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+<!-- Copyright (C) 2003 Red Hat, Inc. -->
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+><TITLE
+>Sockets</TITLE
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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
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><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
+></TR
+></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
+><TABLE
+BORDER="5"
+BGCOLOR="#E0E0F0"
+WIDTH="70%"
+><TR
+><TD
+><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
+></TR
+></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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