Extended Attributes

EA System Calls

Basic system calls:

setxattr()
getxattr()
removexattr()
listxattr()

Each of the above accepts a pathname argument.

There are alternate forms for working on symbolic links or open file descriptors, e.g., lsetxattr(), fsetxattr() (cf. stat(), lstat(), fstat()).

int setxattr(const char *pathname, const char *name,
const void *value, size_t size, int flags)

Set an EA for pathname, using name and value.

name is a null-terminated string.

size is length of value.

By default (i.e., flags == 0), setfxattr() creates new name or overwrites existing name as required.

flags can be:
0;
XATTR_CREATE, give an error if name is already defined; or
XATTR_REPLACE, give an error if name is not already defined.

Example:
    char *value;

    value = "The past is not dead.";
    setxattr(pathname, "user.x", value, strlen(value), 0);

ssize_t getxattr(const char *pathname, const char *name,
void *value, size_t size)

Retrieves current value of name for pathname, and places it in value.

size specifies space available in value.

Returns number of bytes copied into value.

int removexattr(const char *pathname, const char *name)

Remove EA name from pathname.

ssize_t listxattr(const char *pathname, char *list, size_t size)

Returns a list containing names of all EAs associated with pathname.

List is returned as a series of null-separated strings in list.

size specifies space available in list.

Returns the number of bytes copied into list.

Call fails if size is too small; making a call with size == 0 can be used to obtain size required for list.

Obtain corresponding values by calling getxattr() for each name in list.