nv.9

.\"
.\" Copyright (c) 2013 The FreeBSD Foundation
.\" Copyright (c) 2013-2015 Mariusz Zaborski <oshogbo@FreeBSD.org>
.\" All rights reserved.
.\"
.\" This documentation was written by Pawel Jakub Dawidek under sponsorship
.\" the FreeBSD Foundation.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.Dd January 3, 2025
.Dt NV 9
.Os
.Sh NAME
.Nm nvlist_create ,
.Nm nvlist_destroy ,
.Nm nvlist_error ,
.Nm nvlist_set_error ,
.Nm nvlist_empty ,
.Nm nvlist_flags ,
.Nm nvlist_exists ,
.Nm nvlist_free ,
.Nm nvlist_clone ,
.Nm nvlist_dump ,
.Nm nvlist_fdump ,
.Nm nvlist_size ,
.Nm nvlist_pack ,
.Nm nvlist_unpack ,
.Nm nvlist_send ,
.Nm nvlist_recv ,
.Nm nvlist_xfer ,
.Nm nvlist_in_array ,
.Nm nvlist_next ,
.Nm nvlist_add ,
.Nm nvlist_move ,
.Nm nvlist_get ,
.Nm nvlist_take ,
.Nm nvlist_append
.Nd "library for name/value pairs"
.Sh LIBRARY
.Lb libnv
.Sh SYNOPSIS
.In sys/nv.h
.Ft "nvlist_t *"
.Fn nvlist_create "int flags"
.Ft void
.Fn nvlist_destroy "nvlist_t *nvl"
.Ft int
.Fn nvlist_error "const nvlist_t *nvl"
.Ft void
.Fn nvlist_set_error "nvlist_t *nvl" "int error"
.Ft bool
.Fn nvlist_empty "const nvlist_t *nvl"
.Ft int
.Fn nvlist_flags "const nvlist_t *nvl"
.Ft bool
.Fn nvlist_in_array "const nvlist_t *nvl"
.\"
.Ft "nvlist_t *"
.Fn nvlist_clone "const nvlist_t *nvl"
.\"
.Ft void
.Fn nvlist_dump "const nvlist_t *nvl" "int fd"
.Ft void
.Fn nvlist_fdump "const nvlist_t *nvl" "FILE *fp"
.\"
.Ft size_t
.Fn nvlist_size "const nvlist_t *nvl"
.Ft "void *"
.Fn nvlist_pack "const nvlist_t *nvl" "size_t *sizep"
.Ft "nvlist_t *"
.Fn nvlist_unpack "const void *buf" "size_t size" "int flags"
.\"
.Ft int
.Fn nvlist_send "int sock" "const nvlist_t *nvl"
.Ft "nvlist_t *"
.Fn nvlist_recv "int sock" "int flags"
.Ft "nvlist_t *"
.Fn nvlist_xfer "int sock" "nvlist_t *nvl" "int flags"
.\"
.Ft "const char *"
.Fn nvlist_next "const nvlist_t *nvl" "int *typep" "void **cookiep"
.\"
.Ft bool
.Fn nvlist_exists "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_type "const nvlist_t *nvl" "const char *name" "int type"
.Ft bool
.Fn nvlist_exists_null "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_bool "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_number "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_string "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_nvlist "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_descriptor "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_binary "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_bool_array "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_number_array "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_string_array "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_nvlist_array "const nvlist_t *nvl" "const char *name"
.Ft bool
.Fn nvlist_exists_descriptor_array "const nvlist_t *nvl" "const char *name"
.\"
.Ft void
.Fn nvlist_add_null "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_add_bool "nvlist_t *nvl" "const char *name" "bool value"
.Ft void
.Fn nvlist_add_number "nvlist_t *nvl" "const char *name" "uint64_t value"
.Ft void
.Fn nvlist_add_string "nvlist_t *nvl" "const char *name" "const char *value"
.Ft void
.Fn nvlist_add_stringf "nvlist_t *nvl" "const char *name" "const char *valuefmt" "..."
.Ft void
.Fn nvlist_add_stringv "nvlist_t *nvl" "const char *name" "const char *valuefmt" "va_list valueap"
.Ft void
.Fn nvlist_add_nvlist "nvlist_t *nvl" "const char *name" "const nvlist_t *value"
.Ft void
.Fn nvlist_add_descriptor "nvlist_t *nvl" "const char *name" "int value"
.Ft void
.Fn nvlist_add_binary "nvlist_t *nvl" "const char *name" "const void *value" "size_t size"
.Ft void
.Fn nvlist_add_bool_array "nvlist_t *nvl" "const char *name" "const bool *value" "size_t nitems"
.
.Ft void
.Fn nvlist_add_number_array "nvlist_t *nvl" "const char *name" "const uint64_t *value" "size_t nitems"
.
.Ft void
.Fn nvlist_add_string_array "nvlist_t *nvl" "const char *name" "const char * const * value" "size_t nitems"
.
.Ft void
.Fn nvlist_add_nvlist_array "nvlist_t *nvl" "const char *name" "const nvlist_t * const * value" "size_t nitems"
.
.Ft void
.Fn nvlist_add_descriptor_array "nvlist_t *nvl" "const char *name" "const int *value" "size_t nitems"
.\"
.Ft void
.Fn nvlist_move_string "nvlist_t *nvl" "const char *name" "char *value"
.Ft void
.Fn nvlist_move_nvlist "nvlist_t *nvl" "const char *name" "nvlist_t *value"
.Ft void
.Fn nvlist_move_descriptor "nvlist_t *nvl" "const char *name" "int value"
.Ft void
.Fn nvlist_move_binary "nvlist_t *nvl" "const char *name" "void *value" "size_t size"
.Ft void
.Fn nvlist_move_bool_array "nvlist_t *nvl" "const char *name" "bool *value" "size_t nitems"
.
.Ft void
.Fn nvlist_move_number_array "nvlist_t *nvl" "const char *name" "uint64_t *value" "size_t nitems"
.
.Ft void
.Fn nvlist_move_string_array "nvlist_t *nvl" "const char *name" "char **value" "size_t nitems"
.
.Ft void
.Fn nvlist_move_nvlist_array "nvlist_t *nvl" "const char *name" "nvlist_t **value" "size_t nitems"
.
.Ft void
.Fn nvlist_move_descriptor_array "nvlist_t *nvl" "const char *name" "int *value" "size_t nitems"
.\"
.Ft bool
.Fn nvlist_get_bool "const nvlist_t *nvl" "const char *name"
.Ft uint64_t
.Fn nvlist_get_number "const nvlist_t *nvl" "const char *name"
.Ft "const char *"
.Fn nvlist_get_string "const nvlist_t *nvl" "const char *name"
.Ft "const nvlist_t *"
.Fn nvlist_get_nvlist "const nvlist_t *nvl" "const char *name"
.Ft int
.Fn nvlist_get_descriptor "const nvlist_t *nvl" "const char *name"
.Ft "const void *"
.Fn nvlist_get_binary "const nvlist_t *nvl" "const char *name" "size_t *sizep"
.Ft "const bool *"
.Fn nvlist_get_bool_array "const nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "const uint64_t *"
.Fn nvlist_get_number_array "const nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "const char * const *"
.Fn nvlist_get_string_array "const nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "const nvlist_t * const *"
.Fn nvlist_get_nvlist_array "const nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "const int *"
.Fn nvlist_get_descriptor_array "const nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "const nvlist_t *"
.Fn nvlist_get_parent "const nvlist_t *nvl" "void **cookiep"
.Ft "const nvlist_t *"
.Fn nvlist_get_array_next "const nvlist_t *nvl"
.Ft "const nvlist_t *"
.Fn nvlist_get_pararr "const nvlist_t *nvl" "void **cookiep"
.\"
.Ft bool
.Fn nvlist_take_bool "nvlist_t *nvl" "const char *name"
.Ft uint64_t
.Fn nvlist_take_number "nvlist_t *nvl" "const char *name"
.Ft "char *"
.Fn nvlist_take_string "nvlist_t *nvl" "const char *name"
.Ft "nvlist_t *"
.Fn nvlist_take_nvlist "nvlist_t *nvl" "const char *name"
.Ft int
.Fn nvlist_take_descriptor "nvlist_t *nvl" "const char *name"
.Ft "void *"
.Fn nvlist_take_binary "nvlist_t *nvl" "const char *name" "size_t *sizep"
.Ft "bool *"
.Fn nvlist_take_bool_array "nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "uint64_t **"
.Fn nvlist_take_number_array "nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "char **"
.Fn nvlist_take_string_array "nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "nvlist_t **"
.Fn nvlist_take_nvlist_array "nvlist_t *nvl" "const char *name" "size_t *nitems"
.Ft "int *"
.Fn nvlist_take_descriptor_array "nvlist_t *nvl" "const char *name" "size_t *nitems"
.\"
.Ft void
.Fn nvlist_append_bool_array "nvlist_t *nvl" "const char *name" "const bool value"
.Ft void
.Fn nvlist_append_number_array "nvlist_t *nvl" "const char *name" "const uint64_t value"
.Ft void
.Fn nvlist_append_string_array "nvlist_t *nvl" "const char *name" "const char * const value"
.Ft void
.Fn nvlist_append_nvlist_array "nvlist_t *nvl" "const char *name" "const nvlist_t * const value"
.Ft void
.Fn nvlist_append_descriptor_array "nvlist_t *nvl" "const char *name" "int value"
.\"
.Ft void
.Fn nvlist_free "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_type "nvlist_t *nvl" "const char *name" "int type"
.\"
.Ft void
.Fn nvlist_free_null "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_bool "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_number "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_string "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_nvlist "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_descriptor "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_binary "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_bool_array "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_number_array "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_string_array "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_nvlist_array "nvlist_t *nvl" "const char *name"
.Ft void
.Fn nvlist_free_descriptor_array "nvlist_t *nvl" "const char *name"
.Sh DESCRIPTION
The
.Nm libnv
library permits creating and managing name value pairs as well as
sending and receiving
them over sockets.
A group (list) of name value pairs is called an
.Nm nvlist .
The API supports the following data types for values:
.Bl -ohang -offset indent
.It Sy null ( NV_TYPE_NULL )
There is no data associated with the name.
.It Sy bool ( NV_TYPE_BOOL )
The value can be either
.Dv true
or
.Dv false .
.It Sy number ( NV_TYPE_NUMBER )
The value is a number stored as
.Vt uint64_t .
.It Sy string ( NV_TYPE_STRING )
The value is a C string.
.It Sy nvlist ( NV_TYPE_NVLIST )
The value is a nested nvlist.
.It Sy descriptor ( NV_TYPE_DESCRIPTOR )
The value is a file descriptor.
Note that file descriptors can be sent only over
.Xr unix 4
domain sockets.
.It Sy binary ( NV_TYPE_BINARY )
The value is a binary buffer.
.It Sy bool array ( NV_TYPE_BOOL_ARRAY )
The value is an array of boolean values.
.It Sy number array ( NV_TYPE_NUMBER_ARRAY )
The value is an array of numbers, each stored as
.Vt uint64_t .
.It Sy string array ( NV_TYPE_STRING_ARRAY )
The value is an array of C strings.
.It Sy 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
.Fn nvlist_get_array_next
and
.Fn nvlist_get_pararr
functions.
.It Sy descriptor array ( NV_TYPE_DESCRIPTOR_ARRAY )
The value is an array of files descriptors.
.El
.Pp
The
.Fn nvlist_create
function allocates memory and initializes an nvlist.
.Pp
The following flags can be provided:
.Pp
.Bl -tag -width "NV_FLAG_IGNORE_CASE" -compact -offset indent
.It Dv NV_FLAG_IGNORE_CASE
Perform case-insensitive lookups of provided names.
.It Dv NV_FLAG_NO_UNIQUE
Names in the nvlist do not have to be unique.
.El
.Pp
The
.Fn nvlist_destroy
function destroys the given nvlist.
This function does nothing if
.Fa nvl
is
.Dv NULL .
This function never modifies
.Va errno .
.Pp
The
.Fn nvlist_error
function returns the first error set on
.Fa nvl .
If
.Fa nvl
is not in the error state,
this function returns zero.
If
.Fa nvl
is
.Dv NULL ,
.Er ENOMEM
is returned.
.Pp
The
.Fn nvlist_set_error
function sets an the error value for
.Fa nvl .
Subsequent calls to
.Fn nvlist_error
will return
.Fa error .
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.
.Pp
The
.Fn nvlist_empty
function returns
.Dv true
if
.Fa nvl
is empty and
.Dv false
otherwise.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_flags
function returns the flags used to create
.Fa nvl
with the
.Fn nvlist_create ,
.Fn nvlist_recv ,
.Fn nvlist_unpack ,
or
.Fn nvlist_xfer
functions.
.Pp
The
.Fn nvlist_in_array
function returns
.Dv true
if
.Fa nvl
is part of an array that is a member of another nvlist.
.Pp
The
.Fn nvlist_clone
function clones
.Fa nvl .
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
.Xr dup 2
system call before placing them in the clone.
.Pp
The
.Fn nvlist_dump
function dumps nvlist content for debugging purposes to the file descriptor
.Fa fd .
.Pp
The
.Fn nvlist_fdump
dumps nvlist content for debugging purposes to the file stream
.Fa fp .
.Pp
The
.Fn nvlist_size
function returns the size of the binary buffer that would be generated by the
.Fn nvlist_pack
function.
.Pp
The
.Fn nvlist_pack
function converts the given nvlist to a binary buffer.
The function allocates memory for the buffer which should be freed with the
.Xr free 3
function.
If the
.Fa sizep
argument is not
.Dv NULL ,
the size of the buffer is stored there.
This function returns
.Dv NULL
in case of an error (allocation failure).
If the nvlist contains any file descriptors
.Dv NULL
will be returned.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_unpack
function converts a binary buffer to a new nvlist.
The
.Fa flags
argument has the same meaning as the
.Fa flags
argument passed to
.Fn nvlist_create .
If
.Fa flags
do not match the flags used to create the initial nvlist before it was packed,
this function will fail.
The flags of nested nvlists are not validated by this function.
The caller is responsible for validating the flags on any nested nvlists using
.Fn nvlist_flags .
This function returns the new nvlist on success or
.Dv NULL
in case of an error.
.Pp
The
.Fn nvlist_send
function sends
.Fa nvl
over the socket
.Fa sock .
Note that nvlists that contain file descriptors can only be sent over
.Xr unix 4
domain sockets.
.Pp
The
.Fn nvlist_recv
function receives an nvlist over the socket
.Fa sock .
As with
.Fn nvlist_unpack ,
the
.Fa flags
argument is used to construct the new nvlist and must match the flags used
to construct the original nvlist written to
.Fa sock
by the peer.
The flags of nested nvlists are not validated by this function.
The caller is responsible for validating the flags on any nested nvlists using
.Fn nvlist_flags .
This function returns the new nvlist on success or
.Dv NULL
in case of an error.
.Pp
The
.Fn nvlist_xfer
function sends
.Fa nvl
over the socket
.Fa sock
argument and then receives a new nvlist over the same socket.
The
.Fa flags
argument applies to the new nvlist similar to
.Fn nvlist_recv .
The nvlist
.Fa nvl
is always destroyed.
This function returns the new nvlist on success or
.Dv NULL
in case of an error.
.Pp
The
.Fn nvlist_next
function iterates over
.Fa nvl
returning the names and types of subsequent
elements.
The
.Fa cookiep
argument determines which element is returned.
If
.Va *cookiep
is
.Dv NULL ,
the values for the first element in the list are returned.
Otherwise,
.Va *cookiep
should contain the result of a prior call to
.Fn nvlist_next
in which case values for the next element from
.Fa nvl
are returned.
This function returns
.Dv NULL
when there are no more elements on
.Fa nvl .
The
.Fa typep
argument can be
.Dv NULL .
Elements may not be removed from
.Fa nvl
the nvlist while traversing it.
.Fa nvl
must not be in the error state.
Additional actions can be performed on an element identified by a cookie
via the
.Xr cnv 9
API .
.Pp
The
.Fn nvlist_exists
function returns
.Dv true
if an element named
.Fa name
exists in
.Fa nvl
(regardless of type) or
.Dv false
otherwise.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_exists_type
function returns
.Dv true
if an element named
.Fa name
of type
.Fa type
exists or
.Dv false
otherwise.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_exists_null ,
.Fn nvlist_exists_bool ,
.Fn nvlist_exists_number ,
.Fn nvlist_exists_string ,
.Fn nvlist_exists_nvlist ,
.Fn nvlist_exists_descriptor ,
.Fn nvlist_exists_binary ,
.Fn nvlist_exists_bool_array ,
.Fn nvlist_exists_number_array ,
.Fn nvlist_exists_string_array ,
.Fn nvlist_exists_nvlist_array ,
.Fn nvlist_exists_descriptor_array
functions return
.Dv true
if element named
.Fa name
with the type determined by the function name
exists or
.Dv false
otherwise.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_add_null ,
.Fn nvlist_add_bool ,
.Fn nvlist_add_number ,
.Fn nvlist_add_string ,
.Fn nvlist_add_stringf ,
.Fn nvlist_add_stringv ,
.Fn nvlist_add_nvlist ,
.Fn nvlist_add_descriptor ,
.Fn nvlist_add_binary ,
.Fn nvlist_add_bool_array ,
.Fn nvlist_add_number_array ,
.Fn nvlist_add_string_array ,
.Fn nvlist_add_nvlist_array ,
.Fn nvlist_add_descriptor_array
functions add an element to
.Fa nvl .
When adding a string or binary buffer, these functions allocate memory
and copy the data.
When adding an nvlist, the
.Fa value
nvlist is cloned and the clone is added to
.Fa nvl .
When adding a file descriptor, the descriptor is duplicated via the
.Xr dup 2
system call and the new file descriptor is added.
The array functions fail if there are any
.Dv NULL
elements in the array, or if the array pointer is
.Dv NULL .
If an error occurs while adding a new element,
an internal error is set which can be
examined using the
.Fn nvlist_error
function.
.Pp
The
.Fn nvlist_move_string ,
.Fn nvlist_move_nvlist ,
.Fn nvlist_move_descriptor ,
.Fn nvlist_move_binary ,
.Fn nvlist_move_bool_array ,
.Fn nvlist_move_number_array ,
.Fn nvlist_move_string_array ,
.Fn nvlist_move_nvlist_array ,
.Fn nvlist_move_descriptor_array
functions add an element to
.Fa nvl ,
but unlike the
.Fn nvlist_add_<type>
functions they consume the given resource.
For string, file descriptor, binary buffer, or nvlist values,
no value should be moved into an nvlist multiple times;
doing so will cause that value to be freed multiple times.
Note that strings or binary buffers must be allocated with
.Xr malloc 3 ,
and the pointers will be released via
.Xr free 3
when
.Fa nvl
is destroyed.
The array functions fail if there are any
.Dv NULL
elements, or if the array pointer is
.Dv NULL .
If an error occurs while adding new element, the resource is destroyed and
an internal error is set which can be examined using the
.Fn nvlist_error
function.
.Pp
The
.Fn nvlist_get_bool ,
.Fn nvlist_get_number ,
.Fn nvlist_get_string ,
.Fn nvlist_get_nvlist ,
.Fn nvlist_get_descriptor ,
.Fn nvlist_get_binary ,
.Fn nvlist_get_bool_array ,
.Fn nvlist_get_number_array ,
.Fn nvlist_get_string_array ,
.Fn nvlist_get_nvlist_array ,
.Fn nvlist_get_descriptor_array
functions return the value of the first element in
.Fa nvl
named
.Fa name .
For string, nvlist, file descriptor, binary buffer, or array values,
the returned resource must not be modified - it still belongs to
.Fa nvl .
.Pp
If an element named
.Fa name
does not exist, the program aborts.
To avoid this, the caller should check for the existence of the element before
trying to obtain the value or use the
.Xr dnv 9
extension which provides a default value in the case of a missing element.
.Pp
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_get_parent
function returns the parent nvlist of
.Fa nvl .
.Pp
The
.Fn nvlist_get_array_next
function returns the next element after
.Fa nvl
from an array of nvlists.
If
.Fa nvl
is not in an array of nvlists or it is the last element,
this function returns
.Dv NULL .
An nvlist is only in an nvlist array if it was added to an nvlist array using
.Fn nvlist_add_nvlist_array ,
.Fn nvlist_append_nvlist_array ,
or
.Fn nvlist_move_nvlist_array .
.Pp
The
.Fn nvlist_get_pararr
function returns the next element after
.Fn nvl
from an array of nvlists.
If
.Fn nvl
is the last element in an array of nvlists,
the parent nvlist of
.Fa nvl is
returned.
If
.Fn nvl
is not in an array of nvlists,
.Dv NULL
is returned.
.Pp
The
.Fn nvlist_take_bool ,
.Fn nvlist_take_number ,
.Fn nvlist_take_string ,
.Fn nvlist_take_nvlist ,
.Fn nvlist_take_descriptor ,
.Fn nvlist_take_binary ,
.Fn nvlist_take_bool_array ,
.Fn nvlist_take_number_array ,
.Fn nvlist_take_string_array ,
.Fn nvlist_take_nvlist_array ,
.Fn nvlist_take_descriptor_array
functions return the value of the element named
.Fa name
and remove the element from
.Fa nvl .
For string and binary buffer values, the caller is responsible for freeing
the returned value using the
.Xr free 3
function.
For nvlist values, the caller is responsible for destroying the returned nvlist
using the
.Fn nvlist_destroy
function.
For file descriptor values, the caller is responsible for closing the
returned descriptor
using the
.Fn close 2
system call.
For array values, the caller is responsible for destroying every element of
the array based on the element type.
In addition, the caller must also free the pointer to the array using the
.Xr free 3
function.
.Pp
If an element named
.Fa name
does not exist, the program aborts.
To avoid this, the caller should check for the existence of the element before
trying to obtain the value or use the
.Xr dnv 9
extension which provides a default value in the case of a missing element.
.Pp
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_append_bool_array ,
.Fn nvlist_append_number_array ,
.Fn nvlist_append_string_array ,
.Fn nvlist_append_nvlist_array ,
.Fn nvlist_append_descriptor_array
functions append an element to an existing array using the same semantics
as the add functions (that is, the element will be copied when applicable).
If the array named
.Fa name
does not exist, then it will be created
as if using the
.Fn nvlist_add_<type>_array
function.
If an error occurs while appending a new element,
an internal error is set on
.Fa nvl .
.Pp
The
.Fn nvlist_free
function removes the first element named
.Fa name
from
.Fa nvl
(regardless of type)
and frees all resources associated with it.
If no element named
.Fa name
exists, the program aborts.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_free_type
function removes the first element named
.Fa name
of type
.Fa type
from
.Fa nvl
and frees all resources associated with it.
If no element named
.Fa name
of type
.Fa type
exists, the program aborts.
The nvlist must not be in the error state.
.Pp
The
.Fn nvlist_free_null ,
.Fn nvlist_free_bool ,
.Fn nvlist_free_number ,
.Fn nvlist_free_string ,
.Fn nvlist_free_nvlist ,
.Fn nvlist_free_descriptor ,
.Fn nvlist_free_binary ,
.Fn nvlist_free_bool_array ,
.Fn nvlist_free_number_array ,
.Fn nvlist_free_string_array ,
.Fn nvlist_free_nvlist_array ,
.Fn nvlist_free_descriptor_array
functions remove the first element named
.Fa name
with the type determined by the function name from
.Fa nvl
free all resources associated with it.
If no element named
.Fa name
with the appropriate type exists, the program aborts.
The nvlist must not be in the error state.
.Ss Notes
The
.Fn nvlist_pack
and
.Fn nvlist_unpack
functions handle byte-order conversions, so binary buffers can be
packed and unpacked on hosts with different endianness.
.Pp
The
.Fn nvlist_recv ,
.Fn nvlist_send ,
and
.Fn nvlist_xfer
functions can transfer nvlists between hosts with different endianness.
.Ss Kernel Considerations
The
.Nm nv ,
.Nm cnv ,
and
.Nm dnv
APIs can be used in the kernel with the following differences:
.Bl -bullet
.It
File descriptor and file descriptor array value types are not supported.
.It
.Fn nvlist_recv ,
.Fn nvlist_send ,
and
.Fn nvlist_xfer
are not supported.
.It
All memory allocations use the
.Dv M_NVLIST
memory type with
.Xr malloc 9
and
.Xr free 9 .
As a result, any allocated buffers moved into an nvlist must be allocated with
.Dv M_NVLIST ,
and buffers returned by functions such as
.Fn nvlist_pack
must be freed with
.Dv M_NVLIST .
.El
.Sh EXAMPLES
The following example demonstrates how to prepare an nvlist and send it over a
.Xr unix 4
domain socket.
.Bd -literal
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 is 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);
.Ed
.Pp
Receiving an nvlist and retrieving element values:
.Bd -literal
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 accept a pointer to the nvlist's internal 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 file descriptor. */
fd = nvlist_take_descriptor(nvl, "fd");

printf("command=%s filename=%s fd=%d\n", command, filename, fd);

/* command is freed by nvlist_destroy() */
nvlist_destroy(nvl);
free(filename);
close(fd);
.Ed
.Pp
Iterating over an nvlist:
.Bd -literal
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");
}
.Ed
.Pp
Iterating over every nested nvlist:
.Bd -literal
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);
.Ed
.Pp
Iterating over every nested nvlist and every nvlist element:
.Bd -literal
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");

cookie = NULL;
do {
	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;
		}
	}
} while ((nvl = nvlist_get_pararr(nvl, &cookie)) != NULL);
.Ed
.Pp
Or alternatively:
.Bd -literal
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);
.Ed
.Sh SEE ALSO
.Xr close 2 ,
.Xr dup 2 ,
.Xr open 2 ,
.Xr err 3 ,
.Xr free 3 ,
.Xr printf 3 ,
.Xr unix 4
.Sh HISTORY
The
.Nm libnv
library appeared in
.Fx 11.0 .
.Sh AUTHORS
.An -nosplit
The
.Nm libnv
library was implemented by
.An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net
under sponsorship from the FreeBSD Foundation.