Implementation of Buffer Headers in Linux kernel

[Dinesh Ahuja]

I have a few queries regarding the buffer headers in
linux. I a newbie so these queries may sound stupid to
linux gurus.

1. As per my understanding, block number in this
stucture corresponds to the block no of the data on a
logical device rather than on a physical device (hard
disk).

2. Why do we need pointer to a pointer for hash list ?
As per Maurice Bach book on OS, the hash list and free
list both are implemented as a circular, doubly link
list.

In the below, we have used a pointer for free list,
then why pointer to pointer has been used for hash
list.

struct buffer_head {
	/* First cache line: */
	struct buffer_head *b_next;	/* Hash queue list */
	struct buffer_head *b_next_free;/* lru/free list
linkage */
	struct buffer_head *b_prev_free;/* doubly linked list
of buffers */
	struct buffer_head **b_pprev;	/* doubly linked list
of hash-queue */
        // Rest part of sructure has been stripped
off.    
};


Can anyone clarify my these queries.

Thanks & Regards
Dinesh

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