---
name: "struct_export_operations"
section: "9"
platform: "linux"
package: "linux-manual-2.6.18"
version: "2.6.18.dfsg.1-26etch2"
release: "Debian 4.0 (Etch)"
platforms: ["linux"]
url: "https://new.carta.tech/struct_export_operations"
---

# struct\_export\_operations(9)

for nfsd to communicate with file systems

## 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 dentry

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 function.

## DESCRIPTION

The export\_operations structure provides a means for nfsd to communicate with a particular exported file system - particularly 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 completely 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 handle 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* (using 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 filehandle 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**+1 sized buffer. **get\_name** should return **0** on success, a 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\_rehash**ed.

If the inode cannot be found, either a **NULL** pointer or an **ERR\_PTR** code can be returned. The *inump* will be whatever was 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