Root/drivers/md/dm-log-userspace-transfer.c

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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