plugins/libvirt/libvirt-plugin.c

   1 /* nbdkit
   2  * Copyright (C) 2013-2018 Red Hat Inc.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions are
   6  * met:
   7  *
   8  * * Redistributions of source code must retain the above copyright
   9  * notice, this list of conditions and the following disclaimer.
  10  *
  11  * * Redistributions in binary form must reproduce the above copyright
  12  * notice, this list of conditions and the following disclaimer in the
  13  * documentation and/or other materials provided with the distribution.
  14  *
  15  * * Neither the name of Red Hat nor the names of its contributors may be
  16  * used to endorse or promote products derived from this software without
  17  * specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
  21  * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
  22  * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
  23  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
  26  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  27  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  28  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  29  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  30  * SUCH DAMAGE.
  31  */
  32
  33 /* libvirt-plugin:
  34  *
  35  * This uses the libvirt virDomainBlockPeek API to access the disks of
  36  * libvirt guests, even remotely.  This only works read-only (since
  37  * libvirt does not have an equivalent write API).
  38  *
  39  * http://libvirt.org/html/libvirt-libvirt.html#virDomainBlockPeek
  40  *
  41  * Note to compile this, ./configure must be able to find libvirt.
  42  * To unconditionally disable this plugin, use ./configure --without-libvirt
  43  */
  44
  45 #include <config.h>
  46
  47 #include <stdio.h>
  48 #include <stdlib.h>
  49 #include <stdint.h>
  50 #include <string.h>
  51 #include <errno.h>
  52
  53 #include <libvirt/libvirt.h>
  54
  55 #include <nbdkit-plugin.h>
  56
  57 /* Configuration. */
  58 static const char *libvirt_uri = NULL;
  59 static const char *domain = NULL;
  60 static const char *disk = NULL;
  61
  62 static int
  63 virt_config (const char *key, const char *value)
  64 {
  65   if (strcmp (key, "connect") == 0) {
  66     libvirt_uri = value;
  67   }
  68   else if (strcmp (key, "domain") == 0) {
  69     domain = value;
  70   }
  71   else if (strcmp (key, "disk") == 0) {
  72     disk = value;
  73   }
  74   else {
  75     nbdkit_error ("unknown parameter '%s'", key);
  76     return -1;
  77   }
  78
  79   return 0;
  80 }
  81
  82 static int
  83 virt_config_complete (void)
  84 {
  85   if (domain == NULL) {
  86     nbdkit_error ("the 'domain' parameter is required");
  87     return -1;
  88   }
  89   if (disk == NULL) {
  90     nbdkit_error ("the 'disk' parameter is required");
  91     return -1;
  92   }
  93   return 0;
  94 }
  95
  96 #define virt_config_help                                        \
  97   "connect=<URI>   (optional) libvirt connection URI\n"         \
  98   "domain=<DOMAIN> (required) libvirt domain name\n"            \
  99   "disk=<DISK>     (required) guest disk name"
 100
 101 /* The per-connection handle. */
 102 struct virt_handle {
 103   virConnectPtr conn;
 104   virDomainPtr dom;
 105   uint64_t exportsize;
 106 };
 107
 108 /* Create the per-connection handle. */
 109 static void *
 110 virt_open (int readonly)
 111 {
 112   struct virt_handle *h;
 113   virDomainBlockInfo info;
 114
 115   h = malloc (sizeof *h);
 116   if (h == NULL) {
 117     nbdkit_error ("malloc: %m");
 118     return NULL;
 119   }
 120
 121   /* Connect to libvirt. */
 122   h->conn = virConnectOpen (libvirt_uri);
 123   if (!h->conn) {
 124     nbdkit_error ("virConnectOpen failed, see earlier error messages");
 125     goto err1;
 126   }
 127
 128   /* Open the domain. */
 129   h->dom = virDomainLookupByName (h->conn, domain);
 130   if (!h->dom) {
 131     nbdkit_error ("virDomainLookupByName: "
 132                   "cannot open domain '%s'", domain);
 133     goto err2;
 134   }
 135
 136   if (virDomainGetBlockInfo (h->dom, disk, &info, 0) == -1) {
 137     nbdkit_error ("virDomainGetBlockInfo: "
 138                   "cannot read information about disk '%s' from domain '%s'",
 139                   disk, domain);
 140     goto err3;
 141   }
 142   h->exportsize = info.physical;
 143
 144   return h;
 145
 146 err3:
 147   virDomainFree (h->dom);
 148 err2:
 149   virConnectClose (h->conn);
 150 err1:
 151   free (h);
 152   return NULL;
 153 }
 154
 155 /* Free up the per-connection handle. */
 156 static void
 157 virt_close (void *handle)
 158 {
 159   struct virt_handle *h = handle;
 160
 161   virDomainFree (h->dom);
 162   virConnectClose (h->conn);
 163   free (h);
 164 }
 165
 166 #define THREAD_MODEL NBDKIT_THREAD_MODEL_SERIALIZE_REQUESTS
 167
 168 /* Get the file size. */
 169 static int64_t
 170 virt_get_size (void *handle)
 171 {
 172   struct virt_handle *h = handle;
 173
 174   return h->exportsize;
 175 }
 176
 177 /* Read data from the file. */
 178 static int
 179 virt_pread (void *handle, void *buf, uint32_t count, uint64_t offset)
 180 {
 181   struct virt_handle *h = handle;
 182   uint32_t c;
 183
 184   while (count > 0) {
 185     /* Limit requests to 1MB, which was the limit in 0.9.13 (it has since
 186      * been raised).
 187      */
 188     c = count;
 189     if (c > 1024*1024)
 190       c = 1024*1024;
 191
 192     if (virDomainBlockPeek (h->dom, disk, offset, c, buf, 0) == -1) {
 193       nbdkit_error ("virDomainBlockPeek: cannot read block from disk '%s'",
 194                     disk);
 195       errno = EIO;
 196       return -1;
 197     }
 198
 199     buf += c;
 200     count -= c;
 201     offset += c;
 202   }
 203
 204   return 0;
 205 }
 206
 207 static struct nbdkit_plugin plugin = {
 208   .name              = "libvirt",
 209   .longname          = "nbdkit libvirt plugin",
 210   .version           = PACKAGE_VERSION,
 211   .config            = virt_config,
 212   .config_complete   = virt_config_complete,
 213   .config_help       = virt_config_help,
 214   .open              = virt_open,
 215   .close             = virt_close,
 216   .get_size          = virt_get_size,
 217   .pread             = virt_pread,
 218 };
 219
 220 NBDKIT_REGISTER_PLUGIN(plugin)