filters/scan/bgthread.c

   1 /* nbdkit
   2  * Copyright Red Hat
   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 #include <config.h>
  34
  35 #include <stdio.h>
  36 #include <stdlib.h>
  37 #include <stdint.h>
  38 #include <pthread.h>
  39
  40 #include <nbdkit-filter.h>
  41
  42 #include "scan.h"
  43
  44 #include "cleanup.h"
  45 #include "minmax.h"
  46
  47 static pthread_mutex_t clock_lock;
  48 static uint64_t clock_ = 0;
  49
  50 static void
  51 adjust_clock (uint64_t offset)
  52 {
  53   ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&clock_lock);
  54   if (clock_ < offset)
  55     clock_ = offset;
  56 }
  57
  58 static void
  59 reset_clock (uint64_t offset)
  60 {
  61   ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&clock_lock);
  62   clock_ = 0;
  63 }
  64
  65 static uint64_t
  66 get_starting_offset (void)
  67 {
  68   ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&clock_lock);
  69   return scan_clock ? clock_ : 0;
  70 }
  71
  72 void *
  73 scan_thread (void *vp)
  74 {
  75   struct bgthread_ctrl *ctrl = vp;
  76   uint64_t offset, size;
  77   int64_t r;
  78
  79   assert (ctrl->next != NULL);
  80
  81   /* Get the size of the underlying plugin.  Exit the thread on error
  82    * because there's not much we can do without knowing the size.
  83    */
  84   r = ctrl->next->get_size (ctrl->next);
  85   if (r == -1)
  86     return NULL;
  87   size = r;
  88
  89   /* Start scanning. */
  90  start:
  91   for (offset = get_starting_offset (); offset < size; offset += scan_size) {
  92     uint64_t n;
  93
  94     /* Execute any commands in the queue. */
  95     {
  96       ACQUIRE_LOCK_FOR_CURRENT_SCOPE (&ctrl->lock);
  97       struct command cmd;
  98
  99       while (ctrl->cmds.len) {
 100         cmd = ctrl->cmds.ptr[0];
 101         command_queue_remove (&ctrl->cmds, 0);
 102
 103         switch (cmd.type) {
 104         case CMD_QUIT:
 105           nbdkit_debug ("scan: exiting background thread on connection close");
 106           return NULL;
 107
 108         case CMD_NOTIFY_PREAD:
 109           if (offset < cmd.offset)
 110             offset = cmd.offset;
 111         }
 112       }
 113     }
 114
 115     adjust_clock (offset);
 116
 117     if (offset < size) {
 118       /* Issue the next prefetch. */
 119       n = MIN (scan_size, size - offset);
 120       ctrl->next->cache (ctrl->next, n, offset, 0, NULL);
 121     }
 122   }
 123
 124   if (scan_forever) {
 125     reset_clock (offset);
 126     goto start;
 127   }
 128
 129   nbdkit_debug ("scan: finished scanning the plugin");
 130   return NULL;
 131 }