plugins/golang/examples/ramdisk/ramdisk.go

   1 /* Example plugin.
   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 package main
  34
  35 import (
  36         "C"
  37         "libguestfs.org/nbdkit"
  38         "strconv"
  39         "unsafe"
  40 )
  41
  42 var pluginName = "ramdisk"
  43
  44 type RAMDiskPlugin struct {
  45         nbdkit.Plugin
  46 }
  47
  48 type RAMDiskConnection struct {
  49         nbdkit.Connection
  50 }
  51
  52 var size uint64
  53 var size_set = false
  54 var disk []byte
  55
  56 func (p *RAMDiskPlugin) Config(key string, value string) error {
  57         if key == "size" {
  58                 var err error
  59                 size, err = strconv.ParseUint(value, 0, 64)
  60                 if err != nil {
  61                         return err
  62                 }
  63                 size_set = true
  64                 return nil
  65         } else {
  66                 return nbdkit.PluginError{Errmsg: "unknown parameter"}
  67         }
  68 }
  69
  70 func (p *RAMDiskPlugin) ConfigComplete() error {
  71         if !size_set {
  72                 return nbdkit.PluginError{Errmsg: "size parameter is required"}
  73         }
  74         return nil
  75 }
  76
  77 func (p *RAMDiskPlugin) GetReady() error {
  78         // Allocate the RAM disk.
  79         disk = make([]byte, size)
  80         return nil
  81 }
  82
  83 func (p *RAMDiskPlugin) Open(readonly bool) (nbdkit.ConnectionInterface, error) {
  84         return &RAMDiskConnection{}, nil
  85 }
  86
  87 func (c *RAMDiskConnection) GetSize() (uint64, error) {
  88         return size, nil
  89 }
  90
  91 // Clients are allowed to make multiple connections safely.
  92 func (c *RAMDiskConnection) CanMultiConn() (bool, error) {
  93         return true, nil
  94 }
  95
  96 func (c *RAMDiskConnection) PRead(buf []byte, offset uint64,
  97         flags uint32) error {
  98         copy(buf, disk[offset:int(offset)+len(buf)])
  99         return nil
 100 }
 101
 102 // Note that CanWrite is required in golang plugins, otherwise PWrite
 103 // will never be called.
 104 func (c *RAMDiskConnection) CanWrite() (bool, error) {
 105         return true, nil
 106 }
 107
 108 func (c *RAMDiskConnection) PWrite(buf []byte, offset uint64,
 109         flags uint32) error {
 110         copy(disk[offset:int(offset)+len(buf)], buf)
 111         return nil
 112 }
 113
 114 //----------------------------------------------------------------------
 115 //
 116 // The boilerplate below this line is required by all golang plugins,
 117 // as well as importing "C" and "unsafe" modules at the top of the
 118 // file.
 119
 120 //export plugin_init
 121 func plugin_init() unsafe.Pointer {
 122         // If your plugin needs to do any initialization, you can
 123         // either put it here or implement a Load() method.
 124         // ...
 125
 126         // Then you must call the following function.
 127         return nbdkit.PluginInitialize(pluginName, &RAMDiskPlugin{})
 128 }
 129
 130 // This is never(?) called, but must exist.
 131 func main() {}