Key

Key is an essential class that encapsulates key name , value and metainfo . More...

Collaboration diagram for Key:

Modules
	Meta Info Manipulation Methods
	Methods to do various operations on Key metadata.
	Methods for Making Tests
	Methods to do various tests on Keys.
	Name Manipulation Methods
	Methods to do various operations on Key names.
	Value Manipulation Methods
	Methods to do various operations on Key values.

Macros
#define	KDB_PATH_SEPARATOR   '/'
	/ is used to separate key names. More...
#define	KDB_PATH_ESCAPE   '\\'
	\ is used as escape character in the key name. More...

Enumerations
enum	elektraKeyFlags {   KEY_VALUE = 1 << 1 , KEY_FLAGS = 3 , KEY_BINARY = 1 << 4 , KEY_SIZE = 1 << 11 ,   KEY_META = 1 << 15 , KEY_NULL = 1 << 16 , KEY_END = 0 }
	Allows keyNew() to determine which information comes next. More...
enum	elektraCopyFlags {   KEY_CP_NAME = 1 << 0 , KEY_CP_STRING = 1 << 1 , KEY_CP_VALUE = 1 << 2 , KEY_CP_META = 1 << 3 ,   KEY_CP_ALL = KEY_CP_NAME | KEY_CP_VALUE | KEY_CP_META }
	Copy options. More...
enum	elektraLockFlags { KEY_LOCK_NAME = 1 << 17 , KEY_LOCK_VALUE = 1 << 18 , KEY_LOCK_META = 1 << 19 }
	Lock options. More...
enum	elektraNamespace {   KEY_NS_NONE = 0 , KEY_NS_CASCADING = 1 , KEY_NS_META = 2 , KEY_NS_SPEC = 3 ,   KEY_NS_PROC = 4 , KEY_NS_DIR = 5 , KEY_NS_USER = 6 , KEY_NS_SYSTEM = 7 ,   KEY_NS_DEFAULT = 8 }
	Elektra currently supported Key namespaces. More...

Functions
Key *	keyNew (const char *name,...)
	A practical way to fully create a Key object in one step. More...
Key *	keyCopy (Key *dest, const Key *source, elektraCopyFlags flags)
	Copy or clear a key. More...
int	keyDel (Key *key)
	A destructor for Key objects. More...
int	keyClear (Key *key)
	Will clear all internal data of a Key. More...
uint16_t	keyIncRef (Key *key)
	Increment the reference counter of a Key object. More...
uint16_t	keyDecRef (Key *key)
	Decrement the reference counter of a Key object. More...
uint16_t	keyGetRef (const Key *key)
	Return the current reference counter value of a Key object. More...
int	keyLock (Key *key, elektraLockFlags what)
	Permanently lock parts of a Key. More...
int	keyIsLocked (const Key *key, elektraLockFlags what)
	Checks which parts of a Key are locked. More...

Detailed Description

Key is an essential class that encapsulates key name , value and metainfo .

To use it include:

#include <kdb.h>

Key properties are:

• Key name
• Key value
• Key metadata , including but not limited to:
  • Key comment
  • Key owner
  • UID, GID and filesystem-like mode permissions
  • Mode, change and modification times

ABI

Due to ABI compatibility, the Key structure is not defined in kdb.h, only declared. So you can only declare pointers to Keys in your program, and allocate and free memory for them with keyNew() and keyDel() respectively.

Reference Counting

Every key has its reference counter (see keyGetRef() for longer explanation) that will be initialized with 0, that means a subsequent call of keyDel() will delete the key. If you append the key to a keyset the reference counter will be incremented by one (see keyIncRef()) and the key can't be deleted by a keyDel().

As you can imagine this refcounting allows you to put the Key in your own data structures. It can be a very powerful feature, e.g. if you need your own-defined ordering or different Models of your configuration.

Copy-On-Write

Keys employ copy-on-write techniques to minimize memory footprint. If keys are copied or duplicated, they will point at the same name and value as the source key. Only if this data is changed, additional memory is allocated.

Macro Definition Documentation

KDB_PATH_ESCAPE

#define KDB_PATH_ESCAPE   '\\'

\ is used as escape character in the key name.

See also

description about key names .

KDB_PATH_SEPARATOR

#define KDB_PATH_SEPARATOR   '/'

/ is used to separate key names.

See also

description about key names .

Enumeration Type Documentation

elektraCopyFlags

enum elektraCopyFlags

Copy options.

See also

keyCopy()

Enumerator
KEY_CP_NAME	Flag for copying the key name
KEY_CP_STRING	Flag for copying the key value, if it is a string
KEY_CP_VALUE	Flag for copying the key value
KEY_CP_META	Flag for copying the key metadata
KEY_CP_ALL	Shorthand for copying name, value and metadata

elektraKeyFlags

enum elektraKeyFlags

Allows keyNew() to determine which information comes next.

See also

keyNew()

Enumerator
KEY_VALUE	Flag for the key data
KEY_FLAGS	Allows to define multiple flags at once.
KEY_BINARY	Flag if the key is binary
KEY_SIZE	Flag for maximum size to limit value
KEY_META	Flag for metadata
KEY_NULL	Is not a flag, only as return value Deprecated: do not use
KEY_END	Used as a parameter terminator to keyNew()

elektraLockFlags

enum elektraLockFlags

Lock options.

See also

keyLock(), keyIsLocked()

Enumerator
KEY_LOCK_NAME	lock the name of a key
KEY_LOCK_VALUE	lock the value of a key
KEY_LOCK_META	lock the meta data of a key

elektraNamespace

enum elektraNamespace

Elektra currently supported Key namespaces.

See also

kdbGet(), keyGetNamespace()

Enumerator
KEY_NS_NONE	no key given as parameter to keyGetNamespace()
KEY_NS_CASCADING	cascading key, starts with /, abstract name for any of the namespaces below
KEY_NS_META	metakey, i.e. any key name not under other categories
KEY_NS_SPEC	spec contains the specification of the other namespaces
KEY_NS_PROC	proc contains process-specific configuration
KEY_NS_DIR	dir contains configuration from a specific directory
KEY_NS_USER	user key in the home directory of the current user
KEY_NS_SYSTEM	system key is shared for a computer system
KEY_NS_DEFAULT	default key used as a fallback if no other key is found

Function Documentation

keyClear()

int keyClear

(

Key *

key

)

Will clear all internal data of a Key.

After this call you will receive a fresh Key - with no value, metadata or name.

The reference counter will stay unmodified.

Note

that you might also clear() all aliases with this operation.

int f (Key *k)
{
        keyClear (k);
        // you have a fresh Key k here
        keySetString (k, "value");
        // the caller will get an empty Key k with an value
}

Postcondition

key's name is "/"

key's metadata is empty

Parameters

key	the Key that should be cleared

Return values

0	on success
-1	on NULL pointer

Since

1.0.0

See also

keyDel() for completely deleting a Key

keyCopy()

Key* keyCopy	(	Key *	dest,
		const Key *	source,
		elektraCopyFlags	flags
	)

Copy or clear a key.

Depending on the chosen flags keyCopy() only copies certain parts of source into dest.

• If KEY_CP_NAME is set, the key name will be copied from source to dest.
• If KEY_CP_META is set, the meta keys will be copied from source to dest.
• If KEY_CP_VALUE is set, the key value will be copied from source to dest. Additionally, if source is a binary key (keyIsBinary()), dest will also be marked as binary. This means that even if KEY_CP_META is not set, the binary meta key will be copied with KEY_CP_VALUE.
• If KEY_CP_STRING is set, the key value will be copied from source to dest, but only, if source is not a binary key (keyIsBinary()). If source is binary, keyCopy() fails. If dest is binary, it will still be marked as binary after the copy. This cannot be used together with KEY_CP_VALUE. The main purpose of KEY_CP_STRING is for copying into known string keys. It ensure that you don't accidentally convert string keys into binary keys.

There is also the shorthand KEY_CP_ALL. It is equivalent to KEY_CP_NAME | KEY_CP_VALUE | KEY_CP_META, i.e. all key data supported by keyCopy() will be copied from source to dest.

Use this function when you need to copy into an existing key, e.g. because it was passed by a pointer in a function you can do so:

keyCopy (copy, orig, KEY_CP_ALL);

Most often you will want to duplicate an existing key. For this purpose the alias keyDup() exists. Calling

copy = keyDup (orig, KEY_CP_ALL);

is equivalent to

copy = keyCopy (keyNew ("/", KEY_END), orig, KEY_CP_ALL);

The reference counter will not be changed for both keys. Affiliation to keysets are also not affected.

Since metadata uses copy-on-write semantics there is only a constant memory cost to copying metadata.

When you pass a NULL-pointer as source the pieces of dest specified by flags will be cleared.

Calling keyCopy (dest, NULL, KEY_CP_ALL) is different from calling keyClear(). The key will not be fully reset, the reference counter and internal flags will remain unchanged. Additionally, keyCopy() respects keyLock() state, while keyClear() always works.

keyCopy (k, NULL, KEY_CP_ALL);
// name, value and metadata of k have now been clear
// lock flags, reference count, etc. remain unchanged

Precondition

dest must be a valid Key (created with keyNew)

dest must not have read-only flags set

source must be a valid Key or NULL

Invariant

Key name stays valid until delete

Postcondition

Value from Key source is written to Key dest

Parameters

dest	the key which will be written to
source	the key which should be copied or NULL to clear the data of dest
flags	specifies which parts of the key should be copied

Returns

dest

Return values

NULL	on memory allocation problems
NULL	when a part of dest that should be modified (e.g. name, value) was marked read-only, e.g. the name of dest will be read-only if dest is part of a KeySet
NULL	when dest is NULL
NULL	when both KEY_CP_VALUE and KEY_CP_STRING are set in flags
NULL	when both KEY_CP_STRING is set in flags and source is a binary key (keyIsBinary())

Since

0.9.5

See also

keyDup() for duplicating an existing Key

keyDecRef()

uint16_t keyDecRef

(

Key *

key

)

Decrement the reference counter of a Key object.

As long as the reference counter is non-zero, keyDel() operations on key will be a no-op and return an error code.

Postcondition

key's reference counter is >= 0

key's reference counter is < SSIZE_MAX

Parameters

key	the Key object whose reference counter should get decreased

Returns

the updated value of the reference counter

Return values

UINT16_MAX	on NULL pointer
0	when the reference counter already was the minimum value 0, the reference counter will not be modified in this case

Since

1.0.0

See also

keyGetRef() to retrieve the current reference count

keyIncRef() for increasing the reference counter and for a more complete explanation of the reference counting system

keyDel() for deleting a Key

keyDel()

int keyDel

(

Key *

key

)

A destructor for Key objects.

Every Key created by keyNew() must be deleted with keyDel().

When the reference counter of key is non-zero, this function will do nothing and simply return the current value of the reference counter.

It is therefore safe to call keyDel (k) on any Key * k.

Postcondition

all memory related to key will be freed

Parameters

key	the Key object to delete

Return values

0	when the Key was freed
-1	on NULL pointers

Returns

the value of the reference counter, if it was non-zero

Since

1.0.0

See also

keyNew() for creating a new Key

keyIncRef() for more information about the reference counter

keyGetRef()

uint16_t keyGetRef

(

const Key *

key

)

Return the current reference counter value of a Key object.

Parameters

key	the Key whose reference counter to retrieve

Returns

the value of the key's reference counter

Return values

-1	on NULL pointer

Since

1.0.0

See also

keyIncRef() for increasing the reference counter and for a more complete explanation of the reference counting system

keyDecRef() for decreasing the reference counter

keyIncRef()

uint16_t keyIncRef

(

Key *

key

)

Increment the reference counter of a Key object.

As long as the reference counter is non-zero, keyDel() operations on key will be a no-op and return an error code.

Elektra's system for reference counting is not based on a concept of shared ownership. It is more similar to a shared lock, where the counter is used to keep track of how many clients hold the lock.

Initially, the reference counter will be 0. This is can be interpreted as the lock being unlocked. When you increment the reference counter, the lock becomes locked and keyDel() is blocked and fails. Only when the reference counter is fully decremented back down to 0 again, will keyDel() work again.

Note

The reference counter can never exceed UINT16_MAX - 1. UINT16_MAX is reserved as an error code.

Postcondition

key's reference counter is > 0

key's reference counter is <= UINT16_MAX - 1

Parameters

key	the Key object whose reference counter should be increased

Returns

the updated value of the reference counter

Return values

UINT16_MAX	on NULL pointer
UINT16_MAX	when the reference counter already was the maximum value UINT16_MAX - 1, the reference counter will not be modified in this case

Since

1.0.0

See also

keyGetRef() to retrieve the current reference count

keyDecRef() for decreasing the reference counter

keyDel() for deleting a Key

keyIsLocked()

int keyIsLocked	(	const Key *	key,
		elektraLockFlags	what
	)

Checks which parts of a Key are locked.

Parameters

key	the Key that should be checked for locks
what	the parts of the Key that should checked for locks

Returns

the bits that are locked

Return values

0	if nothing is locked
-1	on error (NULL pointer)

Since

1.0.0

See also

keyLock() for locking a Key

keyLock()

int keyLock	(	Key *	key,
		elektraLockFlags	what
	)

Permanently lock parts of a Key.

This can be:

• KEY_LOCK_NAME to lock the name
• KEY_LOCK_VALUE to lock the value
• KEY_LOCK_META to lock the metadata

To unlock the Key, duplicate it.

It is also possible to lock the Key when it is created with keyNew().

Some data structures need to lock the Key (most likely its name), so that the ordering does not get confused.

Postcondition

keyIsLocked(key, what) == what

Parameters

key	the Key that should be locked
what	the parts of the Key that should be locked (see above)

Returns

the bits that were successfully locked

Return values

0	if everything was locked before
-1	if it could not be locked (NULL pointer)

Since

1.0.0

See also

keyIsLocked() for checking whether a Key is locked

keyNew() for creating a new Key

keyDup() for duplicating an existing Key

ksAppendKey() appends a Key to a KeySet (and locks it)

keyNew()

Key* keyNew	(	const char *	name,
			...
	)

A practical way to fully create a Key object in one step.

To just get a key object, simple do:

// Create and initialize a key with a name and nothing else
Key *k=keyNew("user:/some/example", KEY_END);
// work with it
keyDel (k);

keyNew() allocates memory for a key object and keyDel() cleans everything up.

If you want the key object to contain a name, value, comment and other meta info read on.

Note

When you already have a key with similar properties its easier to keyDup() the key.

You can call keyNew() in many different ways depending on the attribute tags you pass as parameters. Tags are represented as elektraKeyFlags values, and tell keyNew() which Key attribute comes next. The Key attribute tags are the following:

• KEY_VALUE
  Next parameter is a pointer to the value that will be used. If no KEY_BINARY was used before, a string is assumed.

  // Create and initialize a key with a name and nothing else
  Key *k=keyNew("user:/tmp/ex0",
          KEY_VALUE, "some data",    // set a string value
          KEY_END);                  // end of args

• KEY_SIZE
  Define a maximum length of the value. This is only used when setting a binary key.

  // Create and initialize a key with a name and nothing else
  Key *k=keyNew("user:/tmp/ex1",
          KEY_SIZE, 4,               // has no effect on strings
          KEY_VALUE, "some data",    // set a string value
          KEY_END);                  // end of args

• KEY_META
  Next two parameter is a metaname and a metavalue. See keySetMeta().

  Key *k=keyNew("user:/tmp/ex3",
          KEY_META, "comment/#0", "a comment",  // with a comment
          KEY_META, "owner", "root",         // and an owner
          KEY_META, "special", "yes",        // and any other metadata
          KEY_END);                  // end of args

• KEY_END
  Must be the last parameter passed to keyNew(). It is always required, unless the keyName is 0.
• KEY_FLAGS
  Bitwise disjunction of flags, which don't require one or more values. recommended way to set multiple flags. overrides previously defined flags.

  Key *k=keyNew("user:/tmp/ex3",
          KEY_BINARY,                     // binary key
          KEY_SIZE, 7,                    // assume binary length 7
          KEY_VALUE, "some data",         // value that will be truncated in 7 bytes
          KEY_END);                       // end of args

• KEY_BINARY
  Allows one to change the key to a binary key. Make sure that you also pass KEY_SIZE before you set the value. Otherwise it will be cut off with first \0 in the string. So this flag toggle from keySetString() to keySetBinary(). If no value (nor size) is given, it will be a NULL key.

  // Create and initialize a key with a name and nothing else
  Key *k=keyNew("user:/tmp/ex2",
          KEY_BINARY,
          KEY_SIZE, 4,               // now the size is important
          KEY_VALUE, "some data",    // sets the binary value ("some")
          KEY_END);                  // end of args

  Key *k=keyNew("user:/tmp/ex4",
          KEY_BINARY,                     // key type
          KEY_SIZE, 7,                    // assume binary length 7
          KEY_VALUE, "some data",         // value that will be truncated in 7 bytes
          KEY_META, "comment/#0", "value is truncated",
          KEY_END);                       // end of args

  Precondition

  name is a valid Key name

  Variable arguments are a valid combination

  Postcondition

  returns a new, fully initialized Key object with the valid Key name and all data given by variable arguments

  Parameters

  name	a valid name to the key (see keySetName())

  Returns

  a pointer to a new allocated and initialized Key object.

  Return values

  NULL	on allocation error or if an invalid name was passed (see keySetName()).

  Since

  1.0.0

  See also

  keyDel() for deallocating a created Key object

  keySetName() for rules about which names are considered valid