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OSX 10.6.2 - man page for getxattr (osx section 2)

GETXATTR(2)						      BSD System Calls Manual						       GETXATTR(2)

getxattr, fgetxattr -- get an extended attribute value
#include <sys/xattr.h> ssize_t getxattr(const char *path, const char *name, void *value, size_t size, u_int32_t position, int options); ssize_t fgetxattr(int fd, const char *name, void *value, size_t size, u_int32_t position, int options);
Extended attributes extend the basic attributes of files and directories in the file system. They are stored as name:data pairs associated with file system objects (files, directories, symlinks, etc). The getxattr() function retrieves up to size bytes of data from the extended attribute identified by name associated with path into the pre- allocated buffer pointed to by value. The function returns the number of bytes of data retrieved. An extended attribute's name is a simple NULL-terminated UTF-8 string. position specifies an offset within the extended attribute. In the current implementation, this argument is only used with the resource fork attribute. For all other extended attributes, this parameter is reserved and should be zero. On success, value contains the data associated with name. When value is set to NULL, getxattr() returns current size of the named attribute. This facility can be used to determine the size of a buffer sufficiently large to hold the data currently associated with the attribute. options specify options for retrieving extended attributes: XATTR_NOFOLLOW do not follow symbolic links. getxattr() normally returns information from the target of path if it is a symbolic link. With this option, getxattr() will return extended attribute data from the symbolic link instead. XATTR_SHOWCOMPRESSION getxattr() and fgetxattr() will return HFS Plus Compression extended attribute name (if present) for the file referred to by path or fd. fgetxattr() is identical to getxattr(), except that it retrieves extended attribute data from the open file referenced by the file descriptor fd.
On success, the size of the extended attribute data is returned. On failure, -1 is returned and the global variable errno is set as follows.
[ENOATTR] The extended attribute does not exist. [ENOTSUP] The file system does not support extended attributes or has the feature disabled. [ERANGE] value (as indicated by size) is too small to hold the extended attribute data. [EPERM] The named attribute is not permitted for this type of object. [EINVAL] name is invalid or options has an unsupported bit set. [EISDIR] path or fd do not refer to a regular file and the attribute in question is only applicable to files. Similar to EPERM. [ENOTDIR] A component of path 's prefix is not a directory. [ENAMETOOLONG] The length of name exceeds XATTR_MAXNAMELEN UTF-8 bytes, or a component of path exceeds NAME_MAX characters, or the entire path exceeds PATH_MAX characters. [EACCES] Search permission is denied for a component of path or the attribute is not allowed to be read (e.g. an ACL prohibits reading the attributes of this file). [ELOOP] Too many symbolic links were encountered in translating the pathname. [EFAULT] path or name points to an invalid address. [EIO] An I/O error occurred while reading from or writing to the file system.
listxattr(2), removexattr(2), setxattr(2)
getxattr() and fgetxattr() first appeared in Mac OS X 10.4. Mac OS X Oct 19, 2004 Mac OS X