* Spaces to tabs.
* Carriage returns to simple new lines. git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@21627 a95241bf-73f2-0310-859d-f6bbb57e9c96
This commit is contained in:
Axel Dörfler
parent
ec9f5ea799
commit
ca210f74f1
File diff suppressed because it is too large
Load Diff
@ -3,210 +3,210 @@
|
||||
* Distributed under the terms of the MIT License.
|
||||
*
|
||||
* Authors:
|
||||
* Ingo Weinhold
|
||||
* Ingo Weinhold
|
||||
*/
|
||||
|
||||
|
||||
/*!
|
||||
\page fs_modules File System Modules
|
||||
\page fs_modules File System Modules
|
||||
|
||||
To support a particular file system (FS), a kernel module implementing a
|
||||
special interface (\c file_system_module_info defined in \c <fs_interface.h>)
|
||||
has to be provided. As for any other module the \c std_ops() hook is invoked
|
||||
with \c B_MODULE_INIT directly after the FS module has been loaded by the
|
||||
kernel, and with \c B_MODULE_UNINIT before it is unloaded, thus providing
|
||||
a simple mechanism for one-time module initializations. The same module is
|
||||
used for accessing any volume of that FS type.
|
||||
To support a particular file system (FS), a kernel module implementing a
|
||||
special interface (\c file_system_module_info defined in \c <fs_interface.h>)
|
||||
has to be provided. As for any other module the \c std_ops() hook is invoked
|
||||
with \c B_MODULE_INIT directly after the FS module has been loaded by the
|
||||
kernel, and with \c B_MODULE_UNINIT before it is unloaded, thus providing
|
||||
a simple mechanism for one-time module initializations. The same module is
|
||||
used for accessing any volume of that FS type.
|
||||
|
||||
|
||||
\section objects File System Objects
|
||||
\section objects File System Objects
|
||||
|
||||
There are several types of objects a FS module has to deal with directly or
|
||||
indirectly:
|
||||
There are several types of objects a FS module has to deal with directly or
|
||||
indirectly:
|
||||
|
||||
- A \em volume is an instance of a file system. For a disk-based file
|
||||
system it corresponds to a disk, partition, or disk image file. When
|
||||
mounting a volume the virtual file system layer (VFS) assigns a unique
|
||||
number (ID, of type \c mount_id aka \c dev_t) to it and a handle (type
|
||||
\c fs_volume, in fact \c void*) provided by
|
||||
the file system. Whenever the FS requests a volume-related service from the
|
||||
kernel, it has to pass the volume ID, and whenever the VFS asks the FS to
|
||||
perform an operation, it supplies the handle. Normally the handle is a
|
||||
pointer to a data structure the FS allocates to associate data with the
|
||||
volume.
|
||||
- A \em volume is an instance of a file system. For a disk-based file
|
||||
system it corresponds to a disk, partition, or disk image file. When
|
||||
mounting a volume the virtual file system layer (VFS) assigns a unique
|
||||
number (ID, of type \c mount_id aka \c dev_t) to it and a handle (type
|
||||
\c fs_volume, in fact \c void*) provided by
|
||||
the file system. Whenever the FS requests a volume-related service from the
|
||||
kernel, it has to pass the volume ID, and whenever the VFS asks the FS to
|
||||
perform an operation, it supplies the handle. Normally the handle is a
|
||||
pointer to a data structure the FS allocates to associate data with the
|
||||
volume.
|
||||
|
||||
- A \em node is contained by a volume. It can be of type file, directory, or
|
||||
symbolic link (symlink). Just as volumes nodes are associated with an ID
|
||||
(type \c vnode_id aka ino_t) and, if in use, also with a handle
|
||||
(type \c fs_vnode, in fact \c void*).
|
||||
Unlike the volume ID the node ID is defined by the FS. It often
|
||||
has a meaning to the FS, e.g. file systems using inodes might choose the
|
||||
inode number corresponding to the node. As long as the volume is mounted
|
||||
and the node is known to the VFS, its node ID must not change. The node
|
||||
handle is again a pointer to a data structure allocated by the FS.
|
||||
|
||||
- A \em vnode (VFS node) is the VFS representation of a node. A volume may
|
||||
contain a great number of nodes, but at a time only a few are represented
|
||||
by vnodes, usually only those that are currently in use (sometimes a few
|
||||
more).
|
||||
- A \em node is contained by a volume. It can be of type file, directory, or
|
||||
symbolic link (symlink). Just as volumes nodes are associated with an ID
|
||||
(type \c vnode_id aka ino_t) and, if in use, also with a handle
|
||||
(type \c fs_vnode, in fact \c void*).
|
||||
Unlike the volume ID the node ID is defined by the FS. It often
|
||||
has a meaning to the FS, e.g. file systems using inodes might choose the
|
||||
inode number corresponding to the node. As long as the volume is mounted
|
||||
and the node is known to the VFS, its node ID must not change. The node
|
||||
handle is again a pointer to a data structure allocated by the FS.
|
||||
|
||||
- An \em entry (directory entry) belongs to a directory, has a name, and
|
||||
refers to a node. It is important to understand the difference between
|
||||
entries and nodes: A node doesn't have a name, only the entries that refer
|
||||
to it have. If a FS supports to have more than one entry refer to a single
|
||||
node, it is also said to support "hard links". It is possible that no entry
|
||||
refers to a node. This happens when a node (e.g. a file) is still open, but
|
||||
the last entry referring to it has been removed (the node will be deleted
|
||||
when the it is closed). While entries are to be understood as independent
|
||||
entities, the FS interface does not use IDs or handles to refer to them;
|
||||
it always uses directory and entry name pairs to do that.
|
||||
- A \em vnode (VFS node) is the VFS representation of a node. A volume may
|
||||
contain a great number of nodes, but at a time only a few are represented
|
||||
by vnodes, usually only those that are currently in use (sometimes a few
|
||||
more).
|
||||
|
||||
- An \em attribute is a named and typed data container belonging to a node. A
|
||||
node may have any number of attributes; they are organized in a (virtual or
|
||||
actually existing) attribute directory, through which one can iterate.
|
||||
- An \em entry (directory entry) belongs to a directory, has a name, and
|
||||
refers to a node. It is important to understand the difference between
|
||||
entries and nodes: A node doesn't have a name, only the entries that refer
|
||||
to it have. If a FS supports to have more than one entry refer to a single
|
||||
node, it is also said to support "hard links". It is possible that no entry
|
||||
refers to a node. This happens when a node (e.g. a file) is still open, but
|
||||
the last entry referring to it has been removed (the node will be deleted
|
||||
when the it is closed). While entries are to be understood as independent
|
||||
entities, the FS interface does not use IDs or handles to refer to them;
|
||||
it always uses directory and entry name pairs to do that.
|
||||
|
||||
- An \em index is supposed to provide fast searching capabilities for
|
||||
attributes with a certain name. A volume's index directory allows for
|
||||
iterating through the indices.
|
||||
- An \em attribute is a named and typed data container belonging to a node. A
|
||||
node may have any number of attributes; they are organized in a (virtual or
|
||||
actually existing) attribute directory, through which one can iterate.
|
||||
|
||||
- A \em query is a fully virtual object for searching for entries via an
|
||||
expression matching entry name, node size, node modification date, and/or
|
||||
node attributes. The mechanism of retrieving the entries found by a query
|
||||
is similar to that for reading a directory contents. A query can be live
|
||||
in which case the creator of the query is notified by the FS whenever an
|
||||
entry no longer matches the query expression or starts matching.
|
||||
- An \em index is supposed to provide fast searching capabilities for
|
||||
attributes with a certain name. A volume's index directory allows for
|
||||
iterating through the indices.
|
||||
|
||||
- A \em query is a fully virtual object for searching for entries via an
|
||||
expression matching entry name, node size, node modification date, and/or
|
||||
node attributes. The mechanism of retrieving the entries found by a query
|
||||
is similar to that for reading a directory contents. A query can be live
|
||||
in which case the creator of the query is notified by the FS whenever an
|
||||
entry no longer matches the query expression or starts matching.
|
||||
|
||||
|
||||
\section concepts Generic Concepts
|
||||
\section concepts Generic Concepts
|
||||
|
||||
A FS module has to (or can) provide quite a lot of hook functions. There are
|
||||
a few concepts that apply to several groups of them:
|
||||
A FS module has to (or can) provide quite a lot of hook functions. There are
|
||||
a few concepts that apply to several groups of them:
|
||||
|
||||
- <em>Opening, Closing, and Cookies</em>: Many FS objects can be opened and
|
||||
closed, namely nodes in general, directories, attribute directories,
|
||||
attributes, the index directory, and queries. In each case there are three
|
||||
hook functions: <tt>open*()</tt>, <tt>close*()</tt>, and
|
||||
<tt>free*_cookie()</tt>. The <tt>open*()</tt> hook is passed all that is
|
||||
needed to identify the object to be opened and, in some cases, additional
|
||||
parameters e.g. specifying a particular opening mode. The implementation
|
||||
is required to return a cookie (type \c fs_cookie, in fact \c void*),
|
||||
usually a pointer to a data structure the FS allocates. In some cases (e.g.
|
||||
when an iteration state is associated with the cookie) a new cookie must
|
||||
be allocated for each instance of opening the object. The cookie is passed
|
||||
to all hooks that operate on a thusly opened object. The <tt>close*()</tt>
|
||||
hook is invoked to signal that the cookie is to be closed. At this point
|
||||
the cookie might still be in use. Blocking FS hooks (e.g. blocking
|
||||
read/write operations) using the same cookie have to be unblocked. When
|
||||
the cookie stops being in use the <tt>free*_cookie()</tt> hook is called;
|
||||
it has to free the cookie.
|
||||
- <em>Opening, Closing, and Cookies</em>: Many FS objects can be opened and
|
||||
closed, namely nodes in general, directories, attribute directories,
|
||||
attributes, the index directory, and queries. In each case there are three
|
||||
hook functions: <tt>open*()</tt>, <tt>close*()</tt>, and
|
||||
<tt>free*_cookie()</tt>. The <tt>open*()</tt> hook is passed all that is
|
||||
needed to identify the object to be opened and, in some cases, additional
|
||||
parameters e.g. specifying a particular opening mode. The implementation
|
||||
is required to return a cookie (type \c fs_cookie, in fact \c void*),
|
||||
usually a pointer to a data structure the FS allocates. In some cases (e.g.
|
||||
when an iteration state is associated with the cookie) a new cookie must
|
||||
be allocated for each instance of opening the object. The cookie is passed
|
||||
to all hooks that operate on a thusly opened object. The <tt>close*()</tt>
|
||||
hook is invoked to signal that the cookie is to be closed. At this point
|
||||
the cookie might still be in use. Blocking FS hooks (e.g. blocking
|
||||
read/write operations) using the same cookie have to be unblocked. When
|
||||
the cookie stops being in use the <tt>free*_cookie()</tt> hook is called;
|
||||
it has to free the cookie.
|
||||
|
||||
- <em>Entry Iteration</em>: For the FS objects serving as containers for
|
||||
other objects, i.e. directories, attribute directories, the index
|
||||
directory, and queries, the cookie mechanism is used for a stateful
|
||||
iteration through the contained objects. The <tt>read_*()</tt> hook reads
|
||||
the next one or more entries into a <tt>struct dirent</tt> buffer. The
|
||||
<tt>rewind_*()</tt> hook resets the iteration state to the first entry.
|
||||
- <em>Entry Iteration</em>: For the FS objects serving as containers for
|
||||
other objects, i.e. directories, attribute directories, the index
|
||||
directory, and queries, the cookie mechanism is used for a stateful
|
||||
iteration through the contained objects. The <tt>read_*()</tt> hook reads
|
||||
the next one or more entries into a <tt>struct dirent</tt> buffer. The
|
||||
<tt>rewind_*()</tt> hook resets the iteration state to the first entry.
|
||||
|
||||
- <em>Stat Information</em>: In case of nodes, attributes, and indices
|
||||
detailed information about an object are requested via a
|
||||
<tt>read*_stat()</tt> hook and must be written into a <tt>struct stat</tt>
|
||||
buffer.
|
||||
- <em>Stat Information</em>: In case of nodes, attributes, and indices
|
||||
detailed information about an object are requested via a
|
||||
<tt>read*_stat()</tt> hook and must be written into a <tt>struct stat</tt>
|
||||
buffer.
|
||||
|
||||
|
||||
\section vnodes VNodes
|
||||
\section vnodes VNodes
|
||||
|
||||
A vnode is the VFS representation of a node. As soon as an access to a node
|
||||
is requested, the VFS creates a corresponding vnode. The requesting entity
|
||||
gets a reference to the vnode for the time it works with the vnode and
|
||||
releases the reference when done. When the last reference to a vnode has been
|
||||
surrendered, the vnode is unused and the VFS can decide to destroy it
|
||||
(usually it is cached for a while longer).
|
||||
A vnode is the VFS representation of a node. As soon as an access to a node
|
||||
is requested, the VFS creates a corresponding vnode. The requesting entity
|
||||
gets a reference to the vnode for the time it works with the vnode and
|
||||
releases the reference when done. When the last reference to a vnode has been
|
||||
surrendered, the vnode is unused and the VFS can decide to destroy it
|
||||
(usually it is cached for a while longer).
|
||||
|
||||
When the VFS creates a vnode, it invokes the FS's
|
||||
\link file_system_module_info::get_vnode get_vnode() \endlink
|
||||
hook to let it create the respective node handle (unless the FS requests the
|
||||
creation of the vnode explicitely by calling publish_vnode()). That's the
|
||||
only hook that specifies a node by ID; to all other node-related hooks the
|
||||
node handle is passed. When the VFS deletes the vnode, it invokes the FS's
|
||||
\link file_system_module_info::put_vnode put_vnode() \endlink
|
||||
hook or, if the node was marked removed,
|
||||
\link file_system_module_info::remove_vnode remove_vnode() \endlink.
|
||||
When the VFS creates a vnode, it invokes the FS's
|
||||
\link file_system_module_info::get_vnode get_vnode() \endlink
|
||||
hook to let it create the respective node handle (unless the FS requests the
|
||||
creation of the vnode explicitely by calling publish_vnode()). That's the
|
||||
only hook that specifies a node by ID; to all other node-related hooks the
|
||||
node handle is passed. When the VFS deletes the vnode, it invokes the FS's
|
||||
\link file_system_module_info::put_vnode put_vnode() \endlink
|
||||
hook or, if the node was marked removed,
|
||||
\link file_system_module_info::remove_vnode remove_vnode() \endlink.
|
||||
|
||||
There are only four FS hooks through which the VFS gains knowledge of the
|
||||
existence of a node. The first one is the
|
||||
\link file_system_module_info::mount mount() \endlink
|
||||
hook. It is supposed to call \c publish_vnode() for the root node of the
|
||||
volume and return its ID. The second one is the
|
||||
\link file_system_module_info::lookup lookup() \endlink
|
||||
hook. Given a node handle of a directory and an entry name, it is supposed to
|
||||
call \c get_vnode() for the node the entry refers to and return the node ID.
|
||||
The remaining two hooks,
|
||||
\link file_system_module_info::read_dir read_dir() \endlink and
|
||||
\link file_system_module_info::read_query read_query() \endlink,
|
||||
both return entries in a <tt>struct dirent</tt> structure, which also
|
||||
contains the ID of the node the entry refers to.
|
||||
There are only four FS hooks through which the VFS gains knowledge of the
|
||||
existence of a node. The first one is the
|
||||
\link file_system_module_info::mount mount() \endlink
|
||||
hook. It is supposed to call \c publish_vnode() for the root node of the
|
||||
volume and return its ID. The second one is the
|
||||
\link file_system_module_info::lookup lookup() \endlink
|
||||
hook. Given a node handle of a directory and an entry name, it is supposed to
|
||||
call \c get_vnode() for the node the entry refers to and return the node ID.
|
||||
The remaining two hooks,
|
||||
\link file_system_module_info::read_dir read_dir() \endlink and
|
||||
\link file_system_module_info::read_query read_query() \endlink,
|
||||
both return entries in a <tt>struct dirent</tt> structure, which also
|
||||
contains the ID of the node the entry refers to.
|
||||
|
||||
|
||||
\section mandatory_hooks Mandatory Hooks
|
||||
\section mandatory_hooks Mandatory Hooks
|
||||
|
||||
Which hooks a FS module should provide mainly depends on what functionality
|
||||
it features. E.g. a FS without support for attribute, indices, and/or queries
|
||||
can omit the respective hooks (i.e. set them to \c NULL in the module
|
||||
structure). Some hooks are mandatory, though. A minimal read-only FS module
|
||||
must implement:
|
||||
Which hooks a FS module should provide mainly depends on what functionality
|
||||
it features. E.g. a FS without support for attribute, indices, and/or queries
|
||||
can omit the respective hooks (i.e. set them to \c NULL in the module
|
||||
structure). Some hooks are mandatory, though. A minimal read-only FS module
|
||||
must implement:
|
||||
|
||||
- \link file_system_module_info::mount mount() \endlink and
|
||||
\link file_system_module_info::unmount unmount() \endlink:
|
||||
Mounting and unmounting a volume is required for pretty obvious reasons.
|
||||
- \link file_system_module_info::mount mount() \endlink and
|
||||
\link file_system_module_info::unmount unmount() \endlink:
|
||||
Mounting and unmounting a volume is required for pretty obvious reasons.
|
||||
|
||||
- \link file_system_module_info::lookup lookup() \endlink:
|
||||
The VFS uses this hook to resolve path names. It is probably one of the
|
||||
most frequently invoked hooks.
|
||||
- \link file_system_module_info::lookup lookup() \endlink:
|
||||
The VFS uses this hook to resolve path names. It is probably one of the
|
||||
most frequently invoked hooks.
|
||||
|
||||
- \link file_system_module_info::get_vnode get_vnode() \endlink and
|
||||
\link file_system_module_info::put_vnode put_vnode() \endlink:
|
||||
Create respectively destroy the FS's private node handle when
|
||||
the VFS creates/deletes the vnode for a particular node.
|
||||
- \link file_system_module_info::get_vnode get_vnode() \endlink and
|
||||
\link file_system_module_info::put_vnode put_vnode() \endlink:
|
||||
Create respectively destroy the FS's private node handle when
|
||||
the VFS creates/deletes the vnode for a particular node.
|
||||
|
||||
- \link file_system_module_info::read_stat read_stat() \endlink:
|
||||
Return a <tt>struct stat</tt> info for the given node, consisting of the
|
||||
type and size of the node, its owner and access permissions, as well as
|
||||
certain access times.
|
||||
- \link file_system_module_info::read_stat read_stat() \endlink:
|
||||
Return a <tt>struct stat</tt> info for the given node, consisting of the
|
||||
type and size of the node, its owner and access permissions, as well as
|
||||
certain access times.
|
||||
|
||||
- \link file_system_module_info::open open() \endlink,
|
||||
\link file_system_module_info::close close() \endlink, and
|
||||
\link file_system_module_info::free_cookie free_cookie() \endlink:
|
||||
Open and close a node as explained in \ref concepts.
|
||||
- \link file_system_module_info::open open() \endlink,
|
||||
\link file_system_module_info::close close() \endlink, and
|
||||
\link file_system_module_info::free_cookie free_cookie() \endlink:
|
||||
Open and close a node as explained in \ref concepts.
|
||||
|
||||
- \link file_system_module_info::read read() \endlink:
|
||||
Read data from an opened node (file). Even if the FS does not feature
|
||||
files, the hook has to be present anyway; it should return an error in this
|
||||
case.
|
||||
- \link file_system_module_info::read read() \endlink:
|
||||
Read data from an opened node (file). Even if the FS does not feature
|
||||
files, the hook has to be present anyway; it should return an error in this
|
||||
case.
|
||||
|
||||
- \link file_system_module_info::open_dir open_dir() \endlink,
|
||||
\link file_system_module_info::close_dir close_dir() \endlink, and
|
||||
\link file_system_module_info::free_dir_cookie free_dir_cookie() \endlink:
|
||||
Open and close a directory for entry iteration as explained in
|
||||
\ref concepts.
|
||||
- \link file_system_module_info::open_dir open_dir() \endlink,
|
||||
\link file_system_module_info::close_dir close_dir() \endlink, and
|
||||
\link file_system_module_info::free_dir_cookie free_dir_cookie() \endlink:
|
||||
Open and close a directory for entry iteration as explained in
|
||||
\ref concepts.
|
||||
|
||||
- \link file_system_module_info::read_dir read_dir() \endlink and
|
||||
\link file_system_module_info::rewind_dir rewind_dir() \endlink:
|
||||
Read the next entry/entries from a directory, respectively reset the
|
||||
iterator to the first entry, as explained in \ref concepts.
|
||||
- \link file_system_module_info::read_dir read_dir() \endlink and
|
||||
\link file_system_module_info::rewind_dir rewind_dir() \endlink:
|
||||
Read the next entry/entries from a directory, respectively reset the
|
||||
iterator to the first entry, as explained in \ref concepts.
|
||||
|
||||
Although not strictly mandatory, a FS should additionally implement the
|
||||
following hooks:
|
||||
Although not strictly mandatory, a FS should additionally implement the
|
||||
following hooks:
|
||||
|
||||
- \link file_system_module_info::read_fs_info read_fs_info() \endlink:
|
||||
Return general information about the volume, e.g. total and free size, and
|
||||
what special features (attributes, MIME types, queries) the volume/FS
|
||||
supports.
|
||||
- \link file_system_module_info::read_fs_info read_fs_info() \endlink:
|
||||
Return general information about the volume, e.g. total and free size, and
|
||||
what special features (attributes, MIME types, queries) the volume/FS
|
||||
supports.
|
||||
|
||||
- \link file_system_module_info::read_symlink read_symlink() \endlink:
|
||||
Read the value of a symbolic link. Needed only, if the FS and volume
|
||||
support symbolic links at all. If absent symbolic links stored on the
|
||||
volume won't be interpreted.
|
||||
- \link file_system_module_info::read_symlink read_symlink() \endlink:
|
||||
Read the value of a symbolic link. Needed only, if the FS and volume
|
||||
support symbolic links at all. If absent symbolic links stored on the
|
||||
volume won't be interpreted.
|
||||
|
||||
- \link file_system_module_info::access access() \endlink:
|
||||
Return whether the current user has the given access permissions for a
|
||||
node. If the hook is absent the user is considerd to have all permissions.
|
||||
- \link file_system_module_info::access access() \endlink:
|
||||
Return whether the current user has the given access permissions for a
|
||||
node. If the hook is absent the user is considerd to have all permissions.
|
||||
*/
|
||||
|
||||
Loading…
Reference in New Issue
Block a user