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NFSSVC(2) System Calls Manual NFSSVC(2)

nfssvcNFS services

library “libc”

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

int
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 receives 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 object 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 fields.
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 system.

Usually 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)

The nfssvc function 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.

December 30, 2006 NetBSD-7.0.1