linux/drivers/md/dm-log-userspace-transfer.c
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   1/*
   2 * Copyright (C) 2006-2009 Red Hat, Inc.
   3 *
   4 * This file is released under the LGPL.
   5 */
   6
   7#include <linux/kernel.h>
   8#include <linux/module.h>
   9#include <linux/slab.h>
  10#include <net/sock.h>
  11#include <linux/workqueue.h>
  12#include <linux/connector.h>
  13#include <linux/device-mapper.h>
  14#include <linux/dm-log-userspace.h>
  15
  16#include "dm-log-userspace-transfer.h"
  17
  18static uint32_t dm_ulog_seq;
  19
  20/*
  21 * Netlink/Connector is an unreliable protocol.  How long should
  22 * we wait for a response before assuming it was lost and retrying?
  23 * (If we do receive a response after this time, it will be discarded
  24 * and the response to the resent request will be waited for.
  25 */
  26#define DM_ULOG_RETRY_TIMEOUT (15 * HZ)
  27
  28/*
  29 * Pre-allocated space for speed
  30 */
  31#define DM_ULOG_PREALLOCED_SIZE 512
  32static struct cn_msg *prealloced_cn_msg;
  33static struct dm_ulog_request *prealloced_ulog_tfr;
  34
  35static struct cb_id ulog_cn_id = {
  36        .idx = CN_IDX_DM,
  37        .val = CN_VAL_DM_USERSPACE_LOG
  38};
  39
  40static DEFINE_MUTEX(dm_ulog_lock);
  41
  42struct receiving_pkg {
  43        struct list_head list;
  44        struct completion complete;
  45
  46        uint32_t seq;
  47
  48        int error;
  49        size_t *data_size;
  50        char *data;
  51};
  52
  53static DEFINE_SPINLOCK(receiving_list_lock);
  54static struct list_head receiving_list;
  55
  56static int dm_ulog_sendto_server(struct dm_ulog_request *tfr)
  57{
  58        int r;
  59        struct cn_msg *msg = prealloced_cn_msg;
  60
  61        memset(msg, 0, sizeof(struct cn_msg));
  62
  63        msg->id.idx = ulog_cn_id.idx;
  64        msg->id.val = ulog_cn_id.val;
  65        msg->ack = 0;
  66        msg->seq = tfr->seq;
  67        msg->len = sizeof(struct dm_ulog_request) + tfr->data_size;
  68
  69        r = cn_netlink_send(msg, 0, gfp_any());
  70
  71        return r;
  72}
  73
  74/*
  75 * Parameters for this function can be either msg or tfr, but not
  76 * both.  This function fills in the reply for a waiting request.
  77 * If just msg is given, then the reply is simply an ACK from userspace
  78 * that the request was received.
  79 *
  80 * Returns: 0 on success, -ENOENT on failure
  81 */
  82static int fill_pkg(struct cn_msg *msg, struct dm_ulog_request *tfr)
  83{
  84        uint32_t rtn_seq = (msg) ? msg->seq : (tfr) ? tfr->seq : 0;
  85        struct receiving_pkg *pkg;
  86
  87        /*
  88         * The 'receiving_pkg' entries in this list are statically
  89         * allocated on the stack in 'dm_consult_userspace'.
  90         * Each process that is waiting for a reply from the user
  91         * space server will have an entry in this list.
  92         *
  93         * We are safe to do it this way because the stack space
  94         * is unique to each process, but still addressable by
  95         * other processes.
  96         */
  97        list_for_each_entry(pkg, &receiving_list, list) {
  98                if (rtn_seq != pkg->seq)
  99                        continue;
 100
 101                if (msg) {
 102                        pkg->error = -msg->ack;
 103                        /*
 104                         * If we are trying again, we will need to know our
 105                         * storage capacity.  Otherwise, along with the
 106                         * error code, we make explicit that we have no data.
 107                         */
 108                        if (pkg->error != -EAGAIN)
 109                                *(pkg->data_size) = 0;
 110                } else if (tfr->data_size > *(pkg->data_size)) {
 111                        DMERR("Insufficient space to receive package [%u] "
 112                              "(%u vs %zu)", tfr->request_type,
 113                              tfr->data_size, *(pkg->data_size));
 114
 115                        *(pkg->data_size) = 0;
 116                        pkg->error = -ENOSPC;
 117                } else {
 118                        pkg->error = tfr->error;
 119                        memcpy(pkg->data, tfr->data, tfr->data_size);
 120                        *(pkg->data_size) = tfr->data_size;
 121                }
 122                complete(&pkg->complete);
 123                return 0;
 124        }
 125
 126        return -ENOENT;
 127}
 128
 129/*
 130 * This is the connector callback that delivers data
 131 * that was sent from userspace.
 132 */
 133static void cn_ulog_callback(struct cn_msg *msg, struct netlink_skb_parms *nsp)
 134{
 135        struct dm_ulog_request *tfr = (struct dm_ulog_request *)(msg + 1);
 136
 137        if (!capable(CAP_SYS_ADMIN))
 138                return;
 139
 140        spin_lock(&receiving_list_lock);
 141        if (msg->len == 0)
 142                fill_pkg(msg, NULL);
 143        else if (msg->len < sizeof(*tfr))
 144                DMERR("Incomplete message received (expected %u, got %u): [%u]",
 145                      (unsigned)sizeof(*tfr), msg->len, msg->seq);
 146        else
 147                fill_pkg(NULL, tfr);
 148        spin_unlock(&receiving_list_lock);
 149}
 150
 151/**
 152 * dm_consult_userspace
 153 * @uuid: log's universal unique identifier (must be DM_UUID_LEN in size)
 154 * @luid: log's local unique identifier
 155 * @request_type:  found in include/linux/dm-log-userspace.h
 156 * @data: data to tx to the server
 157 * @data_size: size of data in bytes
 158 * @rdata: place to put return data from server
 159 * @rdata_size: value-result (amount of space given/amount of space used)
 160 *
 161 * rdata_size is undefined on failure.
 162 *
 163 * Memory used to communicate with userspace is zero'ed
 164 * before populating to ensure that no unwanted bits leak
 165 * from kernel space to user-space.  All userspace log communications
 166 * between kernel and user space go through this function.
 167 *
 168 * Returns: 0 on success, -EXXX on failure
 169 **/
 170int dm_consult_userspace(const char *uuid, uint64_t luid, int request_type,
 171                         char *data, size_t data_size,
 172                         char *rdata, size_t *rdata_size)
 173{
 174        int r = 0;
 175        size_t dummy = 0;
 176        int overhead_size = sizeof(struct dm_ulog_request) + sizeof(struct cn_msg);
 177        struct dm_ulog_request *tfr = prealloced_ulog_tfr;
 178        struct receiving_pkg pkg;
 179
 180        /*
 181         * Given the space needed to hold the 'struct cn_msg' and
 182         * 'struct dm_ulog_request' - do we have enough payload
 183         * space remaining?
 184         */
 185        if (data_size > (DM_ULOG_PREALLOCED_SIZE - overhead_size)) {
 186                DMINFO("Size of tfr exceeds preallocated size");
 187                return -EINVAL;
 188        }
 189
 190        if (!rdata_size)
 191                rdata_size = &dummy;
 192resend:
 193        /*
 194         * We serialize the sending of requests so we can
 195         * use the preallocated space.
 196         */
 197        mutex_lock(&dm_ulog_lock);
 198
 199        memset(tfr, 0, DM_ULOG_PREALLOCED_SIZE - sizeof(struct cn_msg));
 200        memcpy(tfr->uuid, uuid, DM_UUID_LEN);
 201        tfr->version = DM_ULOG_REQUEST_VERSION;
 202        tfr->luid = luid;
 203        tfr->seq = dm_ulog_seq++;
 204
 205        /*
 206         * Must be valid request type (all other bits set to
 207         * zero).  This reserves other bits for possible future
 208         * use.
 209         */
 210        tfr->request_type = request_type & DM_ULOG_REQUEST_MASK;
 211
 212        tfr->data_size = data_size;
 213        if (data && data_size)
 214                memcpy(tfr->data, data, data_size);
 215
 216        memset(&pkg, 0, sizeof(pkg));
 217        init_completion(&pkg.complete);
 218        pkg.seq = tfr->seq;
 219        pkg.data_size = rdata_size;
 220        pkg.data = rdata;
 221        spin_lock(&receiving_list_lock);
 222        list_add(&(pkg.list), &receiving_list);
 223        spin_unlock(&receiving_list_lock);
 224
 225        r = dm_ulog_sendto_server(tfr);
 226
 227        mutex_unlock(&dm_ulog_lock);
 228
 229        if (r) {
 230                DMERR("Unable to send log request [%u] to userspace: %d",
 231                      request_type, r);
 232                spin_lock(&receiving_list_lock);
 233                list_del_init(&(pkg.list));
 234                spin_unlock(&receiving_list_lock);
 235
 236                goto out;
 237        }
 238
 239        r = wait_for_completion_timeout(&(pkg.complete), DM_ULOG_RETRY_TIMEOUT);
 240        spin_lock(&receiving_list_lock);
 241        list_del_init(&(pkg.list));
 242        spin_unlock(&receiving_list_lock);
 243        if (!r) {
 244                DMWARN("[%s] Request timed out: [%u/%u] - retrying",
 245                       (strlen(uuid) > 8) ?
 246                       (uuid + (strlen(uuid) - 8)) : (uuid),
 247                       request_type, pkg.seq);
 248                goto resend;
 249        }
 250
 251        r = pkg.error;
 252        if (r == -EAGAIN)
 253                goto resend;
 254
 255out:
 256        return r;
 257}
 258
 259int dm_ulog_tfr_init(void)
 260{
 261        int r;
 262        void *prealloced;
 263
 264        INIT_LIST_HEAD(&receiving_list);
 265
 266        prealloced = kmalloc(DM_ULOG_PREALLOCED_SIZE, GFP_KERNEL);
 267        if (!prealloced)
 268                return -ENOMEM;
 269
 270        prealloced_cn_msg = prealloced;
 271        prealloced_ulog_tfr = prealloced + sizeof(struct cn_msg);
 272
 273        r = cn_add_callback(&ulog_cn_id, "dmlogusr", cn_ulog_callback);
 274        if (r) {
 275                cn_del_callback(&ulog_cn_id);
 276                return r;
 277        }
 278
 279        return 0;
 280}
 281
 282void dm_ulog_tfr_exit(void)
 283{
 284        cn_del_callback(&ulog_cn_id);
 285        kfree(prealloced_cn_msg);
 286}
 287
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