plugins/golang/examples/disk/disk.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         "io/ioutil"
  38         "libguestfs.org/nbdkit"
  39         "os"
  40         "strconv"
  41         "unsafe"
  42 )
  43
  44 var pluginName = "disk"
  45
  46 // The plugin global struct.
  47 type DiskPlugin struct {
  48         nbdkit.Plugin
  49 }
  50
  51 // The per-client struct.
  52 type DiskConnection struct {
  53         nbdkit.Connection
  54         fd *os.File // Per-client temporary disk.
  55 }
  56
  57 var size uint64
  58 var size_set = false
  59
  60 // Parse the size parameter on the command line.
  61 func (p *DiskPlugin) Config(key string, value string) error {
  62         if key == "size" {
  63                 var err error
  64                 size, err = strconv.ParseUint(value, 0, 64)
  65                 if err != nil {
  66                         return err
  67                 }
  68                 size_set = true
  69                 return nil
  70         } else {
  71                 return nbdkit.PluginError{Errmsg: "unknown parameter"}
  72         }
  73 }
  74
  75 // Make sure the user specified the size parameter.
  76 func (p *DiskPlugin) ConfigComplete() error {
  77         if !size_set {
  78                 return nbdkit.PluginError{Errmsg: "size parameter is required"}
  79         }
  80         return nil
  81 }
  82
  83 func (p *DiskPlugin) Open(readonly bool) (nbdkit.ConnectionInterface, error) {
  84         // Open a temporary file.
  85         fd, err := ioutil.TempFile("/var/tmp", "nbdkitdisk")
  86         if err != nil {
  87                 return nil, err
  88         }
  89         os.Remove(fd.Name())
  90
  91         // Truncate it to the right size.
  92         err = fd.Truncate(int64(size))
  93         if err != nil {
  94                 return nil, err
  95         }
  96
  97         // Store the file descriptor of the temporary file in the
  98         // Connection struct.
  99         return &DiskConnection{fd: fd}, nil
 100 }
 101
 102 func (c *DiskConnection) Close() {
 103         c.fd.Close()
 104 }
 105
 106 // Return the size of the disk.  We could just return the global
 107 // "size" here, but make the example more interesting.
 108 func (c *DiskConnection) GetSize() (uint64, error) {
 109         info, err := c.fd.Stat()
 110         if err != nil {
 111                 return 0, err
 112         }
 113         return uint64(info.Size()), nil
 114 }
 115
 116 // Multi-conn is NOT safe because each client sees a different disk.
 117 func (c *DiskConnection) CanMultiConn() (bool, error) {
 118         return false, nil
 119 }
 120
 121 func (c *DiskConnection) PRead(buf []byte, offset uint64,
 122         flags uint32) error {
 123         n, err := c.fd.ReadAt(buf, int64(offset))
 124         if err != nil {
 125                 return err
 126         }
 127         // NBD requests must always read/write the whole requested
 128         // amount, or else fail.  Actually we should loop here (XXX).
 129         if n != len(buf) {
 130                 return nbdkit.PluginError{Errmsg: "short read"}
 131         }
 132         return nil
 133 }
 134
 135 // Note that CanWrite() is required in golang plugins that implement
 136 // PWrite(), otherwise PWrite() will never be called.
 137 func (c *DiskConnection) CanWrite() (bool, error) {
 138         return true, nil
 139 }
 140
 141 func (c *DiskConnection) PWrite(buf []byte, offset uint64,
 142         flags uint32) error {
 143         n, err := c.fd.WriteAt(buf, int64(offset))
 144         if err != nil {
 145                 return err
 146         }
 147         // NBD requests must always read/write the whole requested
 148         // amount, or else fail.  Actually we should loop here (XXX).
 149         if n != len(buf) {
 150                 return nbdkit.PluginError{Errmsg: "short write"}
 151         }
 152         return nil
 153 }
 154
 155 // Note that CanFlush() is required in golang plugins that implement
 156 // Flush(), otherwise Flush() will never be called.
 157 func (c *DiskConnection) CanFlush() (bool, error) {
 158         return true, nil
 159 }
 160
 161 // This is only an example, but if this was a real plugin, because
 162 // these disks are transient and deleted when the client exits, it
 163 // would make no sense to implement a Flush() callback.
 164 func (c *DiskConnection) Flush(flags uint32) error {
 165         return c.fd.Sync()
 166 }
 167
 168 //----------------------------------------------------------------------
 169 //
 170 // The boilerplate below this line is required by all golang plugins,
 171 // as well as importing "C" and "unsafe" modules at the top of the
 172 // file.
 173
 174 //export plugin_init
 175 func plugin_init() unsafe.Pointer {
 176         // If your plugin needs to do any initialization, you can
 177         // either put it here or implement a Load() method.
 178         // ...
 179
 180         // Then you must call the following function.
 181         return nbdkit.PluginInitialize(pluginName, &DiskPlugin{})
 182 }
 183
 184 // This is never(?) called, but must exist.
 185 func main() {}