[PATCH] XATTR support in JFFS2

[Ma Yun]

Thank joern! I am sorry for my poor kernel code experience.

I have modified the patch.

Below is the implemention mechanism :)

1. background

The implementing of EAs in jffs2 is based on Epxa embedded board.

(ARM920T core+ 64M SDRAM + 16M NOR FLASH ...)

In our project, the extended attributes name length and value length are no 
more
than 256 bytes. So I defined the EA structure like this:
      struct jffs2_xattr {
	uint8_t namelen;	/* Length of name */
	uint8_t valuelen;	/* Length of value */
	char name[0];             /* Attribute name (include null-terminator)*/
		                 /* Attribute Valude immediately follows name*/
      }__attribute__((packed));

2. Overall design

. Extended attributes are stored in-lined in the dirent inode.
. The extended attributes list consist of a veriable (0 or more) number of
   extended attribute entries.
. Each extended attribute entry is a <name, value> pair where <name>
   is constructed from a null-terminated ascii string and <value> is 
arbitrary
   data.
. The EA name/value are not loaded until we get/set/list/remove them. Read 
them
   from flash directly.

Extended attribute entry format:

0                  1                   2                       2 + namelen + 
1
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
|Name length | Value length | Name string  \0| Value ...	 |
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Extended attribute list format:

0                        JFFS2_XATTR_SIZE(ea1)
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| First EA element | Second EA element | ......                 |
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Extended attribute list store in-lined in the dirent inode.

Just like below:
+++++++++++++++++++++++++++++++++++++++++++++++++++
| Common head   |pino |   ......   |node_crc|name_crc|name... |EA list...|
+++++++++++++++++++++++++++++++++++++++++++++++++++

3. Data structure

- jffs2_xattr

struct jffs2_xattr {
	uint8_t namelen;
	uint8_t valuelen;
	char name[0];

}__attribute__((packed));

- jffs2_xattr_list

struct jffs2_xattr_list {
	struct jffs2_xattr xattr[0];
}__attribute__((packed));

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