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NFSSVC(2) System Calls Manual NFSSVC(2)


nfssvcNFS services


Standard C Library (libc, -lc)


#include <sys/param.h>
#include <sys/mount.h>
#include <sys/time.h>
#include <nfs/rpcv2.h>
#include <nfsserver/nfs.h>
#include <unistd.h>
nfssvc(int flags, void *argstructp);


The nfssvc() system call 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.
On the client side, nfsiod(8) calls nfssvc() with the flags argument set to NFSSVC_BIOD and argstructp set to NULL to enter the kernel as a block I/O server daemon. For NQNFS, mount_nfs(8) calls nfssvc() with the NFSSVC_MNTD flag, optionally or'd with the flags NFSSVC_GOTAUTH and NFSSVC_AUTHINFAIL along with a pointer to a
struct nfsd_cargs { 
	char		*ncd_dirp;	/* Mount dir path */ 
	uid_t		ncd_authuid;	/* Effective uid */ 
	int		ncd_authtype;	/* Type of authenticator */ 
	int		ncd_authlen;	/* Length of authenticator string */ 
	u_char		*ncd_authstr;	/* Authenticator string */ 
	int		ncd_verflen;	/* and the verifier */ 
	u_char		*ncd_verfstr; 
	NFSKERBKEY_T	ncd_key;	/* Session key */ 
structure. The initial call has only the NFSSVC_MNTD flag set to specify service for the mount point. If the mount point is using Kerberos, then the mount_nfs(8) utility will return from nfssvc() with errno == ENEEDAUTH whenever the client side requires an ``rcmd'' authentication ticket for the user. The mount_nfs(8) utility will attempt to get the Kerberos ticket, and if successful will call nfssvc() with the flags NFSSVC_MNTD and NFSSVC_GOTAUTH after filling the ticket into the ncd_authstr field and setting the ncd_authlen and ncd_authtype fields of the nfsd_cargs structure. If mount_nfs(8) failed to get the ticket, nfssvc() will be called with the flags NFSSVC_MNTD, NFSSVC_GOTAUTH and NFSSVC_AUTHINFAIL to denote a failed authentication attempt.
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_int32_t	nsd_haddr;	/* Ip address of client */ 
	struct ucred	nsd_cr;		/* Cred. uid maps to */ 
	int		nsd_authlen;	/* Length of auth string (ret) */ 
	u_char		*nsd_authstr;	/* Auth string (ret) */ 
	int		nsd_verflen;	/* and the verifier */ 
	u_char		*nsd_verfstr; 
	struct timeval	nsd_timestamp;	/* timestamp from verifier */ 
	u_int32_t	nsd_ttl;	/* credential ttl (sec) */ 
	NFSKERBKEY_T	nsd_key;	/* Session key */ 
to enter the kernel as an nfsd(8) daemon. Whenever an nfsd(8) daemon receives a Kerberos authentication ticket, it will return from nfssvc() with errno == ENEEDAUTH. The nfsd(8) utility 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) utility 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.


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


This special error value is really used for authentication support, particularly Kerberos, as explained above.
The caller is not the super-user.


mount_nfs(8), nfsd(8), nfsiod(8)


The nfssvc() system call first appeared in 4.4BSD.


The nfssvc() system call is designed specifically for the NFS support daemons and as such is specific to their requirements. It should really return values to indicate the need for authentication support, since ENEEDAUTH is not really an error. Several fields of the argument structures are assumed to be valid and sometimes to be unchanged from a previous call, such that nfssvc() must be used with extreme care.
June 9, 1993 Debian