filters/nozero/nozero.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 <string.h>
  39 #include <stdbool.h>
  40 #include <assert.h>
  41 #include <errno.h>
  42
  43 #include <nbdkit-filter.h>
  44
  45 #include "minmax.h"
  46
  47 /* IGNORE is defined as a macro in Windows headers files ... */
  48 #ifdef IGNORE
  49 #undef IGNORE
  50 #endif
  51
  52 static enum ZeroMode {
  53   NONE,
  54   EMULATE,
  55   NOTRIM,
  56   PLUGIN,
  57 } zeromode;
  58
  59 static enum FastZeroMode {
  60   DEFAULT,
  61   SLOW,
  62   IGNORE,
  63   NOFAST,
  64 } fastzeromode;
  65
  66 static int
  67 nozero_config (nbdkit_next_config *next, nbdkit_backend *nxdata,
  68                const char *key, const char *value)
  69 {
  70   if (strcmp (key, "zeromode") == 0) {
  71     if (strcmp (value, "emulate") == 0)
  72       zeromode = EMULATE;
  73     else if (strcmp (value, "notrim") == 0)
  74       zeromode = NOTRIM;
  75     else if (strcmp (value, "plugin") == 0)
  76       zeromode = PLUGIN;
  77     else if (strcmp (value, "none") != 0) {
  78       nbdkit_error ("unknown zeromode '%s'", value);
  79       return -1;
  80     }
  81     return 0;
  82   }
  83
  84   if (strcmp (key, "fastzeromode") == 0) {
  85     if (strcmp (value, "none") == 0)
  86       fastzeromode = NOFAST;
  87     else if (strcmp (value, "ignore") == 0)
  88       fastzeromode = IGNORE;
  89     else if (strcmp (value, "slow") == 0)
  90       fastzeromode = SLOW;
  91     else if (strcmp (value, "default") != 0) {
  92       nbdkit_error ("unknown fastzeromode '%s'", value);
  93       return -1;
  94     }
  95     return 0;
  96   }
  97
  98   return next (nxdata, key, value);
  99 }
 100
 101 #define nozero_config_help \
 102   "zeromode=<MODE>      One of 'none' (default), 'emulate', 'notrim', 'plugin'.\n" \
 103   "fastzeromode=<MODE>  One of 'default', 'none', 'slow', 'ignore'.\n"
 104
 105 /* Check that desired mode is supported by plugin. */
 106 static int
 107 nozero_prepare (nbdkit_next *next, void *handle,
 108                 int readonly)
 109 {
 110   int r;
 111
 112   /* If we are opened readonly, this filter has no impact */
 113   if (readonly)
 114     return 0;
 115
 116   if (zeromode == NOTRIM || zeromode == PLUGIN) {
 117     r = next->can_zero (next);
 118     if (r == -1)
 119       return -1;
 120     if (!r) {
 121       nbdkit_error ("zeromode '%s' requires plugin zero support",
 122                     zeromode == NOTRIM ? "notrim" : "plugin");
 123       return -1;
 124     }
 125   }
 126   return 0;
 127 }
 128
 129 /* Advertise desired WRITE_ZEROES mode. */
 130 static int
 131 nozero_can_zero (nbdkit_next *next, void *handle)
 132 {
 133   switch (zeromode) {
 134   case NONE:
 135     return NBDKIT_ZERO_NONE;
 136   case EMULATE:
 137     return NBDKIT_ZERO_EMULATE;
 138   default:
 139     return next->can_zero (next);
 140   }
 141 }
 142
 143 /* Advertise desired FAST_ZERO mode. */
 144 static int
 145 nozero_can_fast_zero (nbdkit_next *next,
 146                       void *handle)
 147 {
 148   if (zeromode == NONE)
 149     return 0;
 150   if (zeromode != EMULATE && fastzeromode == DEFAULT)
 151     return next->can_fast_zero (next);
 152   return fastzeromode != NOFAST;
 153 }
 154
 155 static int
 156 nozero_zero (nbdkit_next *next,
 157              void *handle, uint32_t count, uint64_t offs, uint32_t flags,
 158              int *err)
 159 {
 160   assert (zeromode != NONE && zeromode != EMULATE);
 161   if (flags & NBDKIT_FLAG_FAST_ZERO) {
 162     assert (fastzeromode != NOFAST);
 163     if (fastzeromode == SLOW) {
 164       *err = ENOTSUP;
 165       return -1;
 166     }
 167     if (fastzeromode == IGNORE)
 168       flags &= ~NBDKIT_FLAG_FAST_ZERO;
 169   }
 170
 171   if (zeromode == NOTRIM)
 172     flags &= ~NBDKIT_FLAG_MAY_TRIM;
 173
 174   return next->zero (next, count, offs, flags, err);
 175 }
 176
 177 static struct nbdkit_filter filter = {
 178   .name              = "nozero",
 179   .longname          = "nbdkit nozero filter",
 180   .config            = nozero_config,
 181   .config_help       = nozero_config_help,
 182   .prepare           = nozero_prepare,
 183   .can_zero          = nozero_can_zero,
 184   .can_fast_zero     = nozero_can_fast_zero,
 185   .zero              = nozero_zero,
 186 };
 187
 188 NBDKIT_REGISTER_FILTER (filter)