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NFSSVC(2)		    BSD	System Calls Manual		     NFSSVC(2)

     nfssvc -- NFS services

     Standard C	Library	(libc, -lc)

     #include <unistd.h>
     #include <nfs/nfs.h>

     nfssvc(int	flags, void *argstructp);

     The nfssvc() function is used by the NFS daemons to pass information into
     and out of	the kernel and also to enter the kernel	as a server daemon.
     The flags argument	consists of several bits that show what	action is to
     be	taken once in the kernel and the argstructp points to one of three
     structures	depending on which bits	are set	in flags.

   Calls used by nfsd(8)
     On	the server side, nfssvc() is called with the flag NFSSVC_NFSD and a
     pointer to	a

     struct nfsd_srvargs {
	     struct nfsd     *nsd_nfsd;	     /*	Pointer	to in kernel nfsd struct */
	     uid_t	     nsd_uid;	     /*	Effective uid mapped to	cred */
	     u_long	     nsd_haddr;	     /*	Ip address of client */
	     struct ucred    nsd_cr;	     /*	Cred. uid maps to */
	     int	     nsd_authlen;    /*	Length of auth string (ret) */
	     char	     *nsd_authstr;   /*	Auth string (ret) */

     to	enter the kernel as an nfsd(8) daemon.	Whenever an nfsd(8) daemon re-
     ceives a Kerberos authentication ticket, it will return from nfssvc()
     with errno	set to ENEEDAUTH.  The nfsd(8) will attempt to authenticate
     the ticket	and generate a set of credentials on the server	for the	"user
     id" specified in the field	nsd_uid.  This is done by first	authenticating
     the Kerberos ticket and then mapping the Kerberos principal to a local
     name and getting a	set of credentials for that user via getpwnam(3) and
     getgrouplist(3).  If successful, the nfsd(8) will call nfssvc() with the
     NFSSVC_NFSD and NFSSVC_AUTHIN flags set to	pass the credential mapping in
     nsd_cr into the kernel to be cached on the	server socket for that client.
     If	the authentication failed, nfsd(8) calls nfssvc() with the flags
     NFSSVC_NFSD and NFSSVC_AUTHINFAIL to denote an authentication failure.

     The master	nfsd(8)	server daemon calls nfssvc() with the flag
     NFSSVC_ADDSOCK and	a pointer to a

     struct nfsd_args {
	     int     sock;	     /*	Socket to serve	*/
	     caddr_t name;	     /*	Client address for connection based sockets */
	     int     namelen;	     /*	Length of name */

     to	pass a server side NFS socket into the kernel for servicing by the
     nfsd(8) daemons.

   Calls used by mountd(8)
     The mountd(8) server daemon calls nfssvc()	with the flag
     NFSSVC_SETEXPORTSLIST and a pointer to a struct mountd_exports_list ob-
     ject to atomically	change the exports lists of a specific file system.
     This structure has	the following fields:

     const char	*mel_path  Path	to the file system that	will have its exports
			   list	replaced by the	one described in the other

     size_t mel_nexports   Number of valid entries in the mel_export field.
			   If zero, the	exports	list will be cleared for the
			   given file system.

     struct export_args	mel_export[AF_MAX]
			   Set of exports to be	used for the given file	sys-

     Usually nfssvc does not return unless the server is terminated by a sig-
     nal when a	value of 0 is returned.	 Otherwise, -1 is returned and the
     global variable errno is set to specify the error.

     [ENEEDAUTH]	This special error value is really used	for authenti-
			cation support,	particularly Kerberos, as explained

     [EPERM]		The caller is not the super-user.

     mount_nfs(8), nfsd(8)

     The nfssvc	function first appeared	in 4.4BSD.

     The nfssvc	system call is designed	specifically for the NFS support dae-
     mons and as such is specific to their requirements.  It should really re-
     turn values to indicate the need for authentication support, since
     ENEEDAUTH is not really an	error.	Several	fields of the argument struc-
     tures are assumed to be valid and sometimes to be unchanged from a	previ-
     ous call, such that nfssvc	must be	used with extreme care.

BSD			       December	30, 2006			   BSD


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