LIBRARY

Lb libc

SYNOPSIS

In sys/types.h In sys/extattr.h Ft ssize_t Fn extattr_get_fd int fd int attrnamespace const char *attrname void *data size_t nbytes Ft ssize_t Fn extattr_set_fd int fd int attrnamespace const char *attrname const void *data size_t nbytes Ft int Fn extattr_delete_fd int fd int attrnamespace const char *attrname Ft ssize_t Fn extattr_list_fd int fd int attrnamespace void *data size_t nbytes Ft ssize_t Fn extattr_get_file const char *path int attrnamespace const char *attrname void *data size_t nbytes Ft ssize_t Fn extattr_set_file const char *path int attrnamespace const char *attrname const void *data size_t nbytes Ft int Fn extattr_delete_file const char *path int attrnamespace const char *attrname Ft ssize_t Fn extattr_list_file const char *path int attrnamespace void *data size_t nbytes Ft ssize_t Fn extattr_get_link const char *path int attrnamespace const char *attrname void *data size_t nbytes Ft ssize_t Fn extattr_set_link const char *path int attrnamespace const char *attrname const void *data size_t nbytes Ft int Fn extattr_delete_link const char *path int attrnamespace const char *attrname Ft ssize_t Fn 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 Qq Li name=value pairs within a set of namespaces.

The Fn extattr_get_file system call retrieves the value of the specified extended attribute into a buffer pointed to by Fa data of size Fa nbytes . The Fn extattr_set_file system call sets the value of the specified extended attribute to the data described by Fa data . The Fn extattr_delete_file system call deletes the extended attribute specified. The Fn 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 Fn extattr_get_file , and Fn extattr_list_file calls consume the Fa data and Fa nbytes arguments in the style of read(2); Fn extattr_set_file consumes these arguments in the style of write(2).

If Fa data is NULL in a call to Fn extattr_get_file and Fn 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 Fn extattr_delete_link , Fn extattr_get_link , and Fn extattr_set_link system calls behave in the same way as their _file counterparts, except that they do not follow symlinks.

The Fn extattr_get_fd , Fn extattr_set_fd , Fn extattr_delete_fd , and Fn extattr_list_fd , calls are identical to their Qq Li _file counterparts except for the first argument. The Qq Li _fd functions take a file descriptor, while the Qq Li _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:

Fa attrnamespace

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

Fa 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 Fa 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 Fn extattr_get_file , Fn extattr_set_file , and Fn extattr_list_file calls return the number of bytes that were read or written from the Fa data , respectively, or if Fa data was NULL then Fn extattr_get_file and Fn 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.

Rv -std extattr_delete_file

HISTORY

Extended attribute support was developed as part of the TrustedBSD Project, and introduced in Fx 5.0 . It was developed to support security extensions requiring additional labels to be associated with each file or directory.