iget: remove iget() and the read_inode() super op as being obsolete

prototypes:

	struct inode *(*alloc_inode)(struct super_block *sb);

	void (*destroy_inode)(struct inode *);

	void (*read_inode) (struct inode *);

	void (*dirty_inode) (struct inode *);

	int (*write_inode) (struct inode *, int);

	void (*put_inode) (struct inode *);

			BKL	s_lock	s_umount

alloc_inode:		no	no	no

destroy_inode:		no

read_inode:		no				(see below)

dirty_inode:		no				(must not sleep)

write_inode:		no

put_inode:		no

quota_read:		no	no	no		(see below)

quota_write:		no	no	no		(see below)

->read_inode() is not a method - it's a callback used in iget().

->remount_fs() will have the s_umount lock if it's already mounted.

When called from get_sb_single, it does NOT have the s_umount lock.

->quota_read() and ->quota_write() functions are both guaranteed to

Make them ->alloc_inode and ->destroy_inode in your super_operations.

Keep in mind that now you need explicit initialization of private data -

typically in ->read_inode() and after getting an inode from new_inode().

Keep in mind that now you need explicit initialization of private data

typically between calling iget_locked() and unlocking the inode.

At some point that will become mandatory.

newly created inode to allow the test function to succeed. 'data' is

passed as an opaque value to both test and set functions.

When the inode has been created by iget5_locked(), it will be returned with

the I_NEW flag set and will still be locked. read_inode has not been

called so the file system still has to finalize the initialization. Once

the inode is initialized it must be unlocked by calling unlock_new_inode().

When the inode has been created by iget5_locked(), it will be returned with the

I_NEW flag set and will still be locked.  The filesystem then needs to finalize

the initialization. Once the inode is initialized it must be unlocked by

calling unlock_new_inode().

The filesystem is responsible for setting (and possibly testing) i_ino

when appropriate. There is also a simpler iget_locked function that

        struct inode *(*alloc_inode)(struct super_block *sb);

        void (*destroy_inode)(struct inode *);

        void (*read_inode) (struct inode *);

        void (*dirty_inode) (struct inode *);

        int (*write_inode) (struct inode *, int);

        void (*put_inode) (struct inode *);

  	->alloc_inode was defined and simply undoes anything done by

	->alloc_inode.

  read_inode: this method is called to read a specific inode from the

        mounted filesystem.  The i_ino member in the struct inode is

	initialized by the VFS to indicate which inode to read. Other

	members are filled in by this method.

	You can set this to NULL and use iget5_locked() instead of iget()

	to read inodes.  This is necessary for filesystems for which the

	inode number is not sufficient to identify an inode.

  dirty_inode: this method is called by the VFS to mark an inode dirty.

  write_inode: this method is called when the VFS needs to write an

  quota_write: called by the VFS to write to filesystem quota file.

The read_inode() method is responsible for filling in the "i_op"

field. This is a pointer to a "struct inode_operations" which

describes the methods that can be performed on individual inodes.

Whoever sets up the inode is responsible for filling in the "i_op" field. This

is a pointer to a "struct inode_operations" which describes the methods that

can be performed on individual inodes.

The Inode Object

 * @set:	callback used to initialize a new struct inode

 * @data:	opaque data pointer to pass to @test and @set

 *

 * This is iget() without the read_inode() portion of get_new_inode().

 *

 * iget5_locked() uses ifind() to search for the inode specified by @hashval

 * and @data in the inode cache and if present it is returned with an increased

 * reference count. This is a generalized version of iget_locked() for file

 * @sb:		super block of file system

 * @ino:	inode number to get

 *

 * This is iget() without the read_inode() portion of get_new_inode_fast().

 *

 * iget_locked() uses ifind_fast() to search for the inode specified by @ino in

 * the inode cache and if present it is returned with an increased reference

 * count. This is for file systems where the inode number is sufficient for

   	struct inode *(*alloc_inode)(struct super_block *sb);

	void (*destroy_inode)(struct inode *);

	void (*read_inode) (struct inode *);

   	void (*dirty_inode) (struct inode *);

	int (*write_inode) (struct inode *, int);

	void (*put_inode) (struct inode *);

extern struct inode * iget_locked(struct super_block *, unsigned long);

extern void unlock_new_inode(struct inode *);

static inline struct inode *iget(struct super_block *sb, unsigned long ino)

{

	struct inode *inode = iget_locked(sb, ino);

	if (inode && (inode->i_state & I_NEW)) {

		sb->s_op->read_inode(inode);

		unlock_new_inode(inode);

	}

	return inode;

}

extern void __iget(struct inode * inode);

extern void iget_failed(struct inode *);

extern void clear_inode(struct inode *);