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102 lines
3.7 KiB
ReStructuredText
102 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-SA-4.0
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.. Copyright (C) 1988, 2002 On-Line Applications Research Corporation (OAR)
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Mounting and Unmounting Filesystems
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***********************************
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Mount Points
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============
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The following is the list of the characteristics of a mount point:
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- The mount point must be a directory. It may have files and other directories
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under it. These files and directories will be hidden when the filesystem is
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mounted.
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- The task must have read/write/execute permissions to the mount point or the
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mount attempt will be rejected.
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- Only one filesystem can be mounted to a single mount point.
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- The Root of the mountable filesystem will be referenced by the name of the
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mount point after the mount is complete.
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Mount Table Chain
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=================
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The mount table chain is a dynamic list of structures that describe mounted
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filesystems a specific points in the filesystem hierarchy. It is initialized to
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an empty state during the base filesystem initialization. The mount operation
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will add entries to the mount table chain. The un-mount operation will remove
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entries from the mount table chain.
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Each entry in the mount table chain is of the following type:
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.. code-block:: c
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struct rtems_filesystem_mount_table_entry_tt
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{
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Chain_Node Node;
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rtems_filesystem_location_info_t mt_point_node;
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rtems_filesystem_location_info_t mt_fs_root;
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int options;
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void *fs_info;
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rtems_filesystem_limits_and_options_t pathconf_limits_and_options;
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/*
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* When someone adds a mounted filesystem on a real device,
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* this will need to be used.
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*
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* The best option long term for this is probably an
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* open file descriptor.
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*/
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char *dev;
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};
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*Node*
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The Node is used to produce a linked list of mount table entry nodes.
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*mt_point_node*
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The mt_point_node contains all information necessary to access the
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directory where a filesystem is mounted onto. This element may contain
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memory that is allocated during a path evaluation of the filesystem
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containing the mountpoint directory. The generic code allows this memory
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to be returned by unmount when the filesystem identified by mt_fs_root is
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unmounted.
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*mt_fs_root*
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The mt_fs_root contains all information necessary to identify the root of
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the mounted filesystem. The user is never allowed access to this node by
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the generic code, but it is used to identify to the mounted filesystem
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where to start evaluation of pathnames at.
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*options*
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XXX
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*fs_info*
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The fs_info element is a location available for use by the mounted file
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system to identify unique things applicable to this instance of the file
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system. For example the IMFS uses this space to provide node
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identification that is unique for each instance (mounting) of the
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filesystem.
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*pathconf_limits_and_options*
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XXX
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*dev*
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This character string represents the device where the filesystem will reside.
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Adding entries to the chain during mount
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========================================
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When a filesystem is mounted, its presence and location in the file system
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hierarchy is recorded in a dynamic list structure known as a chain. A unique
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rtems_filesystem_mount_table_entry_tt structure is logged for each filesystem
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that is mounted. This includes the base filesystem.
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Removing entries from the chain during unmount
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==============================================
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When a filesystem is dismounted its entry in the mount table chain is extracted
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and the memory for this entry is freed.
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