EXTATTR_GET_FILE(2) | System Calls Manual | 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

`#include <sys/types.h>`
`#include <sys/extattr.h>`

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. Each list entry consists of a single byte containing the length of the attribute name, followed by the attribute name. The attribute name is not terminated by ASCII 0 (nul). 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.

The `extattr_delete_file`() function returns the value 0 if successful; otherwise 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:

[`EACCES`]
  Search permission is denied for a component of the path prefix.
[`ENAMETOOLONG`]
  A component of a pathname exceeded {`NAME_MAX`} characters, or an entire path name exceeded {`PATH_MAX`} characters.
[`ENOENT`]
  A component of the path name that must exist does not exist.
[`ENOTDIR`]
  A component of the path prefix is not a directory.

# SEE ALSO

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

# HISTORY

Extended attribute support was developed as part of the TrustedBSD Project, and introduced in FreeBSD 5.0 and NetBSD 3.0. 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.

Note that previous versions of this man page incorrectly stated that `extattr_list_file`() returned a list of attribute names separated by ASCII 0 (nul).

August 3, 2011 | NetBSD 9.2