January 2, 2004 EXTATTR_GET_FILE 2

### NAME

extattr_get_fd, extattr_set_fd, extattr_delete_fd, extattr_list_fd, extattr_get_file, extattr_set_file, extattr_delete_file, extattr_list_file, extattr_get_link, extattr_set_link, extattr_delete_link, extattr_list_link - system calls to manipulate VFS extended attributes

### LIBRARY

Standard C Library (libc, -lc)

### SYNOPSIS

```ssize_t` extattr_get_fd(```int fd``, int attrnamespace``, const char *attrname``, void *data``, size_t nbytes`)
```int` extattr_set_fd(```int fd``, int attrnamespace``, const char *attrname``, const void *data``, size_t nbytes`)
```int` extattr_delete_fd(```int fd``, int attrnamespace``, const char *attrname`)
```ssize_t` extattr_list_fd(```int fd``, int attrnamespace``, void *data``, size_t nbytes`)
```ssize_t` extattr_get_file(```const char *path``, int attrnamespace``, const char *attrname``, void *data``, size_t nbytes`)
```int` extattr_set_file(```const char *path``, int attrnamespace``, const char *attrname``, const void *data``, size_t nbytes`)
```int` extattr_delete_file(```const char *path``, int attrnamespace``, const char *attrname`)
```ssize_t` extattr_list_file(```const char *path``, int attrnamespace``, void *data``, size_t nbytes`)
```ssize_t` extattr_get_link(```const char *path``, int attrnamespace``, const char *attrname``, void *data``, size_t nbytes`)
```int` extattr_set_link(```const char *path``, int attrnamespace``, const char *attrname``, const void *data``, size_t nbytes`)
```int` extattr_delete_link(```const char *path``, int attrnamespace``, const char *attrname`)
```ssize_t` extattr_list_link(```const char *path``, int attrnamespace``, void *data``, size_t nbytes`)

### DESCRIPTION

Named extended attributes are meta-data associated with vnodes representing files and directories. They exist as "```name=value` pairs within a set of namespaces.

The extattr_get_file(``) system call retrieves the value of the specified extended attribute into a buffer pointed to by ```data` of size ```nbytes`. The extattr_set_file(``) system call sets the value of the specified extended attribute to the data described by ```data`. The extattr_delete_file(``) system call deletes the extended attribute specified. The extattr_list_file(``) returns a list of attributes present in the requested namespace, separated by ASCII 0 (nul) characters. The extattr_get_file(``) and extattr_list_file(``) calls consume the ```data` and ```nbytes` arguments in the style of read(2); extattr_set_file(``) consumes these arguments in the style of write(2).

If ```data` is ```NULL` in a call to extattr_get_file(``) then the size of defined extended attribute data will be returned, rather than the quantity read, permitting applications to test the size of the data without performing a read.

The extattr_delete_link(``), extattr_get_link(``), and extattr_set_link(``) system calls behave in the same way as their _file counterparts, except that they do not follow symlinks.

The extattr_get_fd(``), extattr_set_fd(``), and extattr_delete_fd(``) calls are identical to their "```_file` counterparts except for the first argument. The "```_fd` functions take a file descriptor, while the "```_file` functions take a path. Both arguments describe a file associated with the extended attribute that should be manipulated.

The following arguments are common to all the system calls described here:

```attrnamespace`
  the namespace in which the extended attribute resides; see extattr(9)

```attrname`
  the name of the extended attribute

Named extended attribute semantics vary by file system implementing the call. Not all operations may be supported for a particular attribute. Additionally, the format of the data in ```data` is attribute-specific.

For more information on named extended attributes, please see extattr(9).

### RETURN VALUES

If successful, the extattr_get_file(``) and extattr_set_file(``) calls return the number of bytes that were read or written from the ```data`, respectively, or if ```data` was ```NULL`, then extattr_get_file(``) returns the number of bytes available to read. If any of the calls are unsuccessful, the value -1 is returned and the global variable errno is set to indicate the error.

### ERRORS

The following errors may be returned by the system calls themselves. Additionally, the file system implementing the call may return any other errors it desires.

[```EFAULT`]
  The ```attrnamespace` and ```attrname` arguments, or the memory range defined by ```data` and ```nbytes` point outside the process's allocated address space.

[```ENAMETOOLONG`]
  The attribute name was longer than ```EXTATTR_MAXNAMELEN`.

The extattr_get_fd(``), extattr_set_fd(``), and extattr_delete_fd(``) system calls may also fail if:

[```EBADF`]
  The file descriptor referenced by ```fd` was invalid.

Additionally, the extattr_get_file(``), extattr_set_file(``), and extattr_delete_file(``) calls may also fail due to the following errors:

[```ENOTDIR`]
  A component of the path prefix is not a directory.

[```ENAMETOOLONG`]
  A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.

[```ENOENT`]
  A component of the path name that must exist does not exist.

[```EACCES`]
  Search permission is denied for a component of the path prefix.

### SEE ALSO

getextattr(1), extattr(3), extattr(9)

### HISTORY

Extended attribute support was developed as part of the TrustedBSD Project, and introduced in FreeBSD5.0 and NetBSD3.0. It was developed to support security extensions requiring additional labels to be associated with each file or directory.

### CAVEATS

This interface is under active development, and as such is subject to change as applications are adapted to use it. Developers are discouraged from relying on its stability.