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Writing Device Drivers
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Character Device Autoconfiguration

The attach(9E) routine should perform the common initialization tasks that all devices require, such as:

  • Allocating per-instance state structures

  • Registering device interrupts

  • Mapping the device's registers

  • Initializing mutex variables and condition variables

  • Creating power-manageable components

  • Creating minor nodes

See attach() Entry Point for code examples of these tasks.

Character device drivers create minor nodes of type S_IFCHR. A minor node of S_IFCHR causes a character special file that represents the node to eventually appear in the /devices hierarchy.

The following example shows a typical attach(9E) routine for character drivers. Properties that are associated with the device are commonly declared in an attach() routine. This example uses a predefined Size property. Size is the equivalent of the Nblocks property for getting the size of partition in a block device. If, for example, you are doing character I/O on a disk device, you might use Size to get the size of a partition. Since Size is a 64-bit property, you must use a 64-bit property interface. In this case, you use ddi_prop_update_int64(9F). See Device Properties for more information about properties.

Example 15-1 Character Driver attach() Routine
static int
xxattach(dev_info_t *dip, ddi_attach_cmd_t cmd)
  int instance = ddi_get_instance(dip);
  switch (cmd) {
  case DDI_ATTACH:
       * Allocate a state structure and initialize it.
       * Map the device's registers.
       * Add the device driver's interrupt handler(s).
       * Initialize any mutexes and condition variables.
       * Create power manageable components.
       * Create the device's minor node. Note that the node_type
       * argument is set to DDI_NT_TAPE.
       if (ddi_create_minor_node(dip, minor_name, S_IFCHR,
           instance, DDI_NT_TAPE, 0) == DDI_FAILURE)
           /* Free resources allocated so far. */
           /* Remove any previously allocated minor nodes. */
           ddi_remove_minor_node(dip, NULL);
           return (DDI_FAILURE);
       * Create driver properties like "Size." Use "Size"
       * instead of "size" to ensure the property works
       * for large bytecounts.
       xsp->Size = size_of_device_in_bytes;
       maj_number = ddi_driver_major(dip);
       if (ddi_prop_update_int64(makedevice(maj_number, instance),
           dip, "Size", xsp->Size) != DDI_PROP_SUCCESS) {
           cmn_err(CE_CONT, "%s: cannot create Size property\n",
               /* Free resources allocated so far. */
           return (DDI_FAILURE);
      /* ... */
      return (DDI_SUCCESS);
      /* See the "Power Management" chapter in this book. */
      return (DDI_FAILURE);
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  Published under the terms fo the Public Documentation License Version 1.01. Design by Interspire