exportfs(2) System Calls Manual exportfs(2)
NAME
exportfs - Exports an NFS file system
SYNOPSIS
#include <nfs/nfs.h>
exportfs(access, cookie, exdata)
int access;
int *cookie;
struct exportfsdata *exdata;
DESCRIPTION
The exportfs system call allows the specified local file system to be mounted remotely by an NFS client. This system call is usually
called from mountd. The system call allows access to the kernels export database. The method of access is specified by the access flag as
follows:
#define EXPORTFS_CREATE 0x01 /* create a new export record */ #define EXPORTFS_REMOVE 0x02 /* remove an old export record */
#define EXPORTFS_READ 0x03 /* read an export record */
Each entry in the export database has the following structure:
struct exportfsdata {
dev_t e_dev; /* ID of device containing the directory */
ino_t e_ino; /* File serial number */
uint_t e_gen; /* File generation number */
char e_path[MAXPATHLEN]; /* Name of the path to export */
int e_flags; /* Export flags */
uid_t e_rootmap; /* Map root to this uid (either 0 or -2) */
uid_t e_anon; /* Map anonymous users to this uid */
struct exportfsaddrlist e_rootaddrs;
/* List of hosts where root can be mapped
* to uid 0 */
struct exportfsaddrlist e_writeaddrs;
/* List of hosts allowed write access to
* read mostly export */
int e_more; /* Used in EXPORTFS_READ */ };
struct exportfsaddrlist {
unsigned naddrs;
struct sockaddr addrvec[EXMAXADDRS]; };
The e_path argument is a pointer to a null-terminated string containing the path name of the file system or directory being exported.
The e_dev, e_ino, and e_gen fields are inputs to the system call for creating an entry. They are returned when an entry is read.
Security on the exported file systems can be improved by setting the root mapped user ID in, e_rootmap and the anonymous user id in e_anon
to user id -2. Setting the rootmap field to 0 specifies that all client superusers will be mapped to 0 and thus will have the same rights
as the local superuser. Anonymous remote users are those without UNIX credentials and superusers on client systems. Setting anon to a
user id other than -2 will map all anonymous users to that uid. Use of the rootmap field overrides values in e_anon for client superusers.
Finally, to grant superuser privileges to only a select group of clients, set rootmap to -2 and use the e_rootaddrs structure to specify
the list of privileged systems.
The export permissions flags are set in e_flags for the local file system path. The following flags are the only possible flags accepted by
exportfs:
#define M_EXRDONLY /* export read-only */ #define M_EXRDMOSTLY /* export read-write to hosts in e_writeaddrs */ #define M_EXPUBLIC
/* exported for WebNFS public access */ #define M_EXPUBINDEX /* WebNFS access with index */
By default, exports are read-write. To export a filesystem or directory read-only, set the M_EXRDONLY flag. To export a filesystem or
directory read-only to most clients and read-write to a select group, set the M_EXRDMOSTLY flag and include the list of clients in
e_writeaddrs.
To export a filesystem or directory for WebNFS public access, set the M_EXPUBLIC flag. Note that only one exported filesystem can have this
flag set. By default, the filesystem is exported read-write.
The M_EXPUBINDEX flag enables the WebNFS server to look for an index.html file when given a directory name. This flag is used in conjunc-
tion with the M_EXPUBLIC flag.
The e_more field is used in conjunction with the cookie parameter to sequentially read the kernel's export database using EXPORTFS_READ.
The contents of cookie should be set to zero to read the first record. After reading the record into exdata, the system call will set
e_more to a non-zero value if there are more records to read and will update the value of cookie. If there are no more records in the data-
base, e_more will be zero after the system call completes.
The exportfs system call returns a value of 0 upon successful completion of an operation, and -1 upon failure.
ERRORS
Not superuser. Not enough memory in the system to service the request. Bad address for exdata or cookie. Access is EXPORTFS_CREATE or
EXPORTFS_REMOVE and e_path does not exist, or access is EXPORTFS_REMOVE and e_path is not an exported path, or access is EXPORTFS_READ and
there are no exportfsdata records to read. Access is EXPORTFS_CREATE and e_path is an NFS mounted directory. Only local directories can
be exported. The exdata pointer is NULL, the cookie value is negative, or the access flag is invalid.
SEE ALSO
Files: exports(4)
Daemons: mountd(8)
exportfs(2)