EXTATTR(2) BSD System Calls Manual EXTATTR(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 represent‐
ing 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() sys‐
tem 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() and extattr_list_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 sym‐
links.
The extattr_get_fd(), extattr_set_fd(), extattr_delete_fd(), and
extattr_list_fd(), calls are identical to their "_file" counterparts
except for the first argument. The "_fd" functions take a file descrip‐
tor, 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).
CAVEAT
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.
RETURN VALUES
If successful, the extattr_get_file(), extattr_set_file(), and
extattr_list_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() and extattr_list_file() return 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 mem‐
ory 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(), extattr_delete_fd(), and
extattr_list_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:
[ENOATTR] The requested attribute was not defined for this file.
[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 ALSOextattr(3), getextattr(8), setextattr(8), extattr(9), VOP_GETEXTATTR(9),
VOP_SETEXTATTR(9)HISTORY
Extended attribute support was developed as part of the TrustedBSD
Project, and introduced in FreeBSD 5.0. It was developed to support
security extensions requiring additional labels to be associated with
each file or directory.
BUGS
In earlier versions of this API, passing an empty string for the
attribute name to extattr_get_fd(), extattr_get_file(), or
extattr_get_link() would return the list of attributes defined for the
target object. This interface has been deprecated in preference to using
the explicit list API, and should not be used.
BSD January 29, 2008 BSD
