drivers/infiniband/ulp/iser/iser_memory.c - maze/linux - Git at Google

 /*
  * Copyright (c) 2004, 2005, 2006 Voltaire, Inc. All rights reserved.
  *
  * This software is available to you under a choice of one of two
  * licenses.  You may choose to be licensed under the terms of the GNU
  * General Public License (GPL) Version 2, available from the file
  * COPYING in the main directory of this source tree, or the
  * OpenIB.org BSD license below:
  *
  *     Redistribution and use in source and binary forms, with or
  *     without modification, are permitted provided that the following
  *     conditions are met:
  *
  *	- Redistributions of source code must retain the above
  *	  copyright notice, this list of conditions and the following
  *	  disclaimer.
  *
  *	- Redistributions in binary form must reproduce the above
  *	  copyright notice, this list of conditions and the following
  *	  disclaimer in the documentation and/or other materials
  *	  provided with the distribution.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  *
  * $Id: iser_memory.c 6964 2006-05-07 11:11:43Z ogerlitz $
  */
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
 #include <asm/io.h>
 #include <asm/scatterlist.h>
 #include <linux/scatterlist.h>

 #include "iscsi_iser.h"

 #define ISER_KMALLOC_THRESHOLD 0x20000 /* 128K - kmalloc limit */
 /**
  * Decrements the reference count for the
  * registered buffer & releases it
  *
  * returns 0 if released, 1 if deferred
  */
 int iser_regd_buff_release(struct iser_regd_buf *regd_buf)
 {
 	struct device *dma_device;

 	if ((atomic_read(&regd_buf->ref_count) == 0) ||
 	    atomic_dec_and_test(&regd_buf->ref_count)) {
 		/* if we used the dma mr, unreg is just NOP */
 		if (regd_buf->reg.rkey != 0)
 			iser_unreg_mem(&regd_buf->reg);

 		if (regd_buf->dma_addr) {
 			dma_device = regd_buf->device->ib_device->dma_device;
 			dma_unmap_single(dma_device,
 					 regd_buf->dma_addr,
 					 regd_buf->data_size,
 					 regd_buf->direction);
 		}
 		/* else this regd buf is associated with task which we */
 		/* dma_unmap_single/sg later */
 		return 0;
 	} else {
 		iser_dbg("Release deferred, regd.buff: 0x%p\n", regd_buf);
 		return 1;
 	}
 }

 /**
  * iser_reg_single - fills registered buffer descriptor with
  *		     registration information
  */
 void iser_reg_single(struct iser_device *device,
 		     struct iser_regd_buf *regd_buf,
 		     enum dma_data_direction direction)
 {
 	dma_addr_t dma_addr;

 	dma_addr  = dma_map_single(device->ib_device->dma_device,
 				   regd_buf->virt_addr,
 				   regd_buf->data_size, direction);
 	BUG_ON(dma_mapping_error(dma_addr));

 	regd_buf->reg.lkey = device->mr->lkey;
 	regd_buf->reg.rkey = 0; /* indicate there's no need to unreg */
 	regd_buf->reg.len  = regd_buf->data_size;
 	regd_buf->reg.va   = dma_addr;

 	regd_buf->dma_addr  = dma_addr;
 	regd_buf->direction = direction;
 }

 /**
  * iser_start_rdma_unaligned_sg
  */
 int iser_start_rdma_unaligned_sg(struct iscsi_iser_cmd_task  *iser_ctask,
 				 enum iser_data_dir cmd_dir)
 {
 	int dma_nents;
 	struct device *dma_device;
 	char *mem = NULL;
 	struct iser_data_buf *data = &iser_ctask->data[cmd_dir];
 	unsigned long  cmd_data_len = data->data_len;

 	if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
 		mem = (void *)__get_free_pages(GFP_NOIO,
 		      long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
 	else
 		mem = kmalloc(cmd_data_len, GFP_NOIO);

 	if (mem == NULL) {
 		iser_err("Failed to allocate mem size %d %d for copying sglist\n",
 			 data->size,(int)cmd_data_len);
 		return -ENOMEM;
 	}

 	if (cmd_dir == ISER_DIR_OUT) {
 		/* copy the unaligned sg the buffer which is used for RDMA */
 		struct scatterlist *sg = (struct scatterlist *)data->buf;
 		int i;
 		char *p, *from;

 		for (p = mem, i = 0; i < data->size; i++) {
 			from = kmap_atomic(sg[i].page, KM_USER0);
 			memcpy(p,
 			       from + sg[i].offset,
 			       sg[i].length);
 			kunmap_atomic(from, KM_USER0);
 			p += sg[i].length;
 		}
 	}

 	sg_init_one(&iser_ctask->data_copy[cmd_dir].sg_single, mem, cmd_data_len);
 	iser_ctask->data_copy[cmd_dir].buf  =
 		&iser_ctask->data_copy[cmd_dir].sg_single;
 	iser_ctask->data_copy[cmd_dir].size = 1;

 	iser_ctask->data_copy[cmd_dir].copy_buf  = mem;

 	dma_device = iser_ctask->iser_conn->ib_conn->device->ib_device->dma_device;

 	if (cmd_dir == ISER_DIR_OUT)
 		dma_nents = dma_map_sg(dma_device,
 				       &iser_ctask->data_copy[cmd_dir].sg_single,
 				       1, DMA_TO_DEVICE);
 	else
 		dma_nents = dma_map_sg(dma_device,
 				       &iser_ctask->data_copy[cmd_dir].sg_single,
 				       1, DMA_FROM_DEVICE);

 	BUG_ON(dma_nents == 0);

 	iser_ctask->data_copy[cmd_dir].dma_nents = dma_nents;
 	return 0;
 }

 /**
  * iser_finalize_rdma_unaligned_sg
  */
 void iser_finalize_rdma_unaligned_sg(struct iscsi_iser_cmd_task *iser_ctask,
 				     enum iser_data_dir         cmd_dir)
 {
 	struct device *dma_device;
 	struct iser_data_buf *mem_copy;
 	unsigned long  cmd_data_len;

 	dma_device = iser_ctask->iser_conn->ib_conn->device->ib_device->dma_device;
 	mem_copy   = &iser_ctask->data_copy[cmd_dir];

 	if (cmd_dir == ISER_DIR_OUT)
 		dma_unmap_sg(dma_device, &mem_copy->sg_single, 1,
 			     DMA_TO_DEVICE);
 	else
 		dma_unmap_sg(dma_device, &mem_copy->sg_single, 1,
 			     DMA_FROM_DEVICE);

 	if (cmd_dir == ISER_DIR_IN) {
 		char *mem;
 		struct scatterlist *sg;
 		unsigned char *p, *to;
 		unsigned int sg_size;
 		int i;

 		/* copy back read RDMA to unaligned sg */
 		mem	= mem_copy->copy_buf;

 		sg	= (struct scatterlist *)iser_ctask->data[ISER_DIR_IN].buf;
 		sg_size = iser_ctask->data[ISER_DIR_IN].size;

 		for (p = mem, i = 0; i < sg_size; i++){
 			to = kmap_atomic(sg[i].page, KM_SOFTIRQ0);
 			memcpy(to + sg[i].offset,
 			       p,
 			       sg[i].length);
 			kunmap_atomic(to, KM_SOFTIRQ0);
 			p += sg[i].length;
 		}
 	}

 	cmd_data_len = iser_ctask->data[cmd_dir].data_len;

 	if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
 		free_pages((unsigned long)mem_copy->copy_buf,
 			   long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
 	else
 		kfree(mem_copy->copy_buf);

 	mem_copy->copy_buf = NULL;
 }

 /**
  * iser_sg_to_page_vec - Translates scatterlist entries to physical addresses
  * and returns the length of resulting physical address array (may be less than
  * the original due to possible compaction).
  *
  * we build a "page vec" under the assumption that the SG meets the RDMA
  * alignment requirements. Other then the first and last SG elements, all
  * the "internal" elements can be compacted into a list whose elements are
  * dma addresses of physical pages. The code supports also the weird case
  * where --few fragments of the same page-- are present in the SG as
  * consecutive elements. Also, it handles one entry SG.
  */
 static int iser_sg_to_page_vec(struct iser_data_buf *data,
 			       struct iser_page_vec *page_vec)
 {
 	struct scatterlist *sg = (struct scatterlist *)data->buf;
 	dma_addr_t first_addr, last_addr, page;
 	int start_aligned, end_aligned;
 	unsigned int cur_page = 0;
 	unsigned long total_sz = 0;
 	int i;

 	/* compute the offset of first element */
 	page_vec->offset = (u64) sg[0].offset;

 	for (i = 0; i < data->dma_nents; i++) {
 		total_sz += sg_dma_len(&sg[i]);

 		first_addr = sg_dma_address(&sg[i]);
 		last_addr  = first_addr + sg_dma_len(&sg[i]);

 		start_aligned = !(first_addr & ~PAGE_MASK);
 		end_aligned   = !(last_addr  & ~PAGE_MASK);

 		/* continue to collect page fragments till aligned or SG ends */
 		while (!end_aligned && (i + 1 < data->dma_nents)) {
 			i++;
 			total_sz += sg_dma_len(&sg[i]);
 			last_addr = sg_dma_address(&sg[i]) + sg_dma_len(&sg[i]);
 			end_aligned = !(last_addr  & ~PAGE_MASK);
 		}

 		first_addr = first_addr & PAGE_MASK;

 		for (page = first_addr; page < last_addr; page += PAGE_SIZE)
 			page_vec->pages[cur_page++] = page;

 	}
 	page_vec->data_size = total_sz;
 	iser_dbg("page_vec->data_size:%d cur_page %d\n", page_vec->data_size,cur_page);
 	return cur_page;
 }

 #define MASK_4K			((1UL << 12) - 1) /* 0xFFF */
 #define IS_4K_ALIGNED(addr)	((((unsigned long)addr) & MASK_4K) == 0)

 /**
  * iser_data_buf_aligned_len - Tries to determine the maximal correctly aligned
  * for RDMA sub-list of a scatter-gather list of memory buffers, and  returns
  * the number of entries which are aligned correctly. Supports the case where
  * consecutive SG elements are actually fragments of the same physcial page.
  */
 static unsigned int iser_data_buf_aligned_len(struct iser_data_buf *data)
 {
 	struct scatterlist *sg;
 	dma_addr_t end_addr, next_addr;
 	int i, cnt;
 	unsigned int ret_len = 0;

 	sg = (struct scatterlist *)data->buf;

 	for (cnt = 0, i = 0; i < data->dma_nents; i++, cnt++) {
 		/* iser_dbg("Checking sg iobuf [%d]: phys=0x%08lX "
 		   "offset: %ld sz: %ld\n", i,
 		   (unsigned long)page_to_phys(sg[i].page),
 		   (unsigned long)sg[i].offset,
 		   (unsigned long)sg[i].length); */
 		end_addr = sg_dma_address(&sg[i]) +
 			   sg_dma_len(&sg[i]);
 		/* iser_dbg("Checking sg iobuf end address "
 		       "0x%08lX\n", end_addr); */
 		if (i + 1 < data->dma_nents) {
 			next_addr = sg_dma_address(&sg[i+1]);
 			/* are i, i+1 fragments of the same page? */
 			if (end_addr == next_addr)
 				continue;
 			else if (!IS_4K_ALIGNED(end_addr)) {
 				ret_len = cnt + 1;
 				break;
 			}
 		}
 	}
 	if (i == data->dma_nents)
 		ret_len = cnt;	/* loop ended */
 	iser_dbg("Found %d aligned entries out of %d in sg:0x%p\n",
 		 ret_len, data->dma_nents, data);
 	return ret_len;
 }

 static void iser_data_buf_dump(struct iser_data_buf *data)
 {
 	struct scatterlist *sg = (struct scatterlist *)data->buf;
 	int i;

 	for (i = 0; i < data->size; i++)
 		iser_err("sg[%d] dma_addr:0x%lX page:0x%p "
 			 "off:%d sz:%d dma_len:%d\n",
 			 i, (unsigned long)sg_dma_address(&sg[i]),
 			 sg[i].page, sg[i].offset,
 			 sg[i].length,sg_dma_len(&sg[i]));
 }

 static void iser_dump_page_vec(struct iser_page_vec *page_vec)
 {
 	int i;

 	iser_err("page vec length %d data size %d\n",
 		 page_vec->length, page_vec->data_size);
 	for (i = 0; i < page_vec->length; i++)
 		iser_err("%d %lx\n",i,(unsigned long)page_vec->pages[i]);
 }

 static void iser_page_vec_build(struct iser_data_buf *data,
 				struct iser_page_vec *page_vec)
 {
 	int page_vec_len = 0;

 	page_vec->length = 0;
 	page_vec->offset = 0;

 	iser_dbg("Translating sg sz: %d\n", data->dma_nents);
 	page_vec_len = iser_sg_to_page_vec(data,page_vec);
 	iser_dbg("sg len %d page_vec_len %d\n", data->dma_nents,page_vec_len);

 	page_vec->length = page_vec_len;

 	if (page_vec_len * PAGE_SIZE < page_vec->data_size) {
 		iser_err("page_vec too short to hold this SG\n");
 		iser_data_buf_dump(data);
 		iser_dump_page_vec(page_vec);
 		BUG();
 	}
 }

 /**
  * iser_reg_rdma_mem - Registers memory intended for RDMA,
  * obtaining rkey and va
  *
  * returns 0 on success, errno code on failure
  */
 int iser_reg_rdma_mem(struct iscsi_iser_cmd_task *iser_ctask,
 		      enum   iser_data_dir        cmd_dir)
 {
 	struct iser_conn     *ib_conn = iser_ctask->iser_conn->ib_conn;
 	struct iser_data_buf *mem = &iser_ctask->data[cmd_dir];
 	struct iser_regd_buf *regd_buf;
 	int aligned_len;
 	int err;

 	regd_buf = &iser_ctask->rdma_regd[cmd_dir];

 	aligned_len = iser_data_buf_aligned_len(mem);
 	if (aligned_len != mem->size) {
 		iser_err("rdma alignment violation %d/%d aligned\n",
 			 aligned_len, mem->size);
 		iser_data_buf_dump(mem);
 		/* allocate copy buf, if we are writing, copy the */
 		/* unaligned scatterlist, dma map the copy        */
 		if (iser_start_rdma_unaligned_sg(iser_ctask, cmd_dir) != 0)
 				return -ENOMEM;
 		mem = &iser_ctask->data_copy[cmd_dir];
 	}

 	iser_page_vec_build(mem, ib_conn->page_vec);
 	err = iser_reg_page_vec(ib_conn, ib_conn->page_vec, &regd_buf->reg);
 	if (err)
 		return err;

 	/* take a reference on this regd buf such that it will not be released *
 	 * (eg in send dto completion) before we get the scsi response         */
 	atomic_inc(&regd_buf->ref_count);
 	return 0;
 }
	/*
	* Copyright (c) 2004, 2005, 2006 Voltaire, Inc. All rights reserved.
	*
	* This software is available to you under a choice of one of two
	* licenses. You may choose to be licensed under the terms of the GNU
	* General Public License (GPL) Version 2, available from the file
	* COPYING in the main directory of this source tree, or the
	* OpenIB.org BSD license below:
	*
	* Redistribution and use in source and binary forms, with or
	* without modification, are permitted provided that the following
	* conditions are met:
	*
	* - Redistributions of source code must retain the above
	* copyright notice, this list of conditions and the following
	* disclaimer.
	*
	* - Redistributions in binary form must reproduce the above
	* copyright notice, this list of conditions and the following
	* disclaimer in the documentation and/or other materials
	* provided with the distribution.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
	* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
	* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
	* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
	* SOFTWARE.
	*
	* $Id: iser_memory.c 6964 2006-05-07 11:11:43Z ogerlitz $
	*/
	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/slab.h>
	#include <linux/mm.h>
	#include <asm/io.h>
	#include <asm/scatterlist.h>
	#include <linux/scatterlist.h>

	#include "iscsi_iser.h"

	#define ISER_KMALLOC_THRESHOLD 0x20000 /* 128K - kmalloc limit */
	/**
	* Decrements the reference count for the
	* registered buffer & releases it
	*
	* returns 0 if released, 1 if deferred
	*/
	int iser_regd_buff_release(struct iser_regd_buf *regd_buf)
	{
	struct device *dma_device;

	if ((atomic_read(&regd_buf->ref_count) == 0) \|\|
	atomic_dec_and_test(&regd_buf->ref_count)) {
	/* if we used the dma mr, unreg is just NOP */
	if (regd_buf->reg.rkey != 0)
	iser_unreg_mem(&regd_buf->reg);

	if (regd_buf->dma_addr) {
	dma_device = regd_buf->device->ib_device->dma_device;
	dma_unmap_single(dma_device,
	regd_buf->dma_addr,
	regd_buf->data_size,
	regd_buf->direction);
	}
	/* else this regd buf is associated with task which we */
	/* dma_unmap_single/sg later */
	return 0;
	} else {
	iser_dbg("Release deferred, regd.buff: 0x%p\n", regd_buf);
	return 1;
	}
	}

	/**
	* iser_reg_single - fills registered buffer descriptor with
	* registration information
	*/
	void iser_reg_single(struct iser_device *device,
	struct iser_regd_buf *regd_buf,
	enum dma_data_direction direction)
	{
	dma_addr_t dma_addr;

	dma_addr = dma_map_single(device->ib_device->dma_device,
	regd_buf->virt_addr,
	regd_buf->data_size, direction);
	BUG_ON(dma_mapping_error(dma_addr));

	regd_buf->reg.lkey = device->mr->lkey;
	regd_buf->reg.rkey = 0; /* indicate there's no need to unreg */
	regd_buf->reg.len = regd_buf->data_size;
	regd_buf->reg.va = dma_addr;

	regd_buf->dma_addr = dma_addr;
	regd_buf->direction = direction;
	}

	/**
	* iser_start_rdma_unaligned_sg
	*/
	int iser_start_rdma_unaligned_sg(struct iscsi_iser_cmd_task *iser_ctask,
	enum iser_data_dir cmd_dir)
	{
	int dma_nents;
	struct device *dma_device;
	char *mem = NULL;
	struct iser_data_buf *data = &iser_ctask->data[cmd_dir];
	unsigned long cmd_data_len = data->data_len;

	if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
	mem = (void *)__get_free_pages(GFP_NOIO,
	long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
	else
	mem = kmalloc(cmd_data_len, GFP_NOIO);

	if (mem == NULL) {
	iser_err("Failed to allocate mem size %d %d for copying sglist\n",
	data->size,(int)cmd_data_len);
	return -ENOMEM;
	}

	if (cmd_dir == ISER_DIR_OUT) {
	/* copy the unaligned sg the buffer which is used for RDMA */
	struct scatterlist sg = (struct scatterlist )data->buf;
	int i;
	char p, from;

	for (p = mem, i = 0; i < data->size; i++) {
	from = kmap_atomic(sg[i].page, KM_USER0);
	memcpy(p,
	from + sg[i].offset,
	sg[i].length);
	kunmap_atomic(from, KM_USER0);
	p += sg[i].length;
	}
	}

	sg_init_one(&iser_ctask->data_copy[cmd_dir].sg_single, mem, cmd_data_len);
	iser_ctask->data_copy[cmd_dir].buf =
	&iser_ctask->data_copy[cmd_dir].sg_single;
	iser_ctask->data_copy[cmd_dir].size = 1;

	iser_ctask->data_copy[cmd_dir].copy_buf = mem;

	dma_device = iser_ctask->iser_conn->ib_conn->device->ib_device->dma_device;

	if (cmd_dir == ISER_DIR_OUT)
	dma_nents = dma_map_sg(dma_device,
	&iser_ctask->data_copy[cmd_dir].sg_single,
	1, DMA_TO_DEVICE);
	else
	dma_nents = dma_map_sg(dma_device,
	&iser_ctask->data_copy[cmd_dir].sg_single,
	1, DMA_FROM_DEVICE);

	BUG_ON(dma_nents == 0);

	iser_ctask->data_copy[cmd_dir].dma_nents = dma_nents;
	return 0;
	}

	/**
	* iser_finalize_rdma_unaligned_sg
	*/
	void iser_finalize_rdma_unaligned_sg(struct iscsi_iser_cmd_task *iser_ctask,
	enum iser_data_dir cmd_dir)
	{
	struct device *dma_device;
	struct iser_data_buf *mem_copy;
	unsigned long cmd_data_len;

	dma_device = iser_ctask->iser_conn->ib_conn->device->ib_device->dma_device;
	mem_copy = &iser_ctask->data_copy[cmd_dir];

	if (cmd_dir == ISER_DIR_OUT)
	dma_unmap_sg(dma_device, &mem_copy->sg_single, 1,
	DMA_TO_DEVICE);
	else
	dma_unmap_sg(dma_device, &mem_copy->sg_single, 1,
	DMA_FROM_DEVICE);

	if (cmd_dir == ISER_DIR_IN) {
	char *mem;
	struct scatterlist *sg;
	unsigned char p, to;
	unsigned int sg_size;
	int i;

	/* copy back read RDMA to unaligned sg */
	mem = mem_copy->copy_buf;

	sg = (struct scatterlist *)iser_ctask->data[ISER_DIR_IN].buf;
	sg_size = iser_ctask->data[ISER_DIR_IN].size;

	for (p = mem, i = 0; i < sg_size; i++){
	to = kmap_atomic(sg[i].page, KM_SOFTIRQ0);
	memcpy(to + sg[i].offset,
	p,
	sg[i].length);
	kunmap_atomic(to, KM_SOFTIRQ0);
	p += sg[i].length;
	}
	}

	cmd_data_len = iser_ctask->data[cmd_dir].data_len;

	if (cmd_data_len > ISER_KMALLOC_THRESHOLD)
	free_pages((unsigned long)mem_copy->copy_buf,
	long_log2(roundup_pow_of_two(cmd_data_len)) - PAGE_SHIFT);
	else
	kfree(mem_copy->copy_buf);

	mem_copy->copy_buf = NULL;
	}

	/**
	* iser_sg_to_page_vec - Translates scatterlist entries to physical addresses
	* and returns the length of resulting physical address array (may be less than
	* the original due to possible compaction).
	*
	* we build a "page vec" under the assumption that the SG meets the RDMA
	* alignment requirements. Other then the first and last SG elements, all
	* the "internal" elements can be compacted into a list whose elements are
	* dma addresses of physical pages. The code supports also the weird case
	* where --few fragments of the same page-- are present in the SG as
	* consecutive elements. Also, it handles one entry SG.
	*/
	static int iser_sg_to_page_vec(struct iser_data_buf *data,
	struct iser_page_vec *page_vec)
	{
	struct scatterlist sg = (struct scatterlist )data->buf;
	dma_addr_t first_addr, last_addr, page;
	int start_aligned, end_aligned;
	unsigned int cur_page = 0;
	unsigned long total_sz = 0;
	int i;

	/* compute the offset of first element */
	page_vec->offset = (u64) sg[0].offset;

	for (i = 0; i < data->dma_nents; i++) {
	total_sz += sg_dma_len(&sg[i]);

	first_addr = sg_dma_address(&sg[i]);
	last_addr = first_addr + sg_dma_len(&sg[i]);

	start_aligned = !(first_addr & ~PAGE_MASK);
	end_aligned = !(last_addr & ~PAGE_MASK);

	/* continue to collect page fragments till aligned or SG ends */
	while (!end_aligned && (i + 1 < data->dma_nents)) {
	i++;
	total_sz += sg_dma_len(&sg[i]);
	last_addr = sg_dma_address(&sg[i]) + sg_dma_len(&sg[i]);
	end_aligned = !(last_addr & ~PAGE_MASK);
	}

	first_addr = first_addr & PAGE_MASK;

	for (page = first_addr; page < last_addr; page += PAGE_SIZE)
	page_vec->pages[cur_page++] = page;

	}
	page_vec->data_size = total_sz;
	iser_dbg("page_vec->data_size:%d cur_page %d\n", page_vec->data_size,cur_page);
	return cur_page;
	}

	#define MASK_4K ((1UL << 12) - 1) /* 0xFFF */
	#define IS_4K_ALIGNED(addr) ((((unsigned long)addr) & MASK_4K) == 0)

	/**
	* iser_data_buf_aligned_len - Tries to determine the maximal correctly aligned
	* for RDMA sub-list of a scatter-gather list of memory buffers, and returns
	* the number of entries which are aligned correctly. Supports the case where
	* consecutive SG elements are actually fragments of the same physcial page.
	*/
	static unsigned int iser_data_buf_aligned_len(struct iser_data_buf *data)
	{
	struct scatterlist *sg;
	dma_addr_t end_addr, next_addr;
	int i, cnt;
	unsigned int ret_len = 0;

	sg = (struct scatterlist *)data->buf;

	for (cnt = 0, i = 0; i < data->dma_nents; i++, cnt++) {
	/* iser_dbg("Checking sg iobuf [%d]: phys=0x%08lX "
	"offset: %ld sz: %ld\n", i,
	(unsigned long)page_to_phys(sg[i].page),
	(unsigned long)sg[i].offset,
	(unsigned long)sg[i].length); */
	end_addr = sg_dma_address(&sg[i]) +
	sg_dma_len(&sg[i]);
	/* iser_dbg("Checking sg iobuf end address "
	"0x%08lX\n", end_addr); */
	if (i + 1 < data->dma_nents) {
	next_addr = sg_dma_address(&sg[i+1]);
	/* are i, i+1 fragments of the same page? */
	if (end_addr == next_addr)
	continue;
	else if (!IS_4K_ALIGNED(end_addr)) {
	ret_len = cnt + 1;
	break;
	}
	}
	}
	if (i == data->dma_nents)
	ret_len = cnt; /* loop ended */
	iser_dbg("Found %d aligned entries out of %d in sg:0x%p\n",
	ret_len, data->dma_nents, data);
	return ret_len;
	}

	static void iser_data_buf_dump(struct iser_data_buf *data)
	{
	struct scatterlist sg = (struct scatterlist )data->buf;
	int i;

	for (i = 0; i < data->size; i++)
	iser_err("sg[%d] dma_addr:0x%lX page:0x%p "
	"off:%d sz:%d dma_len:%d\n",
	i, (unsigned long)sg_dma_address(&sg[i]),
	sg[i].page, sg[i].offset,
	sg[i].length,sg_dma_len(&sg[i]));
	}

	static void iser_dump_page_vec(struct iser_page_vec *page_vec)
	{
	int i;

	iser_err("page vec length %d data size %d\n",
	page_vec->length, page_vec->data_size);
	for (i = 0; i < page_vec->length; i++)
	iser_err("%d %lx\n",i,(unsigned long)page_vec->pages[i]);
	}

	static void iser_page_vec_build(struct iser_data_buf *data,
	struct iser_page_vec *page_vec)
	{
	int page_vec_len = 0;

	page_vec->length = 0;
	page_vec->offset = 0;

	iser_dbg("Translating sg sz: %d\n", data->dma_nents);
	page_vec_len = iser_sg_to_page_vec(data,page_vec);
	iser_dbg("sg len %d page_vec_len %d\n", data->dma_nents,page_vec_len);

	page_vec->length = page_vec_len;

	if (page_vec_len * PAGE_SIZE < page_vec->data_size) {
	iser_err("page_vec too short to hold this SG\n");
	iser_data_buf_dump(data);
	iser_dump_page_vec(page_vec);
	BUG();
	}
	}

	/**
	* iser_reg_rdma_mem - Registers memory intended for RDMA,
	* obtaining rkey and va
	*
	* returns 0 on success, errno code on failure
	*/
	int iser_reg_rdma_mem(struct iscsi_iser_cmd_task *iser_ctask,
	enum iser_data_dir cmd_dir)
	{
	struct iser_conn *ib_conn = iser_ctask->iser_conn->ib_conn;
	struct iser_data_buf *mem = &iser_ctask->data[cmd_dir];
	struct iser_regd_buf *regd_buf;
	int aligned_len;
	int err;

	regd_buf = &iser_ctask->rdma_regd[cmd_dir];

	aligned_len = iser_data_buf_aligned_len(mem);
	if (aligned_len != mem->size) {
	iser_err("rdma alignment violation %d/%d aligned\n",
	aligned_len, mem->size);
	iser_data_buf_dump(mem);
	/* allocate copy buf, if we are writing, copy the */
	/* unaligned scatterlist, dma map the copy */
	if (iser_start_rdma_unaligned_sg(iser_ctask, cmd_dir) != 0)
	return -ENOMEM;
	mem = &iser_ctask->data_copy[cmd_dir];
	}

	iser_page_vec_build(mem, ib_conn->page_vec);
	err = iser_reg_page_vec(ib_conn, ib_conn->page_vec, &regd_buf->reg);
	if (err)
	return err;

	/* take a reference on this regd buf such that it will not be released *
	* (eg in send dto completion) before we get the scsi response */
	atomic_inc(&regd_buf->ref_count);
	return 0;
	}