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Move to smi version 10, read-only interface, no mutex, write and read each record twice to ensure it is not inconsistent when read.

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This commit is contained in:
Mike Brady
2023-09-11 16:02:49 +01:00
parent b7d9c22de9
commit dabfee5bac
4 changed files with 122 additions and 44 deletions
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nqptp-shm-structures.h
+13 -7
View File
@@ -22,7 +22,7 @@
#define NQPTP_INTERFACE_NAME "/nqptp"
#define NQPTP_SHM_STRUCTURES_VERSION 9
#define NQPTP_SHM_STRUCTURES_VERSION 10
#define NQPTP_CONTROL_PORT 9000
// The control port expects a UDP packet with the first character being a command letter
@@ -50,20 +50,26 @@
// When the clock is inactive, it can stop running. This causes the offset to decrease.
// NQPTP clock smoothing would treat this as a network delay, causing true sync to be lost.
// To avoid this, when the clock goes from inactive to active,
// NQPTP resets clock smoothing to the new offset.
// NQPTP resets clock smoothing to the new offset.
#include <inttypes.h>
#include <pthread.h>
struct shm_structure {
pthread_mutex_t shm_mutex; // for safely accessing the structure
uint16_t version; // check this is equal to NQPTP_SHM_STRUCTURES_VERSION
typedef struct {
uint64_t master_clock_id; // the current master clock
char master_clock_ip[64]; // where it's coming from
uint64_t local_time; // the time when the offset was calculated
uint64_t local_to_master_time_offset; // add this to the local time to get master clock time
uint64_t master_clock_start_time; // this is when the master clock became master
} shm_structure_set;
// The secondary record must be written strictly after all writes to the main record are
// complete.
// This is ensured using the __sync_synchronize() construct.
// The reader should ensure that both copies match for a read to be valid.
struct shm_structure {
uint16_t version; // check this is equal to NQPTP_SHM_STRUCTURES_VERSION
shm_structure_set main;
shm_structure_set secondary;
};
#endif
ptp-utilities.c
+63 -16
View File
@@ -1,6 +1,6 @@
/*
* This file is part of Shairport Sync.
* Copyright (c) Mike Brady 2020 -- 2021
* Copyright (c) Mike Brady 2020 -- 2023
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person
@@ -49,23 +49,70 @@ void *mapped_addr = NULL;
// returns a copy of the shared memory data from the nqptp
// shared memory interface, so long as it's open.
int get_nqptp_data(struct shm_structure *nqptp_data) {
// uint64_t tn = get_absolute_time_in_ns(); // if interested in timing the function...
struct shm_structure local_nqptp_data;
int response = -1; // presume the worst. Fix it on success
// the first part of the shared memory is a mutex lock, so use it to get
// exclusive access while copying
// We need to ensure that when we read the record, we are not reading it while it is partly
// updated and therefore inconsistent. To achieve this, we do the following:
// We ensure that the secondary record is written by NQPTP _strictly after_
// all writes to the main record are complete.
// Here we read two copies of the entire record, the second
// _strictly after_ all reads from the first are complete.
// (Strict write and read ordering is ensured using the __sync_synchronize() construct.)
// We then compare the main record in the first read to the
// secondary record in the second read.
// If they are equal, we can be sure we have not read a record that has been
// made inconsistent by an interrupted update.
if ((mapped_addr != MAP_FAILED) && (mapped_addr != NULL)) {
pthread_cleanup_debug_mutex_lock((pthread_mutex_t *)mapped_addr, 10000, 1);
memcpy(nqptp_data, (char *)mapped_addr, sizeof(struct shm_structure));
pthread_cleanup_pop(1); // release the mutex
response = 0;
int loop_count = 1;
do {
__sync_synchronize();
memcpy(nqptp_data, (char *)mapped_addr, sizeof(struct shm_structure));
__sync_synchronize();
// read again strictly after a full read -- this is to read the secondary strictly after the
// primary
memcpy(&local_nqptp_data, (char *)mapped_addr, sizeof(struct shm_structure));
// check that the main and secondary data sets match
if (memcmp(&nqptp_data->main, &local_nqptp_data.secondary, sizeof(shm_structure_set)) != 0) {
usleep(2); // microseconds
loop_count++;
}
} while (
(memcmp(&nqptp_data->main, &local_nqptp_data.secondary, sizeof(shm_structure_set)) != 0) &&
(loop_count < 100));
if (loop_count == 10) {
debug(1, "get_nqptp_data -- main and secondary records don't match after %d attempts!",
loop_count);
response = -1;
} else {
response = 0;
}
} else {
if (mapped_addr == NULL)
debug(1, "get_nqptp_data because the mapped_addr is NULL");
debug(1, "get_nqptp_data failed because the mapped_addr is NULL");
else if (mapped_addr == MAP_FAILED)
debug(1, "get_nqptp_data because the mapped_addr is MAP_FAILED");
debug(1, "get_nqptp_data failed because the mapped_addr is MAP_FAILED");
else
debug(1, "get_nqptp_data failed");
}
// int64_t et = get_absolute_time_in_ns() - tn;
// debug(1, "get_nqptp_data time: %.3f microseconds.", 0.001 * et);
return response;
}
int ptp_get_clock_version() {
int response = 0; // no version number information available
struct shm_structure nqptp_data;
if (get_nqptp_data(&nqptp_data) == 0) {
response = nqptp_data.version;
}
return response;
}
@@ -85,15 +132,15 @@ int ptp_get_clock_info(uint64_t *actual_clock_id, uint64_t *time_of_sample, uint
if (get_nqptp_data(&nqptp_data) == 0) {
if (nqptp_data.version == NQPTP_SHM_STRUCTURES_VERSION) {
// assuming a clock id can not be zero
if (nqptp_data.master_clock_id != 0) {
if (nqptp_data.main.master_clock_id != 0) {
if (actual_clock_id != NULL)
*actual_clock_id = nqptp_data.master_clock_id;
*actual_clock_id = nqptp_data.main.master_clock_id;
if (time_of_sample != NULL)
*time_of_sample = nqptp_data.local_time;
*time_of_sample = nqptp_data.main.local_time;
if (raw_offset != NULL)
*raw_offset = nqptp_data.local_to_master_time_offset;
*raw_offset = nqptp_data.main.local_to_master_time_offset;
if (mastership_start_time != NULL)
*mastership_start_time = nqptp_data.master_clock_start_time;
*mastership_start_time = nqptp_data.main.master_clock_start_time;
} else {
response = clock_no_master;
}
@@ -124,12 +171,12 @@ int ptp_shm_interface_open() {
if (strcmp(config.nqptp_shared_memory_interface_name, "") != 0) {
response = 0;
int shared_memory_file_descriptor =
shm_open(config.nqptp_shared_memory_interface_name, O_RDWR, 0);
shm_open(config.nqptp_shared_memory_interface_name, O_RDONLY, 0);
if (shared_memory_file_descriptor >= 0) {
mapped_addr =
// needs to be PROT_READ | PROT_WRITE to allow the mapped memory to be writable for the
// mutex to lock and unlock
mmap(NULL, sizeof(struct shm_structure), PROT_READ | PROT_WRITE, MAP_SHARED,
mmap(NULL, sizeof(struct shm_structure), PROT_READ, MAP_SHARED,
shared_memory_file_descriptor, 0);
if (mapped_addr == MAP_FAILED) {
response = -1;
ptp-utilities.h
+2 -1
View File
@@ -1,6 +1,6 @@
/*
* This file is part of Shairport Sync.
* Copyright (c) Mike Brady 2020 -- 2021
* Copyright (c) Mike Brady 2020 -- 2023
* All rights reserved.
*
* Permission is hereby granted, free of charge, to any person
@@ -37,6 +37,7 @@ void ptp_send_control_message_string(const char *msg);
void ptp_shm_interface_init();
int ptp_shm_interface_open();
int ptp_get_clock_version();
int ptp_shm_interface_close();
#endif /* __PTP_UTILITIES_H */
shairport.c
+44 -20
View File
@@ -61,8 +61,8 @@
#endif
#ifdef CONFIG_OPENSSL
#include <openssl/md5.h>
#include <openssl/evp.h>
#include <openssl/md5.h>
#endif
#if defined(CONFIG_DBUS_INTERFACE)
@@ -1416,7 +1416,7 @@ int parse_options(int argc, char **argv) {
for (i = 5; i >= 0; i--) {
// In AirPlay 2 mode, the AP1 name prefix must be
// the same as the AirPlay 2 device id less the colons.
config.ap1_prefix[i] = temporary_airplay_id & 0xFF;
config.ap1_prefix[i] = temporary_airplay_id & 0xFF;
apids[i * 3 + 1] = hexchar[temporary_airplay_id & 0xF];
temporary_airplay_id = temporary_airplay_id >> 4;
apids[i * 3] = hexchar[temporary_airplay_id & 0xF];
@@ -1630,7 +1630,6 @@ void exit_function() {
}
#endif
#ifdef CONFIG_METADATA_HUB
debug(2, "Stopping metadata hub");
metadata_hub_stop();
@@ -2521,7 +2520,6 @@ int main(int argc, char **argv) {
soxr_time_check_thread_started = 1;
#endif
// In AirPlay 2 mode, the AP1 prefix is the same as the device ID less the colons
// In AirPlay 1 mode, the AP1 prefix is calculated by hashing the service name.
#ifndef CONFIG_AIRPLAY_2
@@ -2600,25 +2598,51 @@ int main(int argc, char **argv) {
#endif
#ifdef CONFIG_AIRPLAY_2
ptp_send_control_message_string("T"); // get nqptp to create the named shm interface
int ptp_check_times = 0;
const int ptp_wait_interval_us = 5000;
// wait for up to ten seconds for NQPTP to come online
ptp_send_control_message_string(
"T"); // send this message to get nqptp to create the named shm interface
uint64_t nqptp_start_waiting_time = get_absolute_time_in_ns();
int continue_waiting = 0;
int response = 0;
int64_t time_spent_waiting = 0;
do {
ptp_send_control_message_string("T"); // get nqptp to create the named shm interface
usleep(ptp_wait_interval_us);
ptp_check_times++;
} while ((ptp_shm_interface_open() != 0) &&
(ptp_check_times < (10000000 / ptp_wait_interval_us)));
continue_waiting = 0;
response = ptp_shm_interface_open();
if ((response == -1) && (errno == ENOENT)) {
time_spent_waiting = get_absolute_time_in_ns() - nqptp_start_waiting_time;
if (time_spent_waiting < 10000000000L) {
continue_waiting = 1;
usleep(50000);
}
}
} while (continue_waiting != 0);
if (ptp_shm_interface_open() != 0) {
die("Can't access NQPTP! Is it installed and running?");
} else {
if (ptp_check_times == 1)
debug(1, "NQPTP is online.");
else
debug(1, "NQPTP is online after %u microseconds.", ptp_check_times * ptp_wait_interval_us);
if ((response == -1) && (errno == ENOENT)) {
die("Shairport Sync can not find the nqptp service on this system. Is nqptp installed and "
"running?");
} else if ((response == -1) && (errno == EACCES)) {
die("Shairport Sync must have read access to the nqptp shared memory file in /dev/shm/.");
} else if (response != 0) {
die("an error occurred accessing the nqptp service.");
}
int ptp_clock_version = ptp_get_clock_version();
if (ptp_clock_version == 0) {
die("The nqptp service on this system, which is required for Shairport Sync to operate, does "
"not seem to be initialised.");
} else if (ptp_clock_version < NQPTP_SHM_STRUCTURES_VERSION) {
die("The nqptp service (SMI Version %d) on this system is too old for this version of "
"Shairport Sync, which requires SMI Version %d. Please update.",
ptp_clock_version, NQPTP_SHM_STRUCTURES_VERSION);
} else if (ptp_clock_version > NQPTP_SHM_STRUCTURES_VERSION) {
die("This version of Shairport Sync (SMI Version %d) is too old for the version of nqptp (SMI "
"Version %d) on this system. Please update.",
NQPTP_SHM_STRUCTURES_VERSION, ptp_clock_version);
}
if (time_spent_waiting == 0)
debug(1, "NQPTP is online.");
else
debug(1, "NQPTP came online after %.3f milliseconds.", 0.000001 * time_spent_waiting);
#endif
#ifdef CONFIG_METADATA