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><H1
><A
NAME="FILEIO-SOCKETS">Chapter 26. Sockets</H1
><P
>If a network stack is present, then the FILEIO infrastructure also
provides access to the standard BSD socket calls.</P
><P
>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
<TT
CLASS="LITERAL"
>NSTAB_ENTRY()</TT
> macro.</P
><P
>Each table entry has the following structure:</P
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><PRE
CLASS="PROGRAMLISTING"
>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 );
};</PRE
></TD
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></TABLE
><P
>This table is analogous to a combination of the filesystem and mount
tables.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>valid</I
></TT
> field is set
<TT
CLASS="LITERAL"
>true</TT
> if the stack's <TT
CLASS="FUNCTION"
>init()</TT
>
function returned successfully and the
<TT
CLASS="STRUCTFIELD"
><I
>syncmode</I
></TT
> field contains the
<TT
CLASS="LITERAL"
>CYG_SYNCMODE_SOCK_*</TT
> bits described above.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>name</I
></TT
> field contains the name of the
protocol stack.</P
><P
>The <TT
CLASS="STRUCTFIELD"
><I
>devname</I
></TT
> 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.</P
><P
>The <TT
CLASS="FUNCTION"
>init()</TT
> function pointer is called during
system initialization to start the protocol stack running. If it
returns non-zero the <TT
CLASS="STRUCTFIELD"
><I
>valid</I
></TT
> field is set
false and the stack will be ignored subsequently.</P
><P
>The <TT
CLASS="FUNCTION"
>socket()</TT
> function is called to attempt to create a socket in the
stack. When the <TT
CLASS="FUNCTION"
>socket()</TT
> API function is called the netstack table is
scanned and for each valid entry the <TT
CLASS="FUNCTION"
>socket()</TT
>
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.</P
><P
>The result of a successful socket call is an initialized file object
with the <TT
CLASS="STRUCTFIELD"
><I
>f_xops</I
></TT
> field pointing to the
following structure:</P
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><PRE
CLASS="PROGRAMLISTING"
>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,
void *optval, socklen_t *optlen);
int (*setsockopt)( cyg_file *fp, int level, int optname,
const void *optval, socklen_t optlen);
int (*sendmsg) ( cyg_file *fp, const struct msghdr *m,
int flags, ssize_t *retsize );
int (*recvmsg) ( cyg_file *fp, struct msghdr *m,
socklen_t *namelen, ssize_t *retsize );
};</PRE
></TD
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></TABLE
><P
>It should be obvious from the names of these functions which API calls
they provide support for. The <TT
CLASS="FUNCTION"
>getname()</TT
> function
pointer provides support for both <TT
CLASS="FUNCTION"
>getsockname()</TT
>
and <TT
CLASS="FUNCTION"
>getpeername()</TT
> while the
<TT
CLASS="FUNCTION"
>sendmsg()</TT
> and <TT
CLASS="FUNCTION"
>recvmsg()</TT
>
function pointers provide support for <TT
CLASS="FUNCTION"
>send()</TT
>,
<TT
CLASS="FUNCTION"
>sendto()</TT
>, <TT
CLASS="FUNCTION"
>sendmsg()</TT
>,
<TT
CLASS="FUNCTION"
>recv()</TT
>, <TT
CLASS="FUNCTION"
>recvfrom()</TT
> and
<TT
CLASS="FUNCTION"
>recvmsg()</TT
> as appropriate.</P
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