/*
   * Copyright (c) 2006 Oracle.  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.
   *
   */
  #include <linux/highmem.h>
  #include <linux/gfp.h>
  #include <linux/cpu.h>
  #include <linux/export.h>
  
  #include "rds.h"
  
  struct rds_page_remainder {
  	struct page	*r_page;
  	unsigned long	r_offset;
  };
  
  static DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder,
  				     rds_page_remainders);
  
  /*
   * returns 0 on success or -errno on failure.
   *
   * We don't have to worry about flush_dcache_page() as this only works
   * with private pages.  If, say, we were to do directed receive to pinned
   * user pages we'd have to worry more about cache coherence.  (Though
   * the flush_dcache_page() in get_user_pages() would probably be enough).
   */
  int rds_page_copy_user(struct page *page, unsigned long offset,
  		       void __user *ptr, unsigned long bytes,
  		       int to_user)
  {
  	unsigned long ret;
  	void *addr;
  
  	addr = kmap(page);
  	if (to_user) {
  		rds_stats_add(s_copy_to_user, bytes);
  		ret = copy_to_user(ptr, addr + offset, bytes);
  	} else {
  		rds_stats_add(s_copy_from_user, bytes);
  		ret = copy_from_user(addr + offset, ptr, bytes);
  	}
  	kunmap(page);
  
  	return ret ? -EFAULT : 0;
  }
  EXPORT_SYMBOL_GPL(rds_page_copy_user);
  
  /**
   * rds_page_remainder_alloc - build up regions of a message.
   *
   * @scat: Scatter list for message
   * @bytes: the number of bytes needed.
   * @gfp: the waiting behaviour of the allocation
   *
   * @gfp is always ored with __GFP_HIGHMEM.  Callers must be prepared to
   * kmap the pages, etc.
   *
   * If @bytes is at least a full page then this just returns a page from
   * alloc_page().
   *
   * If @bytes is a partial page then this stores the unused region of the
   * page in a per-cpu structure.  Future partial-page allocations may be
   * satisfied from that cached region.  This lets us waste less memory on
   * small allocations with minimal complexity.  It works because the transmit
   * path passes read-only page regions down to devices.  They hold a page
   * reference until they are done with the region.
   */
  int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes,
  			     gfp_t gfp)
  {
  	struct rds_page_remainder *rem;
  	unsigned long flags;
  	struct page *page;
  	int ret;
  
  	gfp |= __GFP_HIGHMEM;
  
  	/* jump straight to allocation if we're trying for a huge page */
  	if (bytes >= PAGE_SIZE) {
  		page = alloc_page(gfp);
  		if (!page) {
  			ret = -ENOMEM;
  		} else {
  			sg_set_page(scat, page, PAGE_SIZE, 0);
  			ret = 0;
  		}
  		goto out;
  	}
  
  	rem = &per_cpu(rds_page_remainders, get_cpu());
  	local_irq_save(flags);
  
  	while (1) {
  		/* avoid a tiny region getting stuck by tossing it */
  		if (rem->r_page && bytes > (PAGE_SIZE - rem->r_offset)) {
  			rds_stats_inc(s_page_remainder_miss);
  			__free_page(rem->r_page);
  			rem->r_page = NULL;
  		}
  
  		/* hand out a fragment from the cached page */
  		if (rem->r_page && bytes <= (PAGE_SIZE - rem->r_offset)) {
  			sg_set_page(scat, rem->r_page, bytes, rem->r_offset);
  			get_page(sg_page(scat));
  
  			if (rem->r_offset != 0)
  				rds_stats_inc(s_page_remainder_hit);
  
  			rem->r_offset += bytes;
  			if (rem->r_offset == PAGE_SIZE) {
  				__free_page(rem->r_page);
  				rem->r_page = NULL;
  			}
  			ret = 0;
  			break;
  		}
  
  		/* alloc if there is nothing for us to use */
  		local_irq_restore(flags);
  		put_cpu();
  
  		page = alloc_page(gfp);
  
  		rem = &per_cpu(rds_page_remainders, get_cpu());
  		local_irq_save(flags);
  
  		if (!page) {
  			ret = -ENOMEM;
  			break;
  		}
  
  		/* did someone race to fill the remainder before us? */
  		if (rem->r_page) {
  			__free_page(page);
  			continue;
  		}
  
  		/* otherwise install our page and loop around to alloc */
  		rem->r_page = page;
  		rem->r_offset = 0;
  	}
  
  	local_irq_restore(flags);
  	put_cpu();
  out:
  	rdsdebug("bytes %lu ret %d %p %u %u
  ", bytes, ret,
  		 ret ? NULL : sg_page(scat), ret ? 0 : scat->offset,
  		 ret ? 0 : scat->length);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(rds_page_remainder_alloc);
  
  static int rds_page_remainder_cpu_notify(struct notifier_block *self,
  					 unsigned long action, void *hcpu)
  {
  	struct rds_page_remainder *rem;
  	long cpu = (long)hcpu;
  
  	rem = &per_cpu(rds_page_remainders, cpu);
  
  	rdsdebug("cpu %ld action 0x%lx
  ", cpu, action);
  
  	switch (action) {
  	case CPU_DEAD:
  		if (rem->r_page)
  			__free_page(rem->r_page);
  		rem->r_page = NULL;
  		break;
  	}
  
  	return 0;
  }
  
  static struct notifier_block rds_page_remainder_nb = {
  	.notifier_call = rds_page_remainder_cpu_notify,
  };
  
  void rds_page_exit(void)
  {
  	int i;
  
  	for_each_possible_cpu(i)
  		rds_page_remainder_cpu_notify(&rds_page_remainder_nb,
  					      (unsigned long)CPU_DEAD,
  					      (void *)(long)i);
  }