Chapter 26. sockets, Sockets – Comtrol eCos User Manual

Page 429

Chapter 26. Sockets

If a network stack is present, then the FILEIO infrastructure also provides access to the standard BSD socket calls.

The netstack table contains entries which describe the network protocol stacks that are in the system image. Each
resident stack should export an entry to this table using the

NSTAB_ENTRY()

macro.

Each table entry has the following structure:

struct cyg_nstab_entry

{

cyg_bool

valid;

// true if stack initialized

cyg_uint32

syncmode;

// synchronization protocol

char

*name;

// stack name

char

*devname;

// hardware device name

CYG_ADDRWORD

data;

// private data value

int

(*init)( cyg_nstab_entry *nste );

int

(*socket)( cyg_nstab_entry *nste, int domain, int type,

int protocol, cyg_file *file );

};

This table is analogous to a combination of the filesystem and mount tables.

The

valid

field is set

true

if the stack’s

init()

function returned successfully and the

syncmode

field contains

the

CYG_SYNCMODE_SOCK_*

bits described above.

The

name

field contains the name of the protocol stack.

The

devname

field names the device that the stack is using. This may reference a device under "/dev", or may be

a name that is only meaningful to the stack itself.

The

init()

function pointer is called during system initialization to start the protocol stack running. If it returns

non-zero the

valid

field is set false and the stack will be ignored subsequently.

The

socket()

function is called to attempt to create a socket in the stack. When the

socket()

API function is

called the netstack table is scanned and for each valid entry the

socket()

function pointer is called. If this returns

non-zero then the scan continues to the next valid stack, or terminates with an error if the end of the table is reached.

The result of a successful socket call is an initialized file object with the

f_xops

field pointing to the following

structure:

struct cyg_sock_ops

{

int (*bind)

( cyg_file *fp, const sockaddr *sa, socklen_t len );

int (*connect)

( cyg_file *fp, const sockaddr *sa, socklen_t len );

int (*accept)

( cyg_file *fp, cyg_file *new_fp,

struct sockaddr *name, socklen_t *anamelen );

int (*listen)

( cyg_file *fp, int len );

int (*getname)

( cyg_file *fp, sockaddr *sa, socklen_t *len, int peer );

int (*shutdown)

( cyg_file *fp, int flags );

int (*getsockopt)( cyg_file *fp, int level, int optname,

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