linux/net/rds/info.c

/*
 * 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/srcu.h>
#include <linux/slab.h>
#include <linux/proc_fs.h>
#include <linux/export.h>
#include <linux/uio.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;
};

DEFINE_STATIC_SRCU(rds_info_srcu);
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);
	if (WARN_ON_ONCE(rds_info_funcs[offset])) {
		spin_unlock(&rds_info_lock);
		return;
	}
	WRITE_ONCE(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);
	if (WARN_ON_ONCE(rds_info_funcs[offset] != func)) {
		spin_unlock(&rds_info_lock);
		return;
	}
	WRITE_ONCE(rds_info_funcs[offset], NULL);
	spin_unlock(&rds_info_lock);
	synchronize_srcu(&rds_info_srcu);
}
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\n", *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);

/*
 * @opt->iter_out describes the buffer that the information snapshot will be
 * copied into, and @opt->optlen is the size of that buffer on input.  On
 * output @opt->optlen is set to the size of the requested snapshot in bytes.
 *
 * This function returns -errno if there is a failure, particularly -ENOSPC
 * if the given 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, sockopt_t *opt)
{
	struct rds_info_iterator iter;
	struct rds_info_lengths lens;
	unsigned long nr_pages = 0;
	rds_info_func func;
	struct page **pages = NULL;
	size_t offset0 = 0;
	int srcu_idx;
	int npages = 0;
	int ret;
	int len;
	int total;

	len = opt->optlen;

	/* check for all kinds of wrapping and the like */
	if (len < 0 || len > INT_MAX - PAGE_SIZE + 1) {
		ret = -EINVAL;
		goto out;
	}

	/* The info producers write into the pages with kmap_atomic() while
	 * holding a spinlock, so they need a genuine page-backed user buffer.
	 */
	if (!user_backed_iter(&opt->iter_out)) {
		ret = -EOPNOTSUPP;
		goto out;
	}

	/* a 0 len call is just trying to probe its length */
	if (len == 0)
		goto call_func;

	/*
	 * Preallocate the page array and pass it in so that
	 * iov_iter_extract_pages() fills it in place rather than allocating
	 * one for us.  Handing it a non-NULL array keeps ownership of the
	 * array with us on every return path, instead of depending on the
	 * iterator code to allocate and hand it back.
	 */
	npages = iov_iter_npages(&opt->iter_out, INT_MAX);
	pages = kvmalloc_array(npages, sizeof(*pages), GFP_KERNEL);
	if (!pages) {
		ret = -ENOMEM;
		goto out;
	}

	ret = iov_iter_extract_pages(&opt->iter_out, &pages, len, npages,
				     0, &offset0);
	if (ret < 0)
		goto out;
	nr_pages = DIV_ROUND_UP(offset0 + ret, PAGE_SIZE);
	if (ret != len) {
		ret = -EAGAIN; /* XXX ? */
		goto out;
	}

	rdsdebug("len %d nr_pages %lu\n", len, nr_pages);

call_func:
	srcu_idx = srcu_read_lock(&rds_info_srcu);
	func = READ_ONCE(rds_info_funcs[optname - RDS_INFO_FIRST]);
	if (!func) {
		srcu_read_unlock(&rds_info_srcu, srcu_idx);
		ret = -ENOPROTOOPT;
		goto out;
	}

	iter.pages = pages;
	iter.addr = NULL;
	iter.offset = offset0;

	func(sock, len, &iter, &lens);
	srcu_read_unlock(&rds_info_srcu, srcu_idx);
	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;
	}

	opt->optlen = len;

out:
	/*
	 * iov_iter_extract_pages() pins only user-backed (ubuf) iters;
	 * iov_iter_extract_will_pin() reports whether an unpin is owed here.
	 */
	if (pages && iov_iter_extract_will_pin(&opt->iter_out))
		unpin_user_pages_dirty_lock(pages, nr_pages, true);
	kvfree(pages);

	return ret;
}