haiku/docs/user/storage/Entry.dox

/*
 * Copyright 2011 Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Authors:
 *		Tyler Dauwalder
 *		Simon Cusack, scusack@users.sf.net
 *		John Scipione, jscipione@gmail.com
 *
 * Corresponds to:
 *		headers/os/storage/Entry.h  hrev43528
 *		src/kits/storage/Entry.cpp  hrev43528
 */


/*!
	\file Entry.h
	\ingroup storage
	\ingroup libbe
	\brief Provides the BEntry class and entry_ref implementations.
*/


/*!
	\struct entry_ref
	\ingroup storage
	\ingroup libbe
	\brief A filesystem entry represented as a name in a concrete directory.

	entry_refs may refer to pre-existing (concrete) files, as well as
	non-existing (abstract) files. However, the parent directory of the file
	\b must exist.

	The result of this dichotomy is a blending of the persistence gained by
	referring to entries with a reference to their internal filesystem node and
	the flexibility gained by referring to entries by name.

	For example, if the directory in which the entry resides (or a directory
	further up in the hierarchy) is moved or renamed, the entry_ref will still
	refer to the correct file (whereas a pathname to the previous location of
	the file would now be invalid).

	On the other hand, say that the entry_ref refers to a concrete file. If the
	file itself is renamed, the entry_ref now refers to an abstract file with
	the old name (the upside in this case is that abstract entries may be
	represented by entry_refs without preallocating an internal filesystem node
	for them).
*/


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


/*!
	\fn entry_ref::entry_ref(dev_t dev, ino_t dir, const char* name)
	\brief Creates an entry_ref object initialized to the given file name in
		the given directory on the given device.

	\a name may refer to either a pre-existing file in the given directory, or
	a non-existent file. No explicit checking is done to verify validity of the
	given arguments, but later use of the entry_ref will fail if \p dev is not
	a valid device or \a dir is a not a directory on \p dev.

	\param dev the device on which the entry's parent directory resides
	\param dir the directory in which the entry resides
	\param name the leaf name of the entry, which is not required to exist
*/


/*!
	\fn entry_ref::entry_ref(const entry_ref& ref)
	\brief Returns a copy of the passed in entry_ref object.

	\param ref A reference to an entry_ref to copy.
*/


/*!
	\fn entry_ref::~entry_ref()
	\brief Destroys the object and frees the storage allocated for the leaf
		name, if necessary.
*/


/*!
	\fn status_t entry_ref::set_name(const char* name)
	\brief Set the entry_ref's leaf name, freeing the storage allocated for any
		previous name and then making a copy of the new name.

	\param name Pointer to a null-terminated string containing the new name for
		the entry. May be \c NULL.
*/


/*!
	\fn bool entry_ref::operator==(const entry_ref& ref) const
	\brief Compares the entry_ref object with the passed in entry_ref,
		returning \c true if they are equal.

	\returns \c true if he entry_refs are equal, \c false otherwise.
*/


/*!
	\fn bool entry_ref::operator!=(const entry_ref& ref) const
	\brief Compares the entry_ref object with the passed in entry_ref,
		returning \c true if they are NOT equal.

	\returns \c true if the entry_refs are NOT equal, \c false otherwise.
*/


/*!
	\fn entry_ref& entry_ref::operator=(const entry_ref& ref)
	\brief Makes the entry_ref object a copy of the passed in entry_ref.

	\param ref The entry_ref to copy.

	\returns A pointer to the resulting entry_ref copy.
*/


/*!
	\var dev_t entry_ref::device

	The device id of the storage device on which the entry resides.

*/


/*!
	\var ino_t entry_ref::directory

	The inode number of the directory in which the entry resides.
*/


/*!
	\var char *entry_ref::name

	The leaf name of the entry
*/


/*!
	\class BEntry
	\ingroup storage
	\ingroup libbe
	\brief A location in the filesystem.

	The BEntry class defines objects that represent "locations" in the file
	system hierarchy. Each location (or entry) is given as a name within a
	directory. For example, if you create a BEntry like this:

\code
BEntry entry("/boot/home/fido");
\endcode

	the resulting BEntry object represents the location of the file \c fido
	within the <tt>/boot/home</tt> directory.
*/


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

	Should be followed by a call to one of the SetTo() methods, or an
	assignment.
	- SetTo(const BDirectory*, const char*, bool)
	- SetTo(const entry_ref*, bool)
	- SetTo(const char*, bool)
	- operator=(const BEntry&)
*/


/*!
	\fn BEntry::BEntry(const BDirectory* dir, const char* path, bool traverse)
	\brief Creates a BEntry initialized to the given directory and path
		combination.

	If traverse is \c true and \a path refers to a symlink, the BEntry will
	refer to the linked file; if \c false, the BEntry will refer to the
	symlink itself.

	\param dir The base directory in which the \a path resides.
	\param path Relative path based off of \a dir.
	\param traverse Whether or not to traverse symbolic links.

	\see BEntry::SetTo(const BDirectory*, const char *, bool)
*/


/*!
	\fn BEntry::BEntry(const entry_ref* ref, bool traverse)
	\brief Creates a BEntry for the file referred to by the passed in
		entry_ref.

	If traverse is \c true and \a ref refers to a symlink, the BEntry
	will refer to the linked file; if \c false, the BEntry will refer
	to the symlink itself.

	\param ref The entry_ref referring to the given file.
	\param traverse Whether or not symlinks are to be traversed.

	\sa BEntry::SetTo(const entry_ref*, bool)
*/


/*!
	\fn BEntry::BEntry(const char* path, bool traverse)
	\brief Creates a BEntry initialized to the given path.

	If \a path is relative, it will be reckoned off the current working
	directory. If \a path refers to a symlink and traverse is \c true, the
	BEntry will refer to the linked file. If traverse is \c false, the
	BEntry will refer to the symlink itself.

	\param path The path of the file.
	\param traverse Whether or not symlinks are to be traversed.

	\sa BEntry::SetTo(const char*, bool)
*/


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

	\param entry the entry to be copied

	\sa operator=(const BEntry&)
*/


/*!
	\fn BEntry::~BEntry()
	\brief Frees all of the allocated resources of the BEntry.

	\sa Unset()
*/


/*!
	\fn status_t BEntry::InitCheck() const
	\brief Returns the result of the most recent construction or SetTo() call.

	\returns A status code.
	\retval B_OK Success
	\retval B_NO_INIT The object has been Unset() or is uninitialized.
*/


/*!
	\fn bool BEntry::Exists() const
	\brief Returns whether or not the entry exists in the filesystem.

	\returns \c true if the entry exists, \c false if not.
*/


/*!
	\fn status_t BEntry::GetStat(struct stat *result) const
	\brief Fills in a stat structure for the entry.

	The information is copied into the \c stat structure pointed to
	by \a result.

	\note The BStatable object does not cache the stat structure -- each time
		you call GetStat() fresh stat information is retrieved.

	\param result A pointer to a pre-allocated structure into which the stat
		information is copied.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::SetTo(const BDirectory* dir, const char* path,
		bool traverse)
	\brief Reinitializes the BEntry to the path or directory path combination,
		resolving symlinks if traverse is \c true.

	\param dir The base directory in which the \a path resides.
	\param path Relative path based off of \a dir.
	\param traverse Whether or not to traverse symbolic links.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::SetTo(const entry_ref* ref, bool traverse)
	\brief Reinitializes the BEntry to the passed in entry_ref object
		resolving symlinks if traverse is \c true.

	\param ref The entry_ref referring to the given file.
	\param traverse Whether or not symlinks are to be traversed.

	\returns \c B_OK on success, or an error code on failure.

	\sa BEntry::BEntry(const entry_ref* ref, bool traverse)
*/


/*!
	\fn status_t BEntry::SetTo(const char* path, bool traverse)
	\brief Reinitializes the BEntry object to the path, resolving symlinks if
		traverse is \c true.

	\param path The path of the file.
	\param traverse Whether or not symlinks are to be traversed.

	\returns \c B_OK on success, or an error code on failure.

	\sa BEntry::BEntry(const char* path, bool traverse)
*/


/*!
	void BEntry::Unset()
	\brief Reinitializes the BEntry to an uninitialized BEntry object
*/


/*!
	\fn status_t BEntry::GetRef(entry_ref* ref) const
	\brief Gets an entry_ref structure for the BEntry.

	\param ref A pointer to a preallocated entry_ref object into which the
		result is copied.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::GetPath(BPath* path) const
	\brief Gets the path for the BEntry.

	\param path A pointer to a pre-allocated BPath object into which the
		result is copied.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::GetParent(BEntry* entry) const
	\brief Gets the parent of the BEntry as a BEntry.

	If the function fails, the argument is Unset(). Destructive calls to
	GetParent() are allowed, i.e.:

\code
BEntry entry("/boot/home/fido");
status_t err;
char name[B_FILE_NAME_LENGTH];

// Spit out the path components backwards, one at a time.
do {
	entry.GetName(name);
	printf("> %s\n", name);
} while ((err=entry.GetParent(&entry)) == B_OK);

// Complain for reasons other than reaching the top.
if (err != B_ENTRY_NOT_FOUND)
	printf(">> Error: %s\n", strerror(err));
\endcode

	will output:

\code
> fido
> home
> boot
> .
\endcode

	\param entry A pointer to a pre-allocated BEntry object into which the
		result is stored.

	\returns A status code.
	\retval B_OK Success
	\retval B_ENTRY_NOT_FOUND Attempted to get the parent of the root
		directory.
*/


/*!
	\fn status_t BEntry::GetParent(BDirectory* dir) const
	\brief Gets the parent of the BEntry as a BDirectory.

	If the function fails, the argument is Unset().

	\param dir A pointer to a pre-allocated BDirectory object into which the
		result is copied.

	\returns A status code.
	\retval B_OK Success
	\retval B_ENTRY_NOT_FOUND Attempted to get the parent of the root
		directory.
*/


/*!
	\fn status_t BEntry::GetName(char* buffer) const
	\brief Gets the name of the leaf of the BEntry object.

	\c buffer must be pre-allocated and of sufficient length to hold the
	entire string. A length of \c B_FILE_NAME_LENGTH is recommended.

	\param buffer A pointer to a pre-allocated string into which the result
		is copied.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::Rename(const char* path, bool clobber)
	\brief Renames the BEntry to \a path replacing an existing entry
		if \a clobber is \c true.

	\note The BEntry object must refer to an existing file, if it is abstract,
		this method will fail.

	\param path A pointer to a string containing the new name for the entry.
		It may be an absolute or relative path. If it is a relative path the
		entry is renamed within its current directory.
	\param clobber If \c false and a file with the name given by \c path
		already exists, the method will fail. If \c true and such a file
		exists, it will be overwritten.

	\returns A status code.
	\retval B_OK Success
	\retval B_ENTRY_EXISTS The new location already exists and \c clobber
		is \c false.
	\retval B_ENTRY_NOT_FOUND Attempted to rename an abstract entry.
*/


/*!
	\fn status_t BEntry::MoveTo(BDirectory* dir, const char* path,
		bool clobber)
	\brief Moves the BEntry to directory or directory and path combination,
		replacing an existing entry if clobber is true.

	\note The BEntry object must refer to an existing file, if it is abstract,
		this method will fail.

	\param dir A pointer to a pre-allocated BDirectory into which the entry
		should be moved.
	\param path (optional) new leaf name for the entry. May be a simple leaf
		or a relative path; either way, \c path is reckoned off of \c dir. If
		\c NULL, the entry retains its previous leaf name.
	\param clobber If \c false and an entry already exists at the specified
		destination, the method will fail. If \c true and such an entry exists,
		it will be overwritten.

	\returns A status code.
	\retval B_OK Success
	\retval B_ENTRY_EXISTS The new location already exists and \c clobber
		is \c false.
	\retval B_ENTRY_NOT_FOUND Attempted to rename an abstract entry.
*/


/*!
	\fn status_t BEntry::Remove()
	\brief Removes the entry from the file system.

	\note If any file descriptors are open on the file when Remove() is called
	the chunk of data they refer to will continue to exist until all such file
	descriptors are closed. The BEntry object, however, becomes abstract and
	no longer refers to any actual data in the filesystem.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn bool BEntry::operator==(const BEntry& item) const
	\brief Returns \c true if the BEntry and \a item refer to the same entry
		or if they are both uninitialized.

	\retval true Both BEntry objects refer to the same entry or they are
		both uninitialized.
	\retval false The BEntry objects refer to different entries.
*/


/*!
	\fn bool BEntry::operator!=(const BEntry& item) const
	\brief Returns false if the BEntry and \c item refer to the same entry or
		if they are both uninitialized.

	\retval true The BEntry objects refer to different entries.
	\retval false Both BEntry objects refer to the same entry or they are
		both uninitialized.
*/


/*!
	\fn BEntry& BEntry::operator=(const BEntry& item)
	\brief Reinitializes the BEntry to be a copy of \a item.

	\returns A pointer to the copy.
*/


/*!
	\fn status_t BEntry::set_stat(struct stat& st, uint32 what)
	\brief Updates the BEntry with the data from the stat structure according
		to the \a what mask.

	\param st The stat structure to set.
	\param what A mask

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_FILE_ERROR There was an error writing to the BEntry object.
*/


/*!
	\fn status_t BEntry::_SetTo(int dirFD, const char* path, bool traverse)
	\brief Sets the entry to point to the entry specified by the path \a path
	relative to the given directory.

	If \a traverse is \c true and the given entry is a symbolic link, the
	object is recursively set to point to the entry pointed to by the symlink.

	If \a path is an absolute path, \a dirFD is ignored.

	If \a dirFD is -1, \a path is considered relative to the current directory
	(unless it is an absolute path).

	The ownership of the file descriptor \a dirFD is transferred to the
	method, regardless of whether it succeeds or fails. The caller must not
	close the FD afterwards.

	\param dirFD File descriptor of a directory relative to which path is to
		be considered. May be -1 if the current directory shall be considered.
	\param path Pointer to a path relative to the given directory.
	\param traverse If \c true and the given entry is a symbolic link, the
		object is recursively set to point to the entry linked to by the
		symbolic link.

	\returns \c B_OK on success, or an error code on failure.
*/


/*!
	\fn status_t BEntry::_SetName(const char* name)
	\brief Handles string allocation, deallocation, and copying for the
		leaf name of the entry.

	\param name The leaf \a name of the entry.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \a name is \c NULL.
	\retval B_NO_MEMORY Ran out of memory trying to allocate \a name.
*/


/*!
	\fn status_t BEntry::_Rename(BEntry& target, bool clobber)
	\brief Renames the entry referred to by this object to the location
		specified by \a target.

	If an entry exists at the target location, the method fails, unless
	\a clobber is \c true, in which case that entry is overwritten (doesn't
	work for non-empty directories, though).

	If the operation was successful, this entry is made a clone of the
	supplied one and the supplied one is uninitialized.

	\param target The entry specifying the target location.
	\param clobber If \c true, the an entry existing at the target location
		   will be overwritten.

	\return \c B_OK, if everything went fine, another error code otherwise.
*/


/*!
	\fn void BEntry::_Dump(const char* name)
	\brief Debugging function, dumps the given entry to stdout.

	\param name A pointer to a string to be printed along with the dump for
		identification purposes.
*/


/*!
	\fn status_t get_ref_for_path(const char* path, entry_ref* ref)
	\brief Returns an entry_ref for a given path.

	\param path The path name referring to the entry.
	\param ref The entry_ref structure to be filled in.

	\returns A status code.
	\retval B_OK Everything went fine.
	\retval B_BAD_VALUE \c NULL \a path or \a ref.
	\retval B_ENTRY_NOT_FOUND A (non-leaf) path component does not exist.
	\retval B_NO_MEMORY Insufficient memory for successful completion.
*/


/*!
	\fn bool operator<(const entry_ref& a, const entry_ref& b)
	\brief Returns whether an entry is less than another.

	The components are compared in order \c device, \c directory, \c name.
	A \c NULL \c name is less than any non-<tt>NULL</tt> name.

	\retval true a < b
	\retval false a >= b
*/