path: root/filesystem/mounting_and_unmounting.rst
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authorAmar Takhar <>2016-01-16 10:28:13 -0500
committerAmar Takhar <>2016-05-02 20:51:22 -0400
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+Mounting and Unmounting Filesystems
+Mount Points
+The following is the list of the characteristics of a mount point:
+- The mount point must be a directory. It may have files and other
+ directories under it. These files and directories will be hidden when the
+ filesystem is mounted.
+- The task must have read/write/execute permissions to the mount point
+ or the mount attempt will be rejected.
+- Only one filesystem can be mounted to a single mount point.
+- The Root of the mountable filesystem will be referenced by the name
+ of the mount point after the mount is complete.
+Mount Table Chain
+The mount table chain is a dynamic list of structures that describe
+mounted filesystems a specific points in the filesystem hierarchy. It is
+initialized to an empty state during the base filesystem initialization.
+The mount operation will add entries to the mount table chain. The
+un-mount operation will remove entries from the mount table chain.
+Each entry in the mount table chain is of the following type:
+.. code:: c
+ struct rtems_filesystem_mount_table_entry_tt
+ {
+ Chain_Node Node;
+ rtems_filesystem_location_info_t mt_point_node;
+ rtems_filesystem_location_info_t mt_fs_root;
+ int options;
+ void \*fs_info;
+ rtems_filesystem_limits_and_options_t pathconf_limits_and_options;
+ /*
+ * When someone adds a mounted filesystem on a real device,
+ * this will need to be used.
+ *
+ * The best option long term for this is probably an
+ * open file descriptor.
+ \*/
+ char \*dev;
+ };
+ The Node is used to produce a linked list of mount table entry nodes.
+ The mt_point_node contains all information necessary to access the
+ directory where a filesystem is mounted onto. This element may contain
+ memory that is allocated during a path evaluation of the filesystem
+ containing the mountpoint directory. The generic code allows this
+ memory to be returned by unmount when the filesystem identified by
+ mt_fs_root is unmounted.
+ The mt_fs_root contains all information necessary to identify the root
+ of the mounted filesystem. The user is never allowed access to this
+ node by the generic code, but it is used to identify to the mounted
+ filesystem where to start evaluation of pathnames at.
+ The fs_info element is a location available for use by the mounted file
+ system to identify unique things applicable to this instance of the file
+ system. For example the IMFS uses this space to provide node
+ identification that is unique for each instance (mounting) of the filesystem.
+ This character string represents the device where the filesystem will reside.
+Adding entries to the chain during mount
+When a filesystem is mounted, its presence and location in the file
+system hierarchy is recorded in a dynamic list structure known as a chain.
+A unique rtems_filesystem_mount_table_entry_tt structure is logged for
+each filesystem that is mounted. This includes the base filesystem.
+Removing entries from the chain during unmount
+When a filesystem is dismounted its entry in the mount table chain is
+extracted and the memory for this entry is freed.
+.. COMMENT: COPYRIGHT (c) 1988-2002.
+.. COMMENT: On-Line Applications Research Corporation (OAR).
+.. COMMENT: All rights reserved.