feat: implement semaphore locking mechanism for tty devices

application/tom_modem/src/main.c

@@ -157,6 +157,10 @@ int run_op(PROFILE_T *profile,FDS_T *fds)
 }
 static void clean_up()
 {
+    if (unlock_at_port(s_profile.tty_dev))
+    {
+        err_msg("Failed to unlock tty device");
+    }
     if (tcsetattr(s_fds.tty_fd, TCSANOW, &s_fds.old_termios) != 0)
     {
         err_msg("Error restoring old tty attributes");
@@ -174,6 +178,16 @@ int main(int argc, char *argv[])
     FDS_T *fds = &s_fds;
     parse_user_input(argc, argv, profile);
     dump_profile();
+    #ifdef USE_SEMAPHORE
+    if (profile->tty_dev != NULL)
+    {
+        if (lock_at_port(profile->tty_dev))
+        {
+            err_msg("Failed to lock tty device");
+            return COMM_ERROR;
+        }
+    }
+    #endif
     // try open tty devices
     if (tty_open_device(profile,fds))
     {
@@ -184,6 +198,10 @@ int main(int argc, char *argv[])
     if (run_op(profile,fds))
     {
         err_msg("Failed to run operation %d", profile->op);
+        if (unlock_at_port(profile->tty_dev))
+        {
+            err_msg("Failed to unlock tty device");
+        }
         kill(getpid(), SIGINT); 
     }
     

application/tom_modem/src/utils.c

@@ -1,5 +1,48 @@
 #include "utils.h"
 
+#ifdef USE_SEMAPHORE
+void generate_semaphore_name(const char* filename, char* semaphore_name) {
+    snprintf(semaphore_name, MAX_FILENAME_LEN, "%s%s", SEMAPHORE_PREFIX, filename);
+    for (int i = 0; semaphore_name[i] != '\0'; i++) {
+        if (semaphore_name[i] == '/') {
+            semaphore_name[i] = '_';
+        }
+    }
+}
+
+int lock_at_port(char* filename){
+    char semaphore_name[MAX_FILENAME_LEN];
+    generate_semaphore_name(filename, semaphore_name);
+    dbg_msg("semaphore_name: %s", semaphore_name);
+    sem_t *sem = sem_open(semaphore_name, O_CREAT, 0644, 1);
+    if (sem == SEM_FAILED) {
+        perror("sem_open failed");
+        return -1;
+    }
+    wait_start = clock();
+    sem_wait(sem);
+    dbg_msg("waited %f ms for semaphore", wait_total);
+    return 0;
+}
+
+int unlock_at_port(char* filename){
+    char semaphore_name[MAX_FILENAME_LEN];
+    generate_semaphore_name(filename, semaphore_name);
+    dbg_msg("semaphore_name: %s", semaphore_name);
+    sem_t *sem = sem_open(semaphore_name, O_CREAT, 0644, 1);
+    if (sem == SEM_FAILED) {
+        perror("sem_open failed");
+        return -1;
+    }
+    sem_post(sem);
+    sem_close(sem);
+    sem_unlink(semaphore_name);
+    return 0;
+}
+
+#endif
+
+
 static int char_to_hex(char c)
 {
     // convert char to hex

application/tom_modem/src/utils.h

@@ -1,5 +1,6 @@
 #ifndef _UTILS_H
 #define _UTILS_H
+#define USE_SEMAPHORE 1
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
@@ -13,6 +14,22 @@
 #include "extlib/pdu.h"
 #include "time.h"
 
+#ifdef USE_SEMAPHORE
+#include <semaphore.h>
+#include <sys/wait.h>
+#include <sys/types.h>
+#define MAX_FILENAME_LEN 256
+#define SEMAPHORE_PREFIX "tom_modem_lock"
+typedef struct FileLock {
+    char filename[MAX_FILENAME_LEN];
+    sem_t semaphore;
+} FileLock;
+
+void generate_semaphore_name(const char* filename, char* semaphore_name);
+int lock_at_port(char* filename);
+int unlock_at_port(char* filename);
+#endif
+
 extern PROFILE_T s_profile;
 extern FDS_T s_fds;