nvlist_get_string (9)

Leading comments

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....

(The comments found at the beginning of the groff file "man9/nvlist_get_string.9freebsd".)

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 - library for name/value pairs

LIBRARY

Lb libnv

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 const nvlist_t *nvl const char *name size_t *nitems Ft const char * const * Fn nvlist_get_string const nvlist_t *nvl const char *name size_t *nitems Ft const nvlist_t * const * Fn nvlist_get_nvlist 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 nvlist_t *nvl const char *name size_t *nitems Ft char ** Fn nvlist_take_string nvlist_t *nvl const char *name size_t *nitems Ft nvlist_t ** Fn nvlist_take_nvlist nvlist_t *nvl const char *name size_t *nitems Ft int * Fn nvlist_take_descriptor nvlist_t *nvl const char *name size_t *nitems 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

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 Vt 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 Vt 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 Fn nvlist_get_array_next and Fn nvlist_get_pararr functions.

descriptor array ( NV_TYPE_DESCRIPTOR_ARRAY

The value is an array of files descriptors.

The Fn 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 names.

NV_FLAG_NO_UNIQUE

Names in the nvlist do not have to be unique.

The Fn nvlist_destroy function destroys the given nvlist. Function does nothing if NULL nvlist is provided. Function never modifies the errno global variable.

The Fn nvlist_error function returns any error value that the nvlist accumulated. If the given nvlist is NULL the Er ENOMEM error will be returned.

The Fn nvlist_set_error function sets an nvlist to be in the error state. Subsequent calls to Fn 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 Fn nvlist_empty function returns true if the given nvlist is empty and false otherwise. The nvlist must not be in error state.

The Fn nvlist_flags function returns flags used to create the nvlist with the Fn nvlist_create function.

The Fn nvlist_in_array function returns true if Fa nvl is part of an array that is a member of another nvlist.

The Fn 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 Fn nvlist_dump dumps nvlist content for debugging purposes to the given file descriptor Fa fd .

The Fn nvlist_fdump dumps nvlist content for debugging purposes to the given file stream Fa fp .

The Fn nvlist_size function returns the size of the given nvlist after converting it to binary buffer with the Fn nvlist_pack function.

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 free(3) function. If the Fa 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 Fn nvlist_unpack function converts the given buffer to the nvlist. The Fa flags argument defines what type of the top level nvlist is expected to be. Flags are set up using the Fn nvlist_create function. If the nvlist flags do not match the flags passed to Fn nvlist_unpack , the nvlist will not be returned. Every nested nvlist list should be checked using Fn nvlist_flags function. The function returns NULL in case of an error.

The Fn nvlist_send function sends the given nvlist over the socket given by the Fa sock argument. Note that nvlist that contains file descriptors can only be send over unix(4) domain sockets.

The Fn nvlist_recv function receives nvlist over the socket given by the Fa sock argument. The Fa flags argument defines what type of the top level nvlist is expected to be. Flags are set up using the Fn nvlist_create function. If the nvlist flags do not match the flags passed to Fn nvlist_recv , the nvlist will not be returned. Every nested nvlist list should be checked using Fn nvlist_flags function.

The Fn nvlist_xfer function sends the given nvlist over the socket given by the Fa sock argument and receives nvlist over the same socket. The Fa flags argument defines what type of the top level nvlist is expected to be. Flags are set up using the Fn nvlist_create function. If the nvlist flags do not match the flags passed to Fn nvlist_xfer , the nvlist will not be returned. Every nested nvlist list should be checked using Fn nvlist_flags function. The given nvlist is always destroyed.

The Fn nvlist_next function iterates over the given nvlist returning names and types of subsequent elements. The Fa 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 Fa 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 Fn 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 Fn 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 Fn 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 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 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 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 element to the given nvlist. When adding string or binary buffor 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 Fn nvlist_error function.

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 new element to the given nvlist, but unlike Fn 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 Fn nvlist_error function.

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 that corresponds to the given key name. In the case of strings, nvlists, descriptors, binary, or arrays, the returned resource should not be modified - they still belong to the nvlist. If an element of the given name does not exist, the program will be aborted. To avoid this, the caller should check for the existence of the 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. The nvlist must not be in error state.

The Fn nvlist_get_parent function returns the parent nvlist of the nested nvlist.

The Fn 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 Fn nvlist_get_array_next only works if you added the nvlist array using the Fn nvlist_move_nvlist_array or Fn nvlist_add_nvlist_array functions.

The Fn nvlist_get_pararr function returns the next element in the array, or if not available the parent of the nested nvlist.

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 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 Fn nvlist_destroy function. In case of descriptor, the caller is responsible for closing returned descriptor using the Fn 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 Fn nvlist_destroy function. In the case of descriptors, the caller is responsible for closing every element of array using the Fn 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 Fn 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 Fn 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 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 element of the given name and the given type determined by the function name from the nvlist and free 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.

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=%d, command, filename, fd);

nvlist_destroy(nvl);
free(filename);
close(fd);
/* command was freed by nvlist_destroy() */

Iterating over 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;
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");

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);

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 Fx 11.0 .

AUTHORS

An -nosplit The libnv library was implemented by An Pawel Jakub Dawidek Aq Mt pawel@dawidek.net under sponsorship from the FreeBSD Foundation.