freebsd-nq/lib/libnv/nv.3

.\"
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.\" This documentation was written by Pawel Jakub Dawidek under sponsorship
.\" the FreeBSD Foundation.
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.Dd January 30, 2015
.Dt NV 3
.Os
.Sh NAME
.Nm nvlist_create ,
.Nm nvlist_destroy ,
.Nm nvlist_error ,
.Nm nvlist_empty ,
.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_next ,
.Nm nvlist_add ,
.Nm nvlist_move ,
.Nm nvlist_get ,
.Nm nvlist_take
.Nd "library for name/value pairs"
.Sh LIBRARY
.Lb libnv
.Sh SYNOPSIS
.In 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 bool
.Fn nvlist_empty "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"
.\"
.Ft int
.Fn nvlist_send "int sock" "const nvlist_t *nvl"
.Ft "nvlist_t *"
.Fn nvlist_recv "int sock"
.Ft "nvlist_t *"
.Fn nvlist_xfer "int sock" "nvlist_t *nvl"
.\"
.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 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_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 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 nvlist_t *"
.Fn nvlist_get_parent "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 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"
.Sh DESCRIPTION
The
.Nm 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
.Nm nvlist .
The API supports the following data types:
.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.
.El
.Pp
The
.Fn nvlist_create
function allocates memory and initializes an nvlist.
.Pp
The following flag 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.
.El
.Pp
The
.Fn nvlist_destroy
function destroys the given nvlist.
Function does nothing if
.Dv NULL
nvlist is provided.
Function never modifies the
.Va errno
global variable.
.Pp
The
.Fn nvlist_error
function returns any error value that the nvlist accumulated.
If the given nvlist is
.Dv NULL
the
.Er ENOMEM
error will be returned.
.Pp
The
.Fn nvlist_empty
functions returns
.Dv true
if the given nvlist is empty and
.Dv false
otherwise.
The nvlist must not be in error state.
.Pp
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
.Xr dup 2
system call before placing them in the clone.
.Pp
The
.Fn nvlist_dump
dumps nvlist content for debugging purposes to the given file descriptor
.Fa fd .
.Pp
The
.Fn nvlist_fdump
dumps nvlist content for debugging purposes to the given file stream
.Fa fp .
.Pp
The
.Fn nvlist_size
function returns the size of the given nvlist after converting it to binary
buffer with 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 will be stored there.
The 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 error state.
.Pp
The
.Fn nvlist_unpack
function converts the given buffer to the nvlist.
The function returns
.Dv NULL
in case of an error.
.Pp
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
.Xr unix 4
domain sockets.
.Pp
The
.Fn nvlist_recv
function receives nvlist over the socket given by the
.Fa sock
argument.
.Pp
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 given nvlist is always destroyed.
.Pp
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
.Va *cookiep
should be set to
.Dv NULL
for the first call and should not be changed later.
Returning
.Dv 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.
.Pp
The
.Fn nvlist_exists
function returns
.Dv true
if element of the given name exists (besides of its type) or
.Dv false
otherwise.
The nvlist must not be in error state.
.Pp
The
.Fn nvlist_exists_type
function returns
.Dv true
if element of the given name and the given type exists or
.Dv false
otherwise.
The nvlist must not be in 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
functions return
.Dv true
if element of the given name and the given type determined by the function name
exists or
.Dv false
otherwise.
The nvlist must not be in 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
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
.Xr dup 2
system call and the new descriptor will be added.
If an error occurs while adding new element, 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
functions add new element to the given nvlist, but unlike
.Fn nvlist_add_<type>
functions they will consume the given resource.
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.
.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
functions allow to obtain value of the given name.
In case of string, nvlist, descriptor or binary, returned resource should
not be modified - it still belongs to the nvlist.
If element of the given name does not exist, the program will be aborted.
To avoid that the caller should check for existence before trying to obtain
the value or use
.Xr dnvlist 3
extension, which allows to provide default value for a missing element.
The nvlist must not be in error state.
.Pp
The
.Fn nvlist_get_parent
function allows to obtain the parent nvlist from the nested nvlist.
.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
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
.Xr 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 element of the given name does not exist, the program will be aborted.
To avoid that the caller should check for existence before trying to obtain
the value or use
.Xr dnvlist 3
extension, which allows to provide default value for a missing element.
The nvlist must not be in error state.
.Pp
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.
.Pp
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.
.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
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.
.Sh EXAMPLES
The following example demonstrates how to prepare an nvlist and send it over
.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'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);
.Ed
.Pp
Receiving nvlist and getting data:
.Bd -literal
nvlist_t *nvl;
const char *command;
char *filename;
int fd;

nvl = nvlist_recv(sock);
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\n", command, filename, fd);

nvlist_destroy(nvl);
free(filename);
close(fd);
/* command was freed by nvlist_destroy() */
.Ed
.Pp
Iterating over nvlist:
.Bd -literal
nvlist_t *nvl;
const char *name;
void *cookie;
int type;

nvl = nvlist_recv(sock);
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);
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
.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.