vfs: add format function in vfs api

sys/include/vfs.h

@@ -426,6 +426,16 @@ struct vfs_dir_ops {
  * Similar, but not equal, to struct super_operations in Linux
  */
 struct vfs_file_system_ops {
+    /**
+     * @brief Format the file system on the given mount point
+     *
+     * @param[in]   mountp  file system to format
+     *
+     * @return 0 on success
+     * @return <0 on error
+     */
+    int (*format) (vfs_mount_t *mountp);
+
     /**
      * @brief Perform any extra processing needed after mounting a file system
      *
@@ -695,6 +705,21 @@ int vfs_readdir(vfs_DIR *dirp, vfs_dirent_t *entry);
  */
 int vfs_closedir(vfs_DIR *dirp);
 
+/**
+ * @brief Format a file system
+ *
+ * @p mountp should have been populated in advance with a file system driver,
+ * a mount point, and private_data (if the file system driver uses one).
+ *
+ * @pre @p mountp must not be mounted
+ *
+ * @param[in]  mountp   pointer to the mount structure of the filesystem to format
+ *
+ * @return 0 on success
+ * @return <0 on error
+ */
+int vfs_format(vfs_mount_t *mountp);
+
 /**
  * @brief Mount a file system
  *

sys/vfs/vfs.c

@@ -407,9 +407,18 @@ int vfs_closedir(vfs_DIR *dirp)
     return res;
 }
 
-int vfs_mount(vfs_mount_t *mountp)
+/**
+ * @brief Check if the given mount point is mounted
+ *
+ * If the mount point is not mounted, _mount_mutex will be locked by this function
+ *
+ * @param mountp    mount point to check
+ * @return 0 on success (mount point is valid and not mounted)
+ * @return -EINVAL if mountp is invalid
+ * @return -EBUSY if mountp is already mounted
+ */
+static int check_mount(vfs_mount_t *mountp)
 {
-    DEBUG("vfs_mount: %p\n", (void *)mountp);
     if ((mountp == NULL) || (mountp->fs == NULL) || (mountp->mount_point == NULL)) {
         return -EINVAL;
     }
@@ -429,11 +438,43 @@ int vfs_mount(vfs_mount_t *mountp)
         DEBUG("vfs_mount: Already mounted\n");
         return -EBUSY;
     }
+
+    return 0;
+}
+
+int vfs_format(vfs_mount_t *mountp)
+{
+    DEBUG("vfs_format: %p\n", (void *)mountp);
+    int ret = check_mount(mountp);
+    if (ret < 0) {
+        return ret;
+    }
+    mutex_unlock(&_mount_mutex);
+
+    if (mountp->fs->fs_op != NULL) {
+        if (mountp->fs->fs_op->format != NULL) {
+            return mountp->fs->fs_op->format(mountp);
+        }
+    }
+
+    /* Format operation not supported */
+    return -ENOTSUP;
+}
+
+int vfs_mount(vfs_mount_t *mountp)
+{
+    DEBUG("vfs_mount: %p\n", (void *)mountp);
+    int ret = check_mount(mountp);
+    if (ret < 0) {
+        return ret;
+    }
+
     if (mountp->fs->fs_op != NULL) {
         if (mountp->fs->fs_op->mount != NULL) {
             /* yes, a file system driver does not need to implement mount/umount */
             int res = mountp->fs->fs_op->mount(mountp);
             if (res < 0) {
+                DEBUG("vfs_mount: error %d\n", res);
                 mutex_unlock(&_mount_mutex);
                 return res;
             }