/*
   * 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/percpu.h>
  #include <linux/seq_file.h>
  #include <linux/slab.h>
  #include <linux/proc_fs.h>
  #include <linux/export.h>
  
  #include "rds.h"
  
  /*
   * This file implements a getsockopt() call which copies a set of fixed
   * sized structs into a user-specified buffer as a means of providing
   * read-only information about RDS.
   *
   * For a given information source there are a given number of fixed sized
   * structs at a given time.  The structs are only copied if the user-specified
   * buffer is big enough.  The destination pages that make up the buffer
   * are pinned for the duration of the copy.
   *
   * This gives us the following benefits:
   *
   * - simple implementation, no copy "position" across multiple calls
   * - consistent snapshot of an info source
   * - atomic copy works well with whatever locking info source has
   * - one portable tool to get rds info across implementations
   * - long-lived tool can get info without allocating
   *
   * at the following costs:
   *
   * - info source copy must be pinned, may be "large"
   */
  
  struct rds_info_iterator {
  	struct page **pages;
  	void *addr;
  	unsigned long offset;
  };
  
  static DEFINE_SPINLOCK(rds_info_lock);
  static rds_info_func rds_info_funcs[RDS_INFO_LAST - RDS_INFO_FIRST + 1];
  
  void rds_info_register_func(int optname, rds_info_func func)
  {
  	int offset = optname - RDS_INFO_FIRST;
  
  	BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
  
  	spin_lock(&rds_info_lock);
  	BUG_ON(rds_info_funcs[offset]);
  	rds_info_funcs[offset] = func;
  	spin_unlock(&rds_info_lock);
  }
  EXPORT_SYMBOL_GPL(rds_info_register_func);
  
  void rds_info_deregister_func(int optname, rds_info_func func)
  {
  	int offset = optname - RDS_INFO_FIRST;
  
  	BUG_ON(optname < RDS_INFO_FIRST || optname > RDS_INFO_LAST);
  
  	spin_lock(&rds_info_lock);
  	BUG_ON(rds_info_funcs[offset] != func);
  	rds_info_funcs[offset] = NULL;
  	spin_unlock(&rds_info_lock);
  }
  EXPORT_SYMBOL_GPL(rds_info_deregister_func);
  
  /*
   * Typically we hold an atomic kmap across multiple rds_info_copy() calls
   * because the kmap is so expensive.  This must be called before using blocking
   * operations while holding the mapping and as the iterator is torn down.
   */
  void rds_info_iter_unmap(struct rds_info_iterator *iter)
  {
  	if (iter->addr) {
  		kunmap_atomic(iter->addr);
  		iter->addr = NULL;
  	}
  }
  
  /*
   * get_user_pages() called flush_dcache_page() on the pages for us.
   */
  void rds_info_copy(struct rds_info_iterator *iter, void *data,
  		   unsigned long bytes)
  {
  	unsigned long this;
  
  	while (bytes) {
  		if (!iter->addr)
  			iter->addr = kmap_atomic(*iter->pages);
  
  		this = min(bytes, PAGE_SIZE - iter->offset);
  
  		rdsdebug("page %p addr %p offset %lu this %lu data %p "
  			  "bytes %lu
  ", *iter->pages, iter->addr,
  			  iter->offset, this, data, bytes);
  
  		memcpy(iter->addr + iter->offset, data, this);
  
  		data += this;
  		bytes -= this;
  		iter->offset += this;
  
  		if (iter->offset == PAGE_SIZE) {
  			kunmap_atomic(iter->addr);
  			iter->addr = NULL;
  			iter->offset = 0;
  			iter->pages++;
  		}
  	}
  }
  EXPORT_SYMBOL_GPL(rds_info_copy);
  
  /*
   * @optval points to the userspace buffer that the information snapshot
   * will be copied into.
   *
   * @optlen on input is the size of the buffer in userspace.  @optlen
   * on output is the size of the requested snapshot in bytes.
   *
   * This function returns -errno if there is a failure, particularly -ENOSPC
   * if the given userspace buffer was not large enough to fit the snapshot.
   * On success it returns the positive number of bytes of each array element
   * in the snapshot.
   */
  int rds_info_getsockopt(struct socket *sock, int optname, char __user *optval,
  			int __user *optlen)
  {
  	struct rds_info_iterator iter;
  	struct rds_info_lengths lens;
  	unsigned long nr_pages = 0;
  	unsigned long start;
  	unsigned long i;
  	rds_info_func func;
  	struct page **pages = NULL;
  	int ret;
  	int len;
  	int total;
  
  	if (get_user(len, optlen)) {
  		ret = -EFAULT;
  		goto out;
  	}
  
  	/* check for all kinds of wrapping and the like */
  	start = (unsigned long)optval;
  	if (len < 0 || len + PAGE_SIZE - 1 < len || start + len < start) {
  		ret = -EINVAL;
  		goto out;
  	}
  
  	/* a 0 len call is just trying to probe its length */
  	if (len == 0)
  		goto call_func;
  
  	nr_pages = (PAGE_ALIGN(start + len) - (start & PAGE_MASK))
  			>> PAGE_SHIFT;
  
  	pages = kmalloc(nr_pages * sizeof(struct page *), GFP_KERNEL);
  	if (!pages) {
  		ret = -ENOMEM;
  		goto out;
  	}
  	ret = get_user_pages_fast(start, nr_pages, 1, pages);
  	if (ret != nr_pages) {
  		if (ret > 0)
  			nr_pages = ret;
  		else
  			nr_pages = 0;
  		ret = -EAGAIN; /* XXX ? */
  		goto out;
  	}
  
  	rdsdebug("len %d nr_pages %lu
  ", len, nr_pages);
  
  call_func:
  	func = rds_info_funcs[optname - RDS_INFO_FIRST];
  	if (!func) {
  		ret = -ENOPROTOOPT;
  		goto out;
  	}
  
  	iter.pages = pages;
  	iter.addr = NULL;
  	iter.offset = start & (PAGE_SIZE - 1);
  
  	func(sock, len, &iter, &lens);
  	BUG_ON(lens.each == 0);
  
  	total = lens.nr * lens.each;
  
  	rds_info_iter_unmap(&iter);
  
  	if (total > len) {
  		len = total;
  		ret = -ENOSPC;
  	} else {
  		len = total;
  		ret = lens.each;
  	}
  
  	if (put_user(len, optlen))
  		ret = -EFAULT;
  
  out:
  	for (i = 0; pages && i < nr_pages; i++)
  		put_page(pages[i]);
  	kfree(pages);
  
  	return ret;
  }