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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 
17 
18 static 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
32 static struct cn_msg *prealloced_cn_msg;
33 static struct dm_ulog_request *prealloced_ulog_tfr;
34 
35 static struct cb_id ulog_cn_id = {
36  .idx = CN_IDX_DM,
38 };
39 
40 static DEFINE_MUTEX(dm_ulog_lock);
41 
42 struct receiving_pkg {
43  struct list_head list;
45 
47 
48  int error;
49  size_t *data_size;
50  char *data;
51 };
52 
53 static DEFINE_SPINLOCK(receiving_list_lock);
54 static struct list_head receiving_list;
55 
56 static 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  */
82 static 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  */
133 static 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 
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;
192 resend:
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);
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 
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 
255 out:
256  return r;
257 }
258 
260 {
261  int r;
262  void *prealloced;
263 
264  INIT_LIST_HEAD(&receiving_list);
265 
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 
283 {
284  cn_del_callback(&ulog_cn_id);
285  kfree(prealloced_cn_msg);
286 }