Add uc_restart_counter concept

src/restart_counter.c

@@ -0,0 +1,100 @@
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include "ucore/restart_counter.h"
+
+static UCRCResult uc_restart_counter_lock(int fd)
+{
+    int rc = lockf(fd, F_TLOCK, 0);
+
+    if (rc == -1 && (errno == EACCES || errno == EAGAIN)) {
+        return UC_RC_ERR_FILE_LOCKED; 
+    } else if (rc == -1) {
+        return UC_RC_ERR_UNSPECIFIED;
+    }
+
+    return UC_RC_OK;
+}
+
+UCRCResult uc_restart_counter_init(
+                                   struct UCRestartCounter *counter, 
+                                   const char *filename,
+                                   unsigned int flags)
+{
+    int fd;
+    UCRCResult rc = UC_RC_OK;
+    char buf[64];
+    ssize_t n;
+
+    counter->counter = 0;
+    counter->fd = -1;
+
+    fd = open(filename, O_CREAT|O_RDWR, 0600);
+
+    if (fd == -1) {
+        return UC_RC_ERR_FILE_ACCESS_ERROR;
+    }
+    if (flags & UC_RC_FL_LOCK_FILE) {
+        rc = uc_restart_counter_lock(fd);
+        if (rc != UC_RC_OK) {
+            close(fd);
+            return rc;
+        }
+        counter->fd = fd;
+    }
+
+    buf[0] = 0;
+    n = read(fd, buf, sizeof buf - 1);
+    if (n > 0) {
+        buf[n] = 0;
+        if (sscanf(buf, "%u", &counter->counter) == 1) {
+            counter->counter++;
+            rc = UC_RC_OK;
+        } else {
+            rc = UC_RC_ERR_FILE_CONTENT_ERROR;
+        }
+
+
+        if (lseek(fd, 0, SEEK_SET) != 0 ||
+            ftruncate(fd,0) != 0) {
+            rc = UC_RC_ERR_UNSPECIFIED;
+        }
+
+
+    } else if (n < 0) {
+        rc = UC_RC_ERR_FILE_ACCESS_ERROR;
+    } //if n is 0, we act as we created the file for the 1. time
+
+    snprintf(buf, sizeof buf, "%u\n", counter->counter);
+    n = strlen(buf);
+    if (write(fd, buf, n) != n) {
+        rc = UC_RC_ERR_UNSPECIFIED;
+    }
+    
+    if ((flags & UC_RC_FL_LOCK_FILE) == 0) {
+        close(fd);
+    }
+
+    return rc;
+}
+
+UCRCResult uc_restart_counter_close(struct UCRestartCounter *counter)
+{
+    if (counter->fd < 0) {
+        return UC_RC_ERR_NOT_OPENED;
+    }
+
+    close(counter->fd); //also releases the lock
+    counter->fd = -1;
+
+    return UC_RC_OK;
+}
+
+unsigned int uc_restart_counter_get(const struct UCRestartCounter *counter)
+{
+    return counter->counter;
+}