dm-log-userspace-transfer.c

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/*
 * 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 (!capable(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);
}

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);
}