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exportfs(2)
NAME
exportfs - Export an NFS file system
SYNOPSIS
#include <nfs/nfs.h>
exportfs(
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:
union exportaddrlist {
struct exportfsaddrlist eau_avector;
struct exaddrlist eau_alist;
}
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 */
union exportaddrlist eu_rootaddrs;
/* List of hosts where root can be mapped
* to uid 0 */
union exportaddrlist eu_writeaddrs;
/* List of hosts allowed write access to
* read mostly export */
#define e_rootaddrs eu_rootaddrs.eau_avector
#define e_writeaddrs eu_writeaddrs.eau_avector
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 conjunction 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 database, e_more will be zero
after the system call completes.
To specify and retrieve more than EXMAXADDRS hosts in the root or write
address lists, use the EXPORTFS_LISTPTR access modifier. This is or'd in
with either the EXPORTFS_CREATE or EXPORTFS_READ access flag. When
creating an export, the host list is read from the address pointed to by
eau_alist.addrvec. Similarly, when reading an export, the host list is
written to an already allocated array pointed to by eau_alist.addrvec; the
number of elements allocated is indicated by eau_alist.naddrs. If there
are more hosts to read than are allocated, the allocated array is filled
with as many addresses as will fit, but the returned count will reflect the
actual number available. You can then extend the allocated array to the
returned number of addresses, and retry the read.
The exportfs system call returns a value of 0 upon successful completion of
an operation, and -1 upon failure.
ERRORS
[EPERM]
Not superuser.
[EIO]
Not enough memory in the system to service the request.
[EFAULT]
Bad address for exdata or cookie.
[ENOENT]
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.
[EREMOTE]
Access is EXPORTFS_CREATE and e_path is an NFS mounted directory. Only
local directories can be exported.
[EINVAL]
The exdata pointer is NULL, the cookie value is negative, or the access
flag is invalid.
SEE ALSO
Files: exports(4)
Daemons: mountd(8)
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