/*
 * 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);

/*
 * Message allocation uses this to build up regions of a 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\n", 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\n", 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);
}