NFSSVC(2) BSD System Calls Manual NFSSVC(2)NAMEnfssvc — NFS services
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
#include <nfs/nfs.h>
int
nfssvc(int flags, void *argstructp);
DESCRIPTION
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 sys‐
tem.
RETURN VALUES
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.
ERRORS
[ENEEDAUTH] This special error value is really used for authenti‐
cation support, particularly Kerberos, as explained
above.
[EPERM] The caller is not the super-user.
SEE ALSOmount_nfs(8), nfsd(8)HISTORY
The nfssvc function first appeared in 4.4BSD.
BUGS
The nfssvc system call is designed specifically for the NFS support dae‐
mons 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 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
