Added max id for unix_fs_driver + better macros

examples/print_info.c

@@ -53,12 +53,20 @@ main(int argc, char *argv[])
         exit(EXIT_FAILURE);
     }
 
+    UnixFsDriverData driver_data = { path };
+
+    int max_id = unix_fs_driver_get_max_id(&driver_data);
+    if (max_id <= 0) {
+        fprintf(stderr, "Warning: failed to get id of last comment\n");
+    } else if (id >= max_id) {
+        fprintf(stderr, "Last comment has id %d, which is less than %d\n", max_id - 1, id);
+        exit(EXIT_FAILURE);
+    }
+
     CommentHeader *header = malloc(sizeof(CommentHeader));
     header->user_sid = malloc(BUF_SZ);
     header->user_displayname = malloc(BUF_SZ);
 
-    UnixFsDriverData driver_data = { path };
-
     if (driver->get_header(&driver_data, header, id) < 0) {
         fprintf(stderr, "failed to get header of comment, are you sure it exists?\n");
         exit(EXIT_FAILURE);

include/drivers/unix_fs/unix_fs_driver.h

@@ -12,11 +12,12 @@ typedef struct {
 } UnixFsDriverData;
 
 int unix_fs_driver_leave_comment(void *driver_data_ptr, const CommentHeader *header, const char *text);
-
 int unix_fs_driver_get_header(void *driver_data_ptr, CommentHeader *header, int id);
-
 int unix_fs_driver_get_text(void *driver_data_ptr, char *text, int id);
 
 static const Driver unix_fs_driver = { unix_fs_driver_leave_comment, unix_fs_driver_get_header, unix_fs_driver_get_text };
 
+int unix_fs_driver_get_max_id(void *driver_data_ptr);
+
+
 #endif /* UNIX_FS_DRIVER_H */

src/drivers/unix_fs/unix_fs_driver.c

@@ -16,15 +16,22 @@
 
 #define READ_BUF_SZ 256
 
-#define SWRITE(fd, buf, count) \
+#define SWRITE(fd, buf, count) do { \
     if (write(fd, buf, count) < count) { \
         return -EINVAL; \
-    }
+    } \
+} while(0);
 
-#define SREAD(fd, buf, count) \
+#define SREAD(fd, buf, count) do { \
     if (read(fd, buf, count) < count) { \
         return -EINVAL; \
-    }
+    } \
+} while (0);
+
+#define NOLCK_ABORT() do { \
+    fprintf(stderr, "Failed to release id control file, aborting...\n"); \
+    abort(); \
+} while (0);
 
 int
 is_valid_directory(const char *path)
@@ -121,6 +128,43 @@ release_id_ctrl_file(FILE *id_ctrl_file)
     return fclose(id_ctrl_file);
 }
 
+int
+unix_fs_driver_get_max_id(void *driver_data_ptr)
+{
+    char *path, *id_ctrl_file_path;
+    FILE *id_ctrl_file;
+    int retval;
+
+    path = ((UnixFsDriverData*) driver_data_ptr)->path;
+
+    id_ctrl_file_path = NULL;
+    id_ctrl_file = NULL;
+
+    if (asprintf(&id_ctrl_file_path, "%s/%s", path, ID_CTRL_FILE) < 0) {
+        id_ctrl_file_path = NULL;
+        retval = -ENOMEM;
+        goto defer;
+    }
+
+    if (!(id_ctrl_file = acquire_id_ctrl_file(id_ctrl_file_path))) {
+        retval = -EIO;
+        goto defer;
+    }
+    
+    if (fscanf(id_ctrl_file, "%d", &retval) < 1) {
+        retval = -EIO;
+        goto defer;
+    }
+defer:
+    if (id_ctrl_file) {
+        if (release_id_ctrl_file(id_ctrl_file) < 0) {
+            NOLCK_ABORT();
+        }
+    }
+    free(id_ctrl_file_path);
+    return retval;
+}
+
 int
 unix_fs_driver_leave_comment(void *driver_data_ptr, const CommentHeader *header, const char *text)
 {
@@ -196,8 +240,7 @@ unix_fs_driver_leave_comment(void *driver_data_ptr, const CommentHeader *header,
 defer:
     if (id_ctrl_file) {
         if (release_id_ctrl_file(id_ctrl_file) < 0) {
-            fprintf(stderr, "Failed to release id control file, aborting...\n");
+            NOLCK_ABORT();
-            abort();
         }
     }
     free(id_ctrl_file_path);