struct export_operat(9)

NAME

struct export_operations - for nfsd to communicate with

file systems

SYNOPSIS

struct export_operations {
  struct dentry *(* decode_fh) (struct super_block *sb,
__u32 *fh, int fh_len, int fh_type,int (*acceptable);
  int (* encode_fh) (struct dentry *de, __u32 *fh,  int
*max_len,int connectable);
  int   (*   get_name)  (struct  dentry  *parent,  char
*name,struct dentry *child);
  struct  dentry  *  (*  get_parent)   (struct   dentry
*child);
  struct  dentry  *  (* get_dentry) (struct super_block
*sb, void *inump);
  struct dentry * (* find_exported_dentry) (struct  super_block *sb, void *obj, void *parent,int (*acceptable);
};

MEMBERS

decode_fh

decode a file handle fragment and return a &struct den

try

encode_fh

encode a file handle fragment from a dentry

get_name

find the name for a given inode in a given directory

get_parent

find the parent of a given directory

get_dentry

find a dentry for the inode given a file handle sub

fragment

find_exported_dentry

set by the exporting module to a standard helper func

tion.

DESCRIPTION

The export_operations structure provides a means for nfsd

to communicate with a particular exported file system - particu

larly enabling nfsd and the filesystem to co-operate when dealing

with file handles.

export_operations contains two basic operation for dealing

with file handles, decode_fh and encode_fh, and allows for some

other operations to be defined which standard helper routines use

to get specific information from the filesystem.

nfsd encodes information use to determine which filesystem

a filehandle applies to in the initial part of the file handle.

The remainder, termed a file handle fragment, is controlled com

pletely by the filesystem. The standard helper routines assume

that this fragment will contain one or two sub-fragments, one

which identifies the file, and one which may be used to identify

the (a) directory containing the file.

In some situations, nfsd needs to get a dentry which is

connected into a specific part of the file tree. To allow for

this, it passes the function acceptable together with a context

which can be used to see if the dentry is acceptable. As there

can be multiple dentrys for a given file, the filesystem should

check each one for acceptability before looking for the next. As

soon as an acceptable one is found, it should be returned.

DECODE_FH

decode_fh is given a &struct super_block (sb), a file han

dle fragment (fh, fh_len) and an acceptability testing function

(acceptable, context). It should return a &struct dentry which

refers to the same file that the file handle fragment refers to,

and which passes the acceptability test. If it cannot, it should

return a NULL pointer if the file was found but no acceptable

&dentries were available, or a ERR_PTR error code indicating why

it couldn't be found (e.g. ENOENT or ENOMEM).

ENCODE_FH

encode_fh should store in the file handle fragment fh (us

ing at most max_len bytes) information that can be used by

decode_fh to recover the file refered to by the &struct dentry

de. If the connectable flag is set, the encode_fh should store

sufficient information so that a good attempt can be made to find

not only the file but also it's place in the filesystem. This

typically means storing a reference to de->d_parent in the file

handle fragment. encode_fh should return the number of bytes

stored or a negative error code such as -ENOSPC

GET_NAME

get_name should find a name for the given child in the

given parent directory. The name should be stored in the name

(with the understanding that it is already pointing to a a

NAME_MAX

negative error code or error. get_name will be called without parent->i_mutex held.

GET_PARENT

get_parent should find the parent directory for the given

child which is also a directory. In the event that it cannot be

found, or storage space cannot be allocated, a ERR_PTR should be

returned.

GET_DENTRY

Given a &super_block (sb) and a pointer to a file-system

specific inode identifier, possibly an inode number, (inump)

get_dentry should find the identified inode and return a dentry

for that inode. Any suitable dentry can be returned including, if

necessary, a new dentry created with d_alloc_root. The caller can

then find any other extant dentrys by following the d_alias

links. If a new dentry was created using d_alloc_root,

DCACHE_NFSD_DISCONNECTED should be set, and the dentry should be

d_rehashed.

If the inode cannot be found, either a NULL pointer or an

ERR_PTR

passed to nfsd_find_fh_dentry in either the obj or parent parameters.

LOCKING RULES

get_parent is called with child->d_inode->i_mutex down

get_name is not (which is possibly inconsistent)

COPYRIGHT

STRUCT EXPORT_OPERAT(9)