hfsplus: reworked support of extended attributes.

Current mainline implementation of hfsplus file system driver treats as
extended attributes only two fields (fdType and fdCreator) of user_info
field in file description record (struct hfsplus_cat_file).  It is
possible to get or set only these two fields as extended attributes.
But HFS+ treats as com.apple.FinderInfo extended attribute an union of
user_info and finder_info fields as for file (struct hfsplus_cat_file)
as for folder (struct hfsplus_cat_folder).  Moreover, current mainline
implementation of hfsplus file system driver doesn't support special
metadata file - attributes tree.

Mac OS X 10.4 and later support extended attributes by making use of the
HFS+ filesystem Attributes file B*-tree feature which allows for named
forks.  Mac OS X supports only inline extended attributes, limiting
their size to 3802 bytes.  Any regular file may have a list of extended
attributes.  HFS+ supports an arbitrary number of named forks.  Each
attribute is denoted by a name and the associated data.  The name is a
null-terminated Unicode string.  It is possible to list, to get, to set,
and to remove extended attributes from files or directories.

It exists some peculiarity during getting of extended attributes list by
means of getfattr utility.  The getfattr utility expects prefix "user."
before any extended attribute's name.  So, it ignores any names that
don't contained such prefix.  Such behavior of getfattr utility results
in unexpected empty output of extended attributes list even in the case
when file (or folder) contains extended attributes.  It needs to use
empty string as regular expression pattern for names matching (getfattr
--match="").

For support of extended attributes in HFS+:
1. It was added necessary on-disk layout declarations related to Attributes
   tree into hfsplus_raw.h file.
2. It was added attributes.c file with implementation of functionality of
   manipulation by records in Attributes tree.
3. It was reworked hfsplus_listxattr, hfsplus_getxattr, hfsplus_setxattr
   functions in ioctl.c. Moreover, it was added hfsplus_removexattr method.

This patch:

Add osx.* prefix for handling namespace of Mac OS X extended attributes.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: NVyacheslav Dubeyko <slava@dubeyko.com>
Reported-by: NHin-Tak Leung <htl10@users.sourceforge.net>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>