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NV(9) FreeBSD Kernel Developer's Manual NV(9)
NAME
nvlist_create, nvlist_destroy, nvlist_error, nvlist_set_error,
nvlist_empty, nvlist_flags, nvlist_exists, nvlist_free, nvlist_clone,
nvlist_dump, nvlist_fdump, nvlist_size, nvlist_pack, nvlist_unpack,
nvlist_send, nvlist_recv, nvlist_xfer, nvlist_in_array, nvlist_next,
nvlist_add, nvlist_move, nvlist_get, nvlist_take, nvlist_append - library
for name/value pairs
LIBRARY
Name/value pairs library (libnv, -lnv)
SYNOPSIS
#include <sys/nv.h>
nvlist_t *
nvlist_create(int flags);
void
nvlist_destroy(nvlist_t *nvl);
int
nvlist_error(const nvlist_t *nvl);
void
nvlist_set_error(nvlist_t *nvl, int error);
bool
nvlist_empty(const nvlist_t *nvl);
int
nvlist_flags(const nvlist_t *nvl);
bool
nvlist_in_array(const nvlist_t *nvl);
nvlist_t *
nvlist_clone(const nvlist_t *nvl);
void
nvlist_dump(const nvlist_t *nvl, int fd);
void
nvlist_fdump(const nvlist_t *nvl, FILE *fp);
size_t
nvlist_size(const nvlist_t *nvl);
void *
nvlist_pack(const nvlist_t *nvl, size_t *sizep);
nvlist_t *
nvlist_unpack(const void *buf, size_t size, int flags);
int
nvlist_send(int sock, const nvlist_t *nvl);
nvlist_t *
bool
nvlist_exists(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_type(const nvlist_t *nvl, const char *name, int type);
bool
nvlist_exists_null(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_bool(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_number(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_string(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_nvlist(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_descriptor(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_binary(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_bool_array(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_number_array(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_string_array(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_nvlist_array(const nvlist_t *nvl, const char *name);
bool
nvlist_exists_descriptor_array(const nvlist_t *nvl, const char *name);
void
nvlist_add_null(nvlist_t *nvl, const char *name);
void
nvlist_add_bool(nvlist_t *nvl, const char *name, bool value);
void
nvlist_add_number(nvlist_t *nvl, const char *name, uint64_t value);
void
nvlist_add_string(nvlist_t *nvl, const char *name, const char *value);
void
nvlist_add_stringf(nvlist_t *nvl, const char *name, const char *valuefmt,
...);
void
nvlist_add_descriptor(nvlist_t *nvl, const char *name, int value);
void
nvlist_add_binary(nvlist_t *nvl, const char *name, const void *value,
size_t size);
void
nvlist_add_bool_array(nvlist_t *nvl, const char *name, const bool *value,
size_t nitems);
void
nvlist_add_number_array(nvlist_t *nvl, const char *name,
const uint64_t *value, size_t nitems);
void
nvlist_add_string_array(nvlist_t *nvl, const char *name,
const char * const * value, size_t nitems);
void
nvlist_add_nvlist_array(nvlist_t *nvl, const char *name,
const nvlist_t * const * value, size_t nitems);
void
nvlist_add_descriptor_array(nvlist_t *nvl, const char *name,
const int *value, size_t nitems);
void
nvlist_move_string(nvlist_t *nvl, const char *name, char *value);
void
nvlist_move_nvlist(nvlist_t *nvl, const char *name, nvlist_t *value);
void
nvlist_move_descriptor(nvlist_t *nvl, const char *name, int value);
void
nvlist_move_binary(nvlist_t *nvl, const char *name, void *value,
size_t size);
void
nvlist_move_bool_array(nvlist_t *nvl, const char *name, bool *value,
size_t nitems);
void
nvlist_move_number_array(nvlist_t *nvl, const char *name,
uint64_t *value, size_t nitems);
void
nvlist_move_string_array(nvlist_t *nvl, const char *name, char **value,
size_t nitems);
void
nvlist_move_nvlist_array(nvlist_t *nvl, const char *name,
nvlist_t **value, size_t nitems);
void
nvlist_move_descriptor_array(nvlist_t *nvl, const char *name, int *value,
const char *
nvlist_get_string(const nvlist_t *nvl, const char *name);
const nvlist_t *
nvlist_get_nvlist(const nvlist_t *nvl, const char *name);
int
nvlist_get_descriptor(const nvlist_t *nvl, const char *name);
const void *
nvlist_get_binary(const nvlist_t *nvl, const char *name, size_t *sizep);
const bool *
nvlist_get_bool_array(const nvlist_t *nvl, const char *name,
size_t *nitems);
const uint64_t *
nvlist_get_number_array(const nvlist_t *nvl, const char *name,
size_t *nitems);
const char * const *
nvlist_get_string_array(const nvlist_t *nvl, const char *name,
size_t *nitems);
const nvlist_t * const *
nvlist_get_nvlist_array(const nvlist_t *nvl, const char *name,
size_t *nitems);
const int *
nvlist_get_descriptor_array(const nvlist_t *nvl, const char *name,
size_t *nitems);
const nvlist_t *
nvlist_get_parent(const nvlist_t *nvl, void **cookiep);
const nvlist_t *
nvlist_get_array_next(const nvlist_t *nvl);
const nvlist_t *
nvlist_get_pararr(const nvlist_t *nvl, void **cookiep);
bool
nvlist_take_bool(nvlist_t *nvl, const char *name);
uint64_t
nvlist_take_number(nvlist_t *nvl, const char *name);
char *
nvlist_take_string(nvlist_t *nvl, const char *name);
nvlist_t *
nvlist_take_nvlist(nvlist_t *nvl, const char *name);
int
nvlist_take_descriptor(nvlist_t *nvl, const char *name);
void *
nvlist_take_binary(nvlist_t *nvl, const char *name, size_t *sizep);
char **
nvlist_take_string_array(nvlist_t *nvl, const char *name,
size_t *nitems);
nvlist_t **
nvlist_take_nvlist_array(nvlist_t *nvl, const char *name,
size_t *nitems);
int *
nvlist_take_descriptor_array(nvlist_t *nvl, const char *name,
size_t *nitems);
void
nvlist_append_bool_array(nvlist_t *nvl, const char *name,
const bool value);
void
nvlist_append_number_array(nvlist_t *nvl, const char *name,
const uint64_t value);
void
nvlist_append_string_array(nvlist_t *nvl, const char *name,
const char * const value);
void
nvlist_append_nvlist_array(nvlist_t *nvl, const char *name,
const nvlist_t * const value);
void
nvlist_append_descriptor_array(nvlist_t *nvl, const char *name,
int value);
void
nvlist_free(nvlist_t *nvl, const char *name);
void
nvlist_free_type(nvlist_t *nvl, const char *name, int type);
void
nvlist_free_null(nvlist_t *nvl, const char *name);
void
nvlist_free_bool(nvlist_t *nvl, const char *name);
void
nvlist_free_number(nvlist_t *nvl, const char *name);
void
nvlist_free_string(nvlist_t *nvl, const char *name);
void
nvlist_free_nvlist(nvlist_t *nvl, const char *name);
void
nvlist_free_descriptor(nvlist_t *nvl, const char *name);
void
nvlist_free_binary(nvlist_t *nvl, const char *name);
void
nvlist_free_string_array(nvlist_t *nvl, const char *name);
void
nvlist_free_nvlist_array(nvlist_t *nvl, const char *name);
void
nvlist_free_descriptor_array(nvlist_t *nvl, const char *name);
DESCRIPTION
The libnv library allows to easily manage name value pairs as well as
send and receive them over sockets. A group (list) of name value pairs
is called an nvlist. The API supports the following data types:
null (NV_TYPE_NULL)
There is no data associated with the name.
bool (NV_TYPE_BOOL)
The value can be either true or false.
number (NV_TYPE_NUMBER)
The value is a number stored as uint64_t.
string (NV_TYPE_STRING)
The value is a C string.
nvlist (NV_TYPE_NVLIST)
The value is a nested nvlist.
descriptor (NV_TYPE_DESCRIPTOR)
The value is a file descriptor. Note that file descriptors can be
sent only over unix(4) domain sockets.
binary (NV_TYPE_BINARY)
The value is a binary buffer.
bool array (NV_TYPE_BOOL_ARRAY)
The value is an array of boolean values.
number array (NV_TYPE_NUMBER_ARRAY)
The value is an array of numbers, each stored as uint64_t.
string array (NV_TYPE_STRING_ARRAY)
The value is an array of C strings.
nvlist array (NV_TYPE_NVLIST_ARRAY)
The value is an array of nvlists. When an nvlist is added to an
array, it becomes part of the primary nvlist. Traversing these
arrays can be done using the nvlist_get_array_next() and
nvlist_get_pararr() functions.
descriptor array (NV_TYPE_DESCRIPTOR_ARRAY)
The value is an array of files descriptors.
The nvlist_create() function allocates memory and initializes an nvlist.
The following flag can be provided:
NV_FLAG_IGNORE_CASE Perform case-insensitive lookups of provided
The nvlist_error() function returns any error value that the nvlist
accumulated. If the given nvlist is NULL the ENOMEM error will be
returned.
The nvlist_set_error() function sets an nvlist to be in the error state.
Subsequent calls to nvlist_error() will return the given error value.
This function cannot be used to clear the error state from an nvlist.
This function does nothing if the nvlist is already in the error state.
The nvlist_empty() function returns true if the given nvlist is empty and
false otherwise. The nvlist must not be in error state.
The nvlist_flags() function returns flags used to create the nvlist with
the nvlist_create() function.
The nvlist_in_array() function returns true if nvl is part of an array
that is a member of another nvlist.
The nvlist_clone() functions clones the given nvlist. The clone shares
no resources with its origin. This also means that all file descriptors
that are part of the nvlist will be duplicated with the dup(2) system
call before placing them in the clone.
The nvlist_dump() dumps nvlist content for debugging purposes to the
given file descriptor fd.
The nvlist_fdump() dumps nvlist content for debugging purposes to the
given file stream fp.
The nvlist_size() function returns the size of the given nvlist after
converting it to binary buffer with the nvlist_pack() function.
The nvlist_pack() function converts the given nvlist to a binary buffer.
The function allocates memory for the buffer, which should be freed with
the free(3) function. If the sizep argument is not NULL, the size of the
buffer will be stored there. The function returns NULL in case of an
error (allocation failure). If the nvlist contains any file descriptors
NULL will be returned. The nvlist must not be in error state.
The nvlist_unpack() function converts the given buffer to the nvlist.
The flags argument defines what type of the top level nvlist is expected
to be. Flags are set up using the nvlist_create() function. If the
nvlist flags do not match the flags passed to nvlist_unpack(), the nvlist
will not be returned. Every nested nvlist list should be checked using
nvlist_flags() function. The function returns NULL in case of an error.
The nvlist_send() function sends the given nvlist over the socket given
by the sock argument. Note that nvlist that contains file descriptors
can only be send over unix(4) domain sockets.
The nvlist_recv() function receives nvlist over the socket given by the
sock argument. The flags argument defines what type of the top level
nvlist is expected to be. Flags are set up using the nvlist_create()
function. If the nvlist flags do not match the flags passed to
nvlist_recv(), the nvlist will not be returned. Every nested nvlist list
should be checked using nvlist_flags() function.
The nvlist_xfer() function sends the given nvlist over the socket given
by the sock argument and receives nvlist over the same socket. The flags
and types of subsequent elements. The cookiep argument allows the
function to figure out which element should be returned next. The
*cookiep should be set to NULL for the first call and should not be
changed later. Returning NULL means there are no more elements on the
nvlist. The typep argument can be NULL. Elements may not be removed
from the nvlist while traversing it. The nvlist must not be in error
state. Note that nvlist_next() will handle cookiep being set to NULL.
In this case first element is returned or NULL if nvlist is empty. This
behavior simplifies removing the first element from the list.
The nvlist_exists() function returns true if element of the given name
exists (besides of its type) or false otherwise. The nvlist must not be
in error state.
The nvlist_exists_type() function returns true if element of the given
name and the given type exists or false otherwise. The nvlist must not
be in error state.
The nvlist_exists_null(), nvlist_exists_bool(), nvlist_exists_number(),
nvlist_exists_string(), nvlist_exists_nvlist(),
nvlist_exists_descriptor(), nvlist_exists_binary(),
nvlist_exists_bool_array(), nvlist_exists_number_array(),
nvlist_exists_string_array(), nvlist_exists_nvlist_array(),
nvlist_exists_descriptor_array() functions return true if element of the
given name and the given type determined by the function name exists or
false otherwise. The nvlist must not be in error state.
The nvlist_add_null(), nvlist_add_bool(), nvlist_add_number(),
nvlist_add_string(), nvlist_add_stringf(), nvlist_add_stringv(),
nvlist_add_nvlist(), nvlist_add_descriptor(), nvlist_add_binary(),
nvlist_add_bool_array(), nvlist_add_number_array(),
nvlist_add_string_array(), nvlist_add_nvlist_array(),
nvlist_add_descriptor_array() functions add element to the given nvlist.
When adding string or binary buffer the functions will allocate memory
and copy the data over. When adding nvlist, the nvlist will be cloned
and clone will be added. When adding descriptor, the descriptor will be
duplicated using the dup(2) system call and the new descriptor will be
added. The array functions will fail if there are any NULL elements in
the array, or if the array pointer is NULL. If an error occurs while
adding new element, internal error is set which can be examined using the
nvlist_error() function.
The nvlist_move_string(), nvlist_move_nvlist(), nvlist_move_descriptor(),
nvlist_move_binary(), nvlist_move_bool_array(),
nvlist_move_number_array(), nvlist_move_string_array(),
nvlist_move_nvlist_array(), nvlist_move_descriptor_array() functions add
new element to the given nvlist, but unlike nvlist_add_<type>() functions
they will consume the given resource. In the case of strings,
descriptors, or nvlists every elements must be unique, or it could cause
a double free. The array functions will fail if there are any NULL
elements, or if the array pointer is NULL. If an error occurs while
adding new element, the resource is destroyed and internal error is set
which can be examined using the nvlist_error() function.
The nvlist_get_bool(), nvlist_get_number(), nvlist_get_string(),
nvlist_get_nvlist(), nvlist_get_descriptor(), nvlist_get_binary(),
nvlist_get_bool_array(), nvlist_get_number_array(),
nvlist_get_string_array(), nvlist_get_nvlist_array(),
nvlist_get_descriptor_array() functions return the value that corresponds
The nvlist_get_parent() function returns the parent nvlist of the nested
nvlist.
The nvlist_get_array_next() function returns the next element from the
array or NULL if the nvlist is not in array or it is the last element.
Note that nvlist_get_array_next() only works if you added the nvlist
array using the nvlist_move_nvlist_array() or nvlist_add_nvlist_array()
functions.
The nvlist_get_pararr() function returns the next element in the array,
or if not available the parent of the nested nvlist.
The nvlist_take_bool(), nvlist_take_number(), nvlist_take_string(),
nvlist_take_nvlist(), nvlist_take_descriptor(), nvlist_take_binary(),
nvlist_take_bool_array(), nvlist_take_number_array(),
nvlist_take_string_array(), nvlist_take_nvlist_array(),
nvlist_take_descriptor_array() functions return value associated with the
given name and remove the element from the nvlist. In case of string and
binary values, the caller is responsible for free returned memory using
the free(3) function. In case of nvlist, the caller is responsible for
destroying returned nvlist using the nvlist_destroy() function. In case
of descriptor, the caller is responsible for closing returned descriptor
using the close(2) system call. If an element of the given name does not
exist, the program will be aborted. To avoid that the caller should
check for the existence of the given name before trying to obtain the
value, or use the dnvlist(3) extension, which can provide a default value
in the case of a missing element. In the case of an array of strings or
binary values, the caller is responsible for freeing every element of the
array using the free(3) function. In the case of an array of nvlists,
the caller is responsible for destroying every element of array using the
nvlist_destroy() function. In the case of descriptors, the caller is
responsible for closing every element of array using the close(2) system
call. In every case involving an array, the caller must also free the
pointer to the array using the free(3) function. The nvlist must not be
in error state.
The nvlist_append_bool_array(), nvlist_append_number_array(),
nvlist_append_string_array(), nvlist_append_nvlist_array(),
nvlist_append_descriptor_array() functions append an element to the
existing array using the same semantics as the add functions (i.e. the
element will be copied when applicable). If the array for a given key
does not exist, then it will be created as if using the
nvlist_add_<type>_array() function. The internal error is set on append
failure.
The nvlist_free() function removes element of the given name from the
nvlist (besides of its type) and frees all resources associated with it.
If element of the given name does not exist, the program will be aborted.
The nvlist must not be in error state.
The nvlist_free_type() function removes element of the given name and the
given type from the nvlist and frees all resources associated with it.
If element of the given name and the given type does not exist, the
program will be aborted. The nvlist must not be in error state.
The nvlist_free_null(), nvlist_free_bool(), nvlist_free_number(),
nvlist_free_string(), nvlist_free_nvlist(), nvlist_free_descriptor(),
nvlist_free_binary(), nvlist_free_bool_array(),
NOTES
The nvlist_pack() and nvlist_unpack() functions handle the byte-order
conversions, so the binary buffer can be packed/unpacked by the hosts
with the different endianness.
EXAMPLES
The following example demonstrates how to prepare an nvlist and send it
over unix(4) domain socket.
nvlist_t *nvl;
int fd;
fd = open("/tmp/foo", O_RDONLY);
if (fd < 0)
err(1, "open(\"/tmp/foo\") failed");
nvl = nvlist_create(0);
/*
* There is no need to check if nvlist_create() succeeded,
* as the nvlist_add_<type>() functions can cope.
* If it failed, nvlist_send() will fail.
*/
nvlist_add_string(nvl, "filename", "/tmp/foo");
nvlist_add_number(nvl, "flags", O_RDONLY);
/*
* We just want to send the descriptor, so we can give it
* for the nvlist to consume (that's why we use nvlist_move
* not nvlist_add).
*/
nvlist_move_descriptor(nvl, "fd", fd);
if (nvlist_send(sock, nvl) < 0) {
nvlist_destroy(nvl);
err(1, "nvlist_send() failed");
}
nvlist_destroy(nvl);
Receiving nvlist and getting data:
nvlist_t *nvl;
const char *command;
char *filename;
int fd;
nvl = nvlist_recv(sock, 0);
if (nvl == NULL)
err(1, "nvlist_recv() failed");
/* For command we take pointer to nvlist's buffer. */
command = nvlist_get_string(nvl, "command");
/*
* For filename we remove it from the nvlist and take
* ownership of the buffer.
*/
filename = nvlist_take_string(nvl, "filename");
/* The same for the descriptor. */
fd = nvlist_take_descriptor(nvl, "fd");
printf("command=%s filename=%s fd=%d0, command, filename, fd);
nvlist_t *nvl;
const char *name;
void *cookie;
int type;
nvl = nvlist_recv(sock, 0);
if (nvl == NULL)
err(1, "nvlist_recv() failed");
cookie = NULL;
while ((name = nvlist_next(nvl, &type, &cookie)) != NULL) {
printf("%s=", name);
switch (type) {
case NV_TYPE_NUMBER:
printf("%ju", (uintmax_t)nvlist_get_number(nvl, name));
break;
case NV_TYPE_STRING:
printf("%s", nvlist_get_string(nvl, name));
break;
default:
printf("N/A");
break;
}
printf("\n");
}
Iterating over every nested nvlist:
nvlist_t *nvl;
const char *name;
void *cookie;
int type;
nvl = nvlist_recv(sock, 0);
if (nvl == NULL)
err(1, "nvlist_recv() failed");
cookie = NULL;
do {
while ((name = nvlist_next(nvl, &type, &cookie)) != NULL) {
if (type == NV_TYPE_NVLIST) {
nvl = nvlist_get_nvlist(nvl, name);
cookie = NULL;
}
}
} while ((nvl = nvlist_get_parent(nvl, &cookie)) != NULL);
Iterating over every nested nvlist and every nvlist element:
nvlist_t *nvl;
const nvlist_t * const *array;
const char *name;
void *cookie;
int type;
nvl = nvlist_recv(sock, 0);
if (nvl == null)
err(1, "nvlist_recv() failed");
nvl = nvlist_get_nvlist_array(nvl, name, NULL)[0];
cookie = NULL;
}
}
} while ((nvl = nvlist_get_pararr(nvl, &cookie)) != NULL);
Or alternatively:
nvlist_t *nvl, *tmp;
const nvlist_t * const *array;
const char *name;
void *cookie;
int type;
nvl = nvlist_recv(sock, 0);
if (nvl == null)
err(1, "nvlist_recv() failed");
cooke = NULL;
tmp = nvl;
do {
do {
nvl = tmp;
while ((name = nvlist_next(nvl, &type, &cookie)) != NULL) {
if (type == NV_TYPE_NVLIST) {
nvl = nvlist_get_nvlist(nvl, name);
cookie = NULL;
} else if (type == NV_TYPE_NVLIST_ARRAY) {
nvl = nvlist_get_nvlist_array(nvl, name,
NULL)[0];
cookie = NULL;
}
}
cookie = NULL;
} while ((tmp = nvlist_get_array_next(nvl)) != NULL);
} while ((tmp = nvlist_get_parent(nvl, &cookie)) != NULL);
SEE ALSO
close(2), dup(2), open(2), err(3), free(3), printf(3), unix(4)
HISTORY
The libnv library appeared in FreeBSD 11.0.
AUTHORS
The libnv library was implemented by Pawel Jakub Dawidek
<pawel@dawidek.net> under sponsorship from the FreeBSD Foundation.
FreeBSD 14.0-RELEASE-p11 February 2, 2023 FreeBSD 14.0-RELEASE-p11