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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#include "bus-util.h"
#include "device-util.h"
#include "hash-funcs.h"
#include "logind-brightness.h"
#include "logind.h"
#include "process-util.h"
#include "stdio-util.h"
/* Brightness and LED devices tend to be very slow to write to (often being I2C and such). Writes to the
* sysfs attributes are synchronous, and hence will freeze our process on access. We can't really have that,
* hence we add some complexity: whenever we need to write to the brightness attribute, we do so in a forked
* off process, which terminates when it is done. Watching that process allows us to watch completion of the
* write operation.
*
* To make this even more complex: clients are likely to send us many write requests in a short time-frame
* (because they implement reactive brightness sliders on screen). Let's coalesce writes to make this
* efficient: whenever we get requests to change brightness while we are still writing to the brightness
* attribute, let's remember the request and restart a new one when the initial operation finished. When we
* get another request while one is ongoing and one is pending we'll replace the pending one with the new
* one.
*
* The bus messages are answered when the first write operation finishes that started either due to the
* request or due to a later request that overrode the requested one.
*
* Yes, this is complex, but I don't see an easier way if we want to be both efficient and still support
* completion notification. */
typedef struct BrightnessWriter {
Manager *manager;
sd_device *device;
char *path;
pid_t child;
uint32_t brightness;
bool again;
Set *current_messages;
Set *pending_messages;
sd_event_source* child_event_source;
} BrightnessWriter;
static BrightnessWriter* brightness_writer_free(BrightnessWriter *w) {
if (!w)
return NULL;
if (w->manager && w->path)
(void) hashmap_remove_value(w->manager->brightness_writers, w->path, w);
sd_device_unref(w->device);
free(w->path);
set_free(w->current_messages);
set_free(w->pending_messages);
w->child_event_source = sd_event_source_unref(w->child_event_source);
return mfree(w);
}
DEFINE_TRIVIAL_CLEANUP_FUNC(BrightnessWriter*, brightness_writer_free);
DEFINE_PRIVATE_HASH_OPS_WITH_VALUE_DESTRUCTOR(
brightness_writer_hash_ops,
char,
string_hash_func,
string_compare_func,
BrightnessWriter,
brightness_writer_free);
static void brightness_writer_reply(BrightnessWriter *w, int error) {
int r;
assert(w);
for (;;) {
_cleanup_(sd_bus_message_unrefp) sd_bus_message *m = NULL;
m = set_steal_first(w->current_messages);
if (!m)
break;
if (error == 0)
r = sd_bus_reply_method_return(m, NULL);
else
r = sd_bus_reply_method_errnof(m, error, "Failed to write to brightness device: %m");
if (r < 0)
log_warning_errno(r, "Failed to send method reply, ignoring: %m");
}
}
static int brightness_writer_fork(BrightnessWriter *w);
static int on_brightness_writer_exit(sd_event_source *s, const siginfo_t *si, void *userdata) {
BrightnessWriter *w = ASSERT_PTR(userdata);
int r;
assert(s);
assert(si);
assert(si->si_pid == w->child);
w->child = 0;
w->child_event_source = sd_event_source_unref(w->child_event_source);
brightness_writer_reply(w,
si->si_code == CLD_EXITED &&
si->si_status == EXIT_SUCCESS ? 0 : -EPROTO);
if (w->again) {
/* Another request to change the brightness has been queued. Act on it, but make the pending
* messages the current ones. */
w->again = false;
set_free(w->current_messages);
w->current_messages = TAKE_PTR(w->pending_messages);
r = brightness_writer_fork(w);
if (r >= 0)
return 0;
brightness_writer_reply(w, r);
}
brightness_writer_free(w);
return 0;
}
static int brightness_writer_fork(BrightnessWriter *w) {
int r;
assert(w);
assert(w->manager);
assert(w->child == 0);
assert(!w->child_event_source);
r = safe_fork("(sd-bright)", FORK_DEATHSIG_SIGKILL|FORK_REARRANGE_STDIO|FORK_CLOSE_ALL_FDS|FORK_LOG|FORK_REOPEN_LOG, &w->child);
if (r < 0)
return r;
if (r == 0) {
char brs[DECIMAL_STR_MAX(uint32_t)+1];
/* Child */
xsprintf(brs, "%" PRIu32, w->brightness);
r = sd_device_set_sysattr_value(w->device, "brightness", brs);
if (r < 0) {
log_device_error_errno(w->device, r, "Failed to write brightness to device: %m");
_exit(EXIT_FAILURE);
}
_exit(EXIT_SUCCESS);
}
r = sd_event_add_child(w->manager->event, &w->child_event_source, w->child, WEXITED, on_brightness_writer_exit, w);
if (r < 0)
return log_error_errno(r, "Failed to watch brightness writer child " PID_FMT ": %m", w->child);
return 0;
}
static int set_add_message(Set **set, sd_bus_message *message) {
int r;
assert(set);
if (!message)
return 0;
r = sd_bus_message_get_expect_reply(message);
if (r <= 0)
return r;
r = set_ensure_put(set, &bus_message_hash_ops, message);
if (r <= 0)
return r;
sd_bus_message_ref(message);
return 1;
}
int manager_write_brightness(
Manager *m,
sd_device *device,
uint32_t brightness,
sd_bus_message *message) {
_cleanup_(brightness_writer_freep) BrightnessWriter *w = NULL;
BrightnessWriter *existing;
const char *path;
int r;
assert(m);
assert(device);
r = sd_device_get_syspath(device, &path);
if (r < 0)
return log_device_error_errno(device, r, "Failed to get sysfs path for brightness device: %m");
existing = hashmap_get(m->brightness_writers, path);
if (existing) {
/* There's already a writer for this device. Let's update it with the new brightness, and add
* our message to the set of message to reply when done. */
r = set_add_message(&existing->pending_messages, message);
if (r < 0)
return log_error_errno(r, "Failed to add message to set: %m");
/* We override any previously requested brightness here: we coalesce writes, and the newest
* requested brightness is the one we'll put into effect. */
existing->brightness = brightness;
existing->again = true; /* request another iteration of the writer when the current one is
* complete */
return 0;
}
w = new(BrightnessWriter, 1);
if (!w)
return log_oom();
*w = (BrightnessWriter) {
.device = sd_device_ref(device),
.path = strdup(path),
.brightness = brightness,
};
if (!w->path)
return log_oom();
r = hashmap_ensure_put(&m->brightness_writers, &brightness_writer_hash_ops, w->path, w);
if (r == -ENOMEM)
return log_oom();
if (r < 0)
return log_error_errno(r, "Failed to add brightness writer to hashmap: %m");
w->manager = m;
r = set_add_message(&w->current_messages, message);
if (r < 0)
return log_error_errno(r, "Failed to add message to set: %m");
r = brightness_writer_fork(w);
if (r < 0)
return r;
TAKE_PTR(w);
return 0;
}
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