haiku/docs/user/storage/Node.dox

/*
 * Copyright 2002-2011 Haiku Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Tyler Dauwalder, tylerdauwalder@users.sf.net
 *		John Scipione, jscipione@gmail.com
 *		Ingo Weinhold, bonefish@users.sf.net
 *
 * Corresponds to:
 *		headers/os/app/Node.h	rev 42803
 *		src/kits/app/Node.cpp	rev 42803
 */


/*!
	\file Node.h
	\ingroup storage
	\ingroup libbe
	\brief Provides the BNode class and node_ref structure.
*/


/*!
	\struct node_ref
	\ingroup storage
	\ingroup libbe
	\brief Reference structure to a particular vnode on a device.
*/


/*!
	\fn node_ref::node_ref()
	\brief Creates an uninitialized node_ref object.
*/


/*!
	\fn node_ref::node_ref(const node_ref &ref)
	\brief Creates a copy of the given node_ref object.

	\param ref the node_ref to be copied.
*/


/*!
	\fn bool node_ref::operator==(const node_ref &ref) const
	\brief Tests whether this node_ref and the supplied one are equal.

	\param ref the node_ref to be compared with.

	\return \c true, if the objects are equal, \c false otherwise.
*/


/*!
	\fn bool node_ref::operator!=(const node_ref &ref) const
	\brief Tests whether this node_ref and the supplied one are not equal.

	\param ref the node_ref to be compared with.

	\return \c true, if the objects are \b not equal, \c false otherwise.
*/


/*!
	\fn node_ref& node_ref::operator=(const node_ref &ref)
	\brief Makes this node ref a copy of the supplied one.

	\param ref the node_ref to be copied.

	\return a reference to this object.
*/


/*!
	\class BNode
	\ingroup storage
	\ingroup libbe
	\brief A BNode represents a chunk of data in the filesystem.

	The BNode class provides an interface for manipulating the data and
	attributes belonging to filesystem entries. The BNode is unaware of the
	name that refers to it in the filesystem (i.e. its entry), instead, a
	BNode is concerned solely with the entry's data and attributes.
*/


/*!
	\var BNode::fFd

	File descriptor for the given node.
*/


/*!
	\var BNode::fAttrFd

	File descriptor for the attribute directory of the node.
	Initialized lazily.
*/


/*!
	\var BNode::fCStatus

	The object's initialization status.
*/


/*!
	\fn BNode::BNode()
	\brief Creates an uninitialized BNode object.
*/


/*!
	\fn BNode::BNode(const entry_ref *ref)
	\brief Creates a BNode object and initializes it to the specified
		entry_ref.

	\param ref the entry_ref referring to the entry.
*/


/*!
	\fn BNode::BNode(const BEntry *entry)
	\brief Creates a BNode object and initializes it to the specified
		filesystem entry.

	\param entry the BEntry representing the entry.
*/


/*!
	\fn BNode::BNode(const char *path)
	\brief Creates a BNode object and initializes it to the entry referred
		to by the specified path.

	\param path the path referring to the entry.
*/


/*!
	\fn BNode::BNode(const BDirectory *dir, const char *path)
	\brief Creates a BNode object and initializes it to the entry referred
		to by the specified path rooted in the specified directory.

	\param dir the BDirectory, relative to which the entry's path name is
		given.
	\param path the entry's path name relative to \a dir.
*/


/*!
	\fn BNode::BNode(const BNode &node)
	\brief Creates a copy of the given BNode.

	\param node the BNode to be copied.
*/


/*!
	\fn BNode::~BNode()
	\brief Frees all resources associated with the BNode.
*/


/*!
	\fn status_t BNode::InitCheck() const
	\brief Checks whether the object has been properly initialized or not.
	
	\returns B_OK if the object has been properly initialized, or an error
		code otherwise.
*/


/*!
	\fn status_t BNode::GetStat(struct stat *st) const
	\brief Fills in the given stat structure with the <tt>stat()</tt>
		information for this object.

	\param st a pointer to a stat structure to be filled in.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE: \c NULL \a st.
*/


/*!
	\fn int BNode::Dup()
	\brief Gets the POSIX file descriptor referred to by this node.

	Remember to call close() on the file descriptor when you're through
	with it.

	\returns a valid file descriptor, or -1 if something went wrong.
*/


/*!
	\name Assignment Methods
*/


//! @{


/*!
	\fn BNode& BNode::operator=(const BNode &node)
	\brief Initializes the object as a copy of the \a node.

	\param node the BNode to be copied.

	\returns a reference to this BNode object.
*/


/*!
	\fn status_t BNode::SetTo(const entry_ref *ref)
	\brief Initializes the object to the specified entry_ref.

	\param ref the entry_ref referring to the entry.

	\retval B_OK: Everything went fine.
	\retval B_BAD_VALUE: \c NULL \a ref.
	\retval B_ENTRY_NOT_FOUND: The entry could not be found.
	\retval B_BUSY: The entry is locked.
*/


/*!
	\fn status_t BNode::SetTo(const BEntry *entry)
	\brief Initializes the object to the specified filesystem \a entry.

	\param entry the BEntry representing the entry.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a entry.
	\retval B_ENTRY_NOT_FOUND The entry could not be found.
	\retval B_BUSY The entry is locked.
*/


/*!
	\fn status_t BNode::SetTo(const BDirectory *dir, const char *path)
	\brief Initializes the object to the entry referred by the
		specified \a path relative to the the specified directory.

	\param dir the base BDirectory.
	\param path the entry's path name relative to \a dir

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a entry.
	\retval B_ENTRY_NOT_FOUND The entry could not be found.
	\retval B_BUSY The entry is locked.
*/


/*!
	\fn void BNode::Unset()
	\brief Returns the object to an uninitialized state.
*/


//! @}


/*!
	\name Locking Methods
*/


//! @{


/*!
	\fn status_t BNode::Lock()
	\brief Attains an exclusive lock on the data referred to by this node
		so that it may not be modified by any other objects or methods.

	\retval B_OK Everything went fine.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_BUSY The node is already locked.
*/


/*!
	\fn status_t BNode::Unlock()
	\brief Unlocks the date referred to by this node.

	\retval B_OK Everything went fine.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_BAD_VALUE The node is not locked.
*/


/*!
	\fn status_t BNode::Sync()
	\brief Immediately performs any pending disk actions on the node.

	\retval B_OK Everything went fine.
	\retval B_FILE_ERROR Something went wrong.
*/


//! @}


/*!
	\name Attribute Methods
*/


//! @{


/*!
	\fn ssize_t BNode::WriteAttr(const char *attr, type_code type,
								 off_t offset, const void *buffer, size_t len)
	\brief Writes data from a buffer to an attribute.

	Write \a len bytes of data from \a buffer to the attribute specified
	by \a name after erasing any data that existed previously. The type
	specified by \a type \em is remembered, and may be queried with
	GetAttrInfo(). The value of \a offset is currently ignored.

	\param attr the name of the attribute.
	\param type the type of the attribute.
	\param offset the index at which to write the data (currently ignored).
	\param buffer the buffer containing the data to be written.
	\param len the number of bytes to be written.

	\returns the number of bytes actually written.
	\retval B_BAD_VALUE \a attr or \a buffer is \c NULL.
	\retval B_FILE_ERROR The object is not initialized or the node it refers to
		is read only.
	\retval B_NOT_ALLOWED The node resides on a read only volume.
	\retval B_DEVICE_FULL Insufficient disk space.
	\retval B_NO_MEMORY Insufficient memory to complete the operation.
*/


/*!
	\fn ssize_t BNode::ReadAttr(const char *attr, type_code type,
								off_t offset, void *buffer, size_t len) const
	\brief Reads data from an attribute into \a buffer.

	Reads \a len bytes of data from the attribute given by \a name into
	\a buffer. \a type and \a offset are currently ignored.

	\param attr the name of the attribute.
	\param type the type of the attribute (currently ignored).
	\param offset the index from which to read the data (currently ignored).
	\param buffer the buffer for the data to be read.
	\param len the number of bytes to be read.

	\returns the number of bytes actually read
	\retval B_BAD_VALUE \a attr or \a buffer is \c NULL.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_ENTRY_NOT_FOUND The node has no attribute \a attr.
*/


/*!
	\fn status_t BNode::RemoveAttr(const char *name)
	\brief Deletes the attribute given by \a name.

	\param name the name of the attribute to remove.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \a name is \c NULL.
	\retval B_FILE_ERROR The object is not initialized or the node it
		refers to read only.
	\retval B_ENTRY_NOT_FOUND The node has no attribute \a name.
	\retval B_NOT_ALLOWED The node resides on a read only volume.
*/


/*!
	\fn status_t BNode::RenameAttr(const char *oldname, const char *newname)
	\brief Moves the attribute given by \a oldname to \a newname.

	If \a newname already exists, the data is clobbered.

	\param oldname the name of the attribute to be renamed.
	\param newname the new name for the attribute.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \a oldname or \a newname is \c NULL.
	\retval B_FILE_ERROR The object is not initialized or the node it
		refers to is read only.
	\retval B_ENTRY_NOT_FOUND The node has no attribute \a oldname.
	\retval B_NOT_ALLOWED The node resides on a read only volume.
*/


/*!
	\fn status_t BNode::GetAttrInfo(const char *name,
									struct attr_info *info) const
	\brief Fills in the pre-allocated attr_info struct pointed to by \a info
		with information about the attribute specified by \a name.

	\param name the name of the attribute
	\param info the attr_info structure to be filled in

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \a name is \c NULL.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_ENTRY_NOT_FOUND The node has no attribute \a name.
*/


/*!
	\fn status_t BNode::GetNextAttrName(char *buffer)
	\brief Copies the name of the attribute into \c buffer and then advances
		the pointer to the next attribute.

	The name of the node is first copied into \a buffer, which should be at
	least \c B_ATTR_NAME_LENGTH characters long. The copied node name is
	\c NUL terminated. Once the name is copied the attribute list pointer
	is advanced to the next attribute in the list. When GetNextAttrName()
	reaches the end of the list it returns \c B_ENTRY_NOT_FOUND.

	\param buffer A buffer to copy the name of the attribute into.

	\retval B_OK The Attribute name was copied and there are more attribute
		names to copy.
	\retval B_BAD_VALUE passed in \a buffer is \c NULL.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_ENTRY_NOT_FOUND There are no more attributes, the last attribute
		name has already been copied.
*/


/*!
	\fn status_t BNode::RewindAttrs()
	\brief Resets the object's attribute pointer to the first attribute in the
		list.

	\retval B_OK Everything went fine.
	\retval B_FILE_ERROR Some other error occurred.
*/


/*!
	\fn status_t BNode::WriteAttrString(const char *name, const BString *data)
	\brief Writes the specified string to the specified attribute, clobbering
		any previous data.

	\param name the name of the attribute.
	\param data the BString to be written to the attribute.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a name or \a data
	\retval B_FILE_ERROR The object is not initialized or the node it refers to
		is read only.
	\retval B_NOT_ALLOWED The node resides on a read only volume.
	\retval B_DEVICE_FULL Insufficient disk space.
	\retval B_NO_MEMORY Insufficient memory to complete the operation.
*/


/*!
	\fn status_t BNode::ReadAttrString(const char *name, BString *result) const
	\brief Reads the data of the specified attribute into the pre-allocated
		\a result.

	\param name the name of the attribute.
	\param result the BString to be set to the value of the attribute.

	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \a name or \a result is \c NULL.
	\retval B_FILE_ERROR The object is not initialized.
	\retval B_ENTRY_NOT_FOUND The node has no attribute \a attr.
*/


//! @}


/*!
	\name Comparison Methods
*/


//! @{


/*!
	\fn bool BNode::operator==(const BNode &node) const
	\brief Tests whether this and the supplied BNode object are equal.

	Two BNode objects are said to be equal if they're set to the same node,
	or if they're both \c B_NO_INIT.

	\param node the BNode to be compared with.

	\return \c true, if the BNode objects are equal, \c false otherwise.
*/


/*!
	\fn bool BNode::operator!=(const BNode &node) const
	\brief Tests whether this and the supplied BNode object are not equal.

	Two BNode objects are said to be equal if they're set to the same node,
	or if they're both \c B_NO_INIT.

	\param node the BNode to be compared with

	\return \c false, if the BNode objects are equal, \c true otherwise.
*/


//! @}


/*!
	\name Private Methods
*/


//! @{


/*!
	\fn status_t BNode::set_fd(int fd)
	\brief Sets the node's file descriptor.

	Used by each implementation (i.e. BNode, BFile, BDirectory, etc.) to set
	the node's file descriptor. This allows each subclass to use the various
	file-type specific system calls for opening file descriptors.

	\note This method calls close_fd() to close previously opened FDs. Thus
		derived classes should take care to first call set_fd() and set
		class specific resources freed in their close_fd() version
		thereafter.

	\param fd the file descriptor this BNode should be set to (may be -1).

	\returns \c B_OK if everything went fine, or an error code if something
		went wrong.
*/


/*!
	\fn void BNode::close_fd()
	\brief Closes the node's file descriptor(s).

	To be implemented by subclasses to close the file descriptor using the
	proper system call for the given file-type. This implementation calls
	_kern_close(fFd) and also _kern_close(fAttrDir) if necessary.
*/


/*!
	\fn void BNode::set_status(status_t newStatus)
	\brief Sets the BNode's status.

	To be used by derived classes instead of accessing the BNode's private
	\c fCStatus member directly.

	\param newStatus the new value for the status variable.
*/


/*!
	\fn status_t BNode::_SetTo(int fd, const char *path, bool traverse)
	\brief Initializes the BNode's file descriptor to the node referred to
		 by the given FD and path combo.

	\a path must either be \c NULL, an absolute or a relative path.
	In the first case, \a fd must not be \c NULL; the node it refers to will
	be opened. If absolute, \a fd is ignored. If relative and \a fd is >= 0,
	it will be reckoned off the directory identified by \a fd, otherwise off
	the current working directory.

	The method will first try to open the node with read and write permission.
	If that fails due to a read-only FS or because the user has no write
	permission for the node, it will re-try opening the node read-only.

	The \a fCStatus member will be set to the return value of this method.

	\param fd Either a directory FD or a value < 0. In the latter case \a path
		   must be specified.
	\param path Either \a NULL in which case \a fd must be given, absolute, or
		   relative to the directory specified by \a fd (if given) or to the
		   current working directory.
	\param traverse If the node identified by \a fd and \a path is a symlink
		   and \a traverse is \c true, the symlink will be resolved recursively.

	\returns \c B_OK if everything went fine, or an error code if something
		went wrong.
*/


/*!
	\fn status_t BNode::_SetTo(const entry_ref *ref, bool traverse)
	\brief Initializes the BNode's file descriptor to the node referred to
		 by the given entry_ref.

	The method will first try to open the node with read and write permission.
	If that fails due to a read-only FS or because the user has no write
	permission for the node, it will re-try opening the node read-only.

	The \a fCStatus member will be set to the return value of this method.

	\param ref An entry_ref identifying the node to be opened.
	\param traverse If the node identified by \a ref is a symlink and
		\a traverse is \c true, the symlink will be resolved recursively.

	\returns \c B_OK if everything went fine, or an error code if something
		went wrong.
*/


/*!
	\fn status_t BNode::set_stat(struct stat &st, uint32 what)
	\brief Modifies a certain setting for this node based on \a what and the
		corresponding value in \a st.

	Inherited from and called by BStatable.

	\param st a stat structure containing the value to be set.
	\param what specifies what setting to be modified.

	\returns \c B_OK if everything went fine, or an error code if something
		went wrong.
*/


/*!
	\fn status_t BNode::InitAttrDir()
	\brief Verifies that the BNode has been properly initialized, and then
		(if necessary) opens the attribute directory on the node's file
		descriptor, storing it in fAttrDir.

	\returns \c B_OK if everything went fine, or an error code if something
		went wrong.
*/


//! @}