/*
 * Copyright (C) 2006-2009 Red Hat, Inc.
 *
 * This file is released under the LGPL.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/workqueue.h>
#include <linux/connector.h>
#include <linux/device-mapper.h>
#include <linux/dm-log-userspace.h>

#include "dm-log-userspace-transfer.h"

static uint32_t dm_ulog_seq;

/*
 * Netlink/Connector is an unreliable protocol.  How long should
 * we wait for a response before assuming it was lost and retrying?
 * (If we do receive a response after this time, it will be discarded
 * and the response to the resent request will be waited for.
 */
#define DM_ULOG_RETRY_TIMEOUT (15 * HZ)

/*
 * Pre-allocated space for speed
 */
#define DM_ULOG_PREALLOCED_SIZE 512
static struct cn_msg *prealloced_cn_msg;
static struct dm_ulog_request *prealloced_ulog_tfr;

static struct cb_id ulog_cn_id = {
        .idx = CN_IDX_DM,
        .val = CN_VAL_DM_USERSPACE_LOG
};

static DEFINE_MUTEX(dm_ulog_lock);

struct receiving_pkg {
        struct list_head list;
        struct completion complete;

        uint32_t seq;

        int error;
        size_t *data_size;
        char *data;
};

static DEFINE_SPINLOCK(receiving_list_lock);
static struct list_head receiving_list;

static int dm_ulog_sendto_server(struct dm_ulog_request *tfr)
{
        int r;
        struct cn_msg *msg = prealloced_cn_msg;

        memset(msg, 0, sizeof(struct cn_msg));

        msg->id.idx = ulog_cn_id.idx;
        msg->id.val = ulog_cn_id.val;
        msg->ack = 0;
        msg->seq = tfr->seq;
        msg->len = sizeof(struct dm_ulog_request) + tfr->data_size;

        r = cn_netlink_send(msg, 0, gfp_any());

        return r;
}

/*
 * Parameters for this function can be either msg or tfr, but not
 * both.  This function fills in the reply for a waiting request.
 * If just msg is given, then the reply is simply an ACK from userspace
 * that the request was received.
 *
 * Returns: 0 on success, -ENOENT on failure
 */
static int fill_pkg(struct cn_msg *msg, struct dm_ulog_request *tfr)
{
        uint32_t rtn_seq = (msg) ? msg->seq : (tfr) ? tfr->seq : 0;
        struct receiving_pkg *pkg;

        /*
         * The 'receiving_pkg' entries in this list are statically
         * allocated on the stack in 'dm_consult_userspace'.
         * Each process that is waiting for a reply from the user
         * space server will have an entry in this list.
         *
         * We are safe to do it this way because the stack space
         * is unique to each process, but still addressable by
         * other processes.
         */
        list_for_each_entry(pkg, &receiving_list, list) {
                if (rtn_seq != pkg->seq)
                        continue;

                if (msg) {
                        pkg->error = -msg->ack;
                        /*
                         * If we are trying again, we will need to know our
                         * storage capacity.  Otherwise, along with the
                         * error code, we make explicit that we have no data.
                         */
                        if (pkg->error != -EAGAIN)
                                *(pkg->data_size) = 0;
                } else if (tfr->data_size > *(pkg->data_size)) {
                        DMERR("Insufficient space to receive package [%u] "
                              "(%u vs %zu)", tfr->request_type,
                              tfr->data_size, *(pkg->data_size));

                        *(pkg->data_size) = 0;
                        pkg->error = -ENOSPC;
                } else {
                        pkg->error = tfr->error;
                        memcpy(pkg->data, tfr->data, tfr->data_size);
                        *(pkg->data_size) = tfr->data_size;
                }
                complete(&pkg->complete);
                return 0;
        }

        return -ENOENT;
}

/*
 * This is the connector callback that delivers data
 * that was sent from userspace.
 */
static void cn_ulog_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
{
        struct dm_ulog_request *tfr = (struct dm_ulog_request *)(msg + 1);

        if (!cap_raised(current_cap(), CAP_SYS_ADMIN))
                return;

        spin_lock(&receiving_list_lock);
        if (msg->len == 0)
                fill_pkg(msg, NULL);
        else if (msg->len < sizeof(*tfr))
                DMERR("Incomplete message received (expected %u, got %u): [%u]",
                      (unsigned)sizeof(*tfr), msg->len, msg->seq);
        else
                fill_pkg(NULL, tfr);
        spin_unlock(&receiving_list_lock);
}

/**
 * dm_consult_userspace
 * @uuid: log's universal unique identifier (must be DM_UUID_LEN in size)
 * @luid: log's local unique identifier
 * @request_type:  found in include/linux/dm-log-userspace.h
 * @data: data to tx to the server
 * @data_size: size of data in bytes
 * @rdata: place to put return data from server
 * @rdata_size: value-result (amount of space given/amount of space used)
 *
 * rdata_size is undefined on failure.
 *
 * Memory used to communicate with userspace is zero'ed
 * before populating to ensure that no unwanted bits leak
 * from kernel space to user-space.  All userspace log communications
 * between kernel and user space go through this function.
 *
 * Returns: 0 on success, -EXXX on failure
 **/
int dm_consult_userspace(const char *uuid, uint64_t luid, int request_type,
                         char *data, size_t data_size,
                         char *rdata, size_t *rdata_size)
{
        int r = 0;
        size_t dummy = 0;
        int overhead_size = sizeof(struct dm_ulog_request) + sizeof(struct cn_msg);
        struct dm_ulog_request *tfr = prealloced_ulog_tfr;
        struct receiving_pkg pkg;

        /*
         * Given the space needed to hold the 'struct cn_msg' and
         * 'struct dm_ulog_request' - do we have enough payload
         * space remaining?
         */
        if (data_size > (DM_ULOG_PREALLOCED_SIZE - overhead_size)) {
                DMINFO("Size of tfr exceeds preallocated size");
                return -EINVAL;
        }

        if (!rdata_size)
                rdata_size = &dummy;
resend:
        /*
         * We serialize the sending of requests so we can
         * use the preallocated space.
         */
        mutex_lock(&dm_ulog_lock);

        memset(tfr, 0, DM_ULOG_PREALLOCED_SIZE - sizeof(struct cn_msg));
        memcpy(tfr->uuid, uuid, DM_UUID_LEN);
        tfr->version = DM_ULOG_REQUEST_VERSION;
        tfr->luid = luid;
        tfr->seq = dm_ulog_seq++;

        /*
         * Must be valid request type (all other bits set to
         * zero).  This reserves other bits for possible future
         * use.
         */
        tfr->request_type = request_type & DM_ULOG_REQUEST_MASK;

        tfr->data_size = data_size;
        if (data && data_size)
                memcpy(tfr->data, data, data_size);

        memset(&pkg, 0, sizeof(pkg));
        init_completion(&pkg.complete);
        pkg.seq = tfr->seq;
        pkg.data_size = rdata_size;
        pkg.data = rdata;
        spin_lock(&receiving_list_lock);
        list_add(&(pkg.list), &receiving_list);
        spin_unlock(&receiving_list_lock);

        r = dm_ulog_sendto_server(tfr);

        mutex_unlock(&dm_ulog_lock);

        if (r) {
                DMERR("Unable to send log request [%u] to userspace: %d",
                      request_type, r);
                spin_lock(&receiving_list_lock);
                list_del_init(&(pkg.list));
                spin_unlock(&receiving_list_lock);

                goto out;
        }

        r = wait_for_completion_timeout(&(pkg.complete), DM_ULOG_RETRY_TIMEOUT);
        spin_lock(&receiving_list_lock);
        list_del_init(&(pkg.list));
        spin_unlock(&receiving_list_lock);
        if (!r) {
                DMWARN("[%s] Request timed out: [%u/%u] - retrying",
                       (strlen(uuid) > 8) ?
                       (uuid + (strlen(uuid) - 8)) : (uuid),
                       request_type, pkg.seq);
                goto resend;
        }

        r = pkg.error;
        if (r == -EAGAIN)
                goto resend;

out:
        return r;
}

int dm_ulog_tfr_init(void)
{
        int r;
        void *prealloced;

        INIT_LIST_HEAD(&receiving_list);

        prealloced = kmalloc(DM_ULOG_PREALLOCED_SIZE, GFP_KERNEL);
        if (!prealloced)
                return -ENOMEM;

        prealloced_cn_msg = prealloced;
        prealloced_ulog_tfr = prealloced + sizeof(struct cn_msg);

        r = cn_add_callback(&ulog_cn_id, "dmlogusr", cn_ulog_callback);
        if (r) {
                cn_del_callback(&ulog_cn_id);
                return r;
        }

        return 0;
}

void dm_ulog_tfr_exit(void)
{
        cn_del_callback(&ulog_cn_id);
        kfree(prealloced_cn_msg);
}