "int" ID. This gives an ID that is guaranteed unique
for the directory as a whole, and we can rely on the kernel
to enforce this. QFileMonitor then sets the low 32 bits from
a per-directory counter.

The USB MTP device only sets watches on the directory as a
whole, not files within, so there is no risk of guest
triggered wrap around on the low 32 bits.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
2019-04-02 13:52:02 +01:00

340 lines
9.2 KiB
C

/*
* 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 {
int64_t id; /* watch ID */
char *filename; /* optional filter */
QFileMonitorHandler cb;
void *opaque;
} QFileMonitorWatch;
typedef struct {
char *path;
int inotify_id; /* inotify ID */
int next_file_id; /* file 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->inotify_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);
}
int64_t
qemu_file_monitor_add_watch(QFileMonitor *mon,
const char *dirpath,
const char *filename,
QFileMonitorHandler cb,
void *opaque,
Error **errp)
{
QFileMonitorDir *dir;
QFileMonitorWatch watch;
int64_t 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->inotify_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 = (((int64_t)dir->inotify_id) << 32) | dir->next_file_id++;
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,
int64_t 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->inotify_id);
trace_qemu_file_monitor_disable_watch(mon, dir->path, dir->inotify_id);
g_hash_table_remove(mon->idmap, GINT_TO_POINTER(dir->inotify_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);
}