xfs: add a helper to figure out the space log reservation per item

#include "xfs_extent_busy.h"

#include "xfs_bmap.h"

#include "xfs_quota.h"

#include "xfs_qm.h"

#include "xfs_trans_priv.h"

#include "xfs_trans_space.h"

#include "xfs_inode_item.h"

#include "xfs_log_priv.h"

#include "xfs_buf_item.h"

#include "xfs_trace.h"

kmem_zone_t	*xfs_trans_zone;

kmem_zone_t	*xfs_log_item_desc_zone;

/*

 * A buffer has a format structure overhead in the log in addition

 * to the data, so we need to take this into account when reserving

 * space in a transaction for a buffer.  Round the space required up

 * to a multiple of 128 bytes so that we don't change the historical

 * reservation that has been used for this overhead.

 */

STATIC uint

xfs_buf_log_overhead(void)

{

	return round_up(sizeof(struct xlog_op_header) +

			sizeof(struct xfs_buf_log_format), 128);

}

/*

 * Calculate out transaction log reservation per item in bytes.

 *

 * The nbufs argument is used to indicate the number of items that

 * will be changed in a transaction.  size is used to tell how many

 * bytes should be reserved per item.

 */

STATIC uint

xfs_calc_buf_res(

	uint		nbufs,

	uint		size)

{

	return nbufs * (size + xfs_buf_log_overhead());

}

/*

 * Various log reservation values.