exportfs - Export an NFS file system
#include <nfs/nfs.h>
exportfs(
int access,
int *cookie,
struct exportfsdata *exdata );
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.
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.
Files: exports(4)
Daemons: mountd(8)
exportfs(2)
[ Back ] |
