info.c

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/*
 * 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\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);

/*
 * @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\n", 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;
}