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diff --git a/filesystem/mounting_and_unmounting.rst b/filesystem/mounting_and_unmounting.rst new file mode 100644 index 0000000..3fd0794 --- /dev/null +++ b/filesystem/mounting_and_unmounting.rst @@ -0,0 +1,102 @@ +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; + }; + +*Node* + The Node is used to produce a linked list of mount table entry nodes. + +*mt_point_node* + 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. + +*mt_fs_root* + 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. + +*options* + XXX + +*fs_info* + 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. + +*pathconf_limits_and_options* + XXX + +*dev* + 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. + |