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spa: v4l2: use a separate watch for each device

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Instead of watching /dev, use a separate watch for each device.
This is supposed to achieve the same result as the now reverted
88f0dbd6fc ("v4l2: don't set inotify on /dev"):

  Doing inotify on /dev is not a good idea because we will be woken up by
  a lot of unrelated events.

  There is a report of a performance regression on some IO benchmark
  because of lock contention within the fsnotify subsystem due to this.

  Instead, just watch for attribute changes on the /dev/videoX files
  directly. We are only interested in attribute changes, udev should
  notify us when the file is added or removed.

Fixes #3439
This commit is contained in:
Barnabás Pőcze 2023-09-07 02:10:04 +02:00 • committed by Wim Taymans
parent 53ce1ee576
commit 3bbccccd05
1 changed files with 51 additions and 34 deletions
Download patch file Download diff file Expand all files Collapse all files

85
spa/plugins/v4l2/v4l2-udev.c
View file

@ -35,6 +35,7 @@
struct device {
uint32_t id;
struct udev_device *dev;
int inotify_wd;
unsigned int accessible:1;
unsigned int ignored:1;
unsigned int emitted:1;
@ -80,6 +81,28 @@ static int impl_udev_close(struct impl *this)
return 0;
}
static void start_watching_device(struct impl *this, struct device *device)
{
if (this->notify.fd < 0 || device->inotify_wd >= 0)
return;
char path[64];
snprintf(path, sizeof(path), "/dev/video%" PRIu32, device->id);
device->inotify_wd = inotify_add_watch(this->notify.fd, path, IN_ATTRIB);
}
static void stop_watching_device(struct impl *this, struct device *device)
{
if (device->inotify_wd < 0)
return;
spa_assert(this->notify.fd >= 0);
inotify_rm_watch(this->notify.fd, device->inotify_wd);
device->inotify_wd = -1;
}
static struct device *add_device(struct impl *this, uint32_t id, struct udev_device *dev)
{
struct device *device;
@ -91,6 +114,10 @@ static struct device *add_device(struct impl *this, uint32_t id, struct udev_dev
device->id = id;
udev_device_ref(dev);
device->dev = dev;
device->inotify_wd = -1;
start_watching_device(this, device);
return device;
}
@ -106,16 +133,15 @@ static struct device *find_device(struct impl *this, uint32_t id)
static void remove_device(struct impl *this, struct device *device)
{
udev_device_unref(device->dev);
device->dev = udev_device_unref(device->dev);
stop_watching_device(this, device);
*device = this->devices[--this->n_devices];
}
static void clear_devices(struct impl *this)
{
uint32_t i;
for (i = 0; i < this->n_devices; i++)
udev_device_unref(this->devices[i].dev);
this->n_devices = 0;
while (this->n_devices > 0)
remove_device(this, &this->devices[0]);
}
static uint32_t get_device_id(struct impl *this, struct udev_device *dev)
@ -381,6 +407,10 @@ static int stop_inotify(struct impl *this)
if (this->notify.fd == -1)
return 0;
spa_log_info(this->log, "stop inotify");
for (size_t i = 0; i < this->n_devices; i++)
stop_watching_device(this, &this->devices[i]);
spa_loop_remove_source(this->main_loop, &this->notify);
close(this->notify.fd);
this->notify.fd = -1;
@ -389,7 +419,6 @@ static int stop_inotify(struct impl *this)
static void impl_on_notify_events(struct spa_source *source)
{
bool deleted = false;
struct impl *this = source->data;
union {
unsigned char name[sizeof(struct inotify_event) + NAME_MAX + 1];
@ -411,35 +440,33 @@ static void impl_on_notify_events(struct spa_source *source)
for (p = &buf; p < e;
p = SPA_PTROFF(p, sizeof(struct inotify_event) + event->len, void)) {
unsigned int id;
struct device *device;
event = (const struct inotify_event *) p;
if ((event->mask & IN_ATTRIB)) {
bool access;
if (sscanf(event->name, "video%u", &id) != 1)
continue;
if ((device = find_device(this, id)) == NULL)
continue;
access = check_access(this, device);
struct device *device = NULL;
for (size_t i = 0; i < this->n_devices; i++) {
if (this->devices[i].inotify_wd == event->wd) {
device = &this->devices[i];
break;
}
}
spa_assert(device);
bool access = check_access(this, device);
if (access && !device->emitted)
process_device(this, ACTION_ADD, device->dev);
else if (!access && device->emitted)
process_device(this, ACTION_DISABLE, device->dev);
}
/* /dev/ might have been removed */
if ((event->mask & (IN_DELETE_SELF | IN_MOVE_SELF)))
deleted = true;
}
}
if (deleted)
stop_inotify(this);
}
static int start_inotify(struct impl *this)
{
int res, notify_fd;
int notify_fd;
if (this->notify.fd != -1)
return 0;
@ -447,19 +474,6 @@ static int start_inotify(struct impl *this)
if ((notify_fd = inotify_init1(IN_CLOEXEC | IN_NONBLOCK)) < 0)
return -errno;
res = inotify_add_watch(notify_fd, "/dev",
IN_ATTRIB | IN_CLOSE_WRITE | IN_DELETE_SELF | IN_MOVE_SELF);
if (res < 0) {
res = -errno;
close(notify_fd);
if (res == -ENOENT) {
spa_log_debug(this->log, "/dev/ does not exist yet");
return 0;
}
spa_log_error(this->log, "inotify_add_watch() failed: %s", spa_strerror(res));
return res;
}
spa_log_info(this->log, "start inotify");
this->notify.func = impl_on_notify_events;
this->notify.data = this;
@ -468,6 +482,9 @@ static int start_inotify(struct impl *this)
spa_loop_add_source(this->main_loop, &this->notify);
for (size_t i = 0; i < this->n_devices; i++)
start_watching_device(this, &this->devices[i]);
return 0;
}