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devsw_add(9r)


NAME

  devsw_add - General: Registers driver entry points and reserves a major
  number


SYNOPSIS

  #include <sys/conf.h>


  int devsw_add(
	  char *driver_name,
	  int driver_reg_instance,
	  int major_number,
	  struct dsent *dsent_ptr );


ARGUMENTS

  driver_name
      Specifies a null-terminated string that represents the name of the
      device driver whose entry points you want to register and for which you
      want to reserve an associated major number.  The driver name must be at
      least two characters in length not to exceed DEVSW_NAME_LEN characters,
      including the null terminator. This name is a string that matches the
      string you specified for the entry_name item in the /etc/sysconfigtab
      database. Typically, third-party driver writers specify the driver name
      (followed by a colon) in the sysconfigtab file fragment, which gets
      appended to the /etc/sysconfigtab database during the driver product
      installation.

  driver_reg_instance
      Specifies an integer that represents a specific reservation instance
      for this driver. This argument allows a driver to uniquely identify
      multiple major numbers for the driver.

  major_number
      Specifies the major number you want to reserve for the driver in the
      dsent table. You can pass a specific major number or the value -1, in
      which case the devsw_add interface chooses the major number.

  dsent_ptr
      Specifies a pointer to the device switch structure that contains
      pointers to the device driver's entry points for the system service's
      I/O requests and other information.


DESCRIPTION

  The devsw_add interface registers a device driver's I/O services interfaces
  in and reserves a major number from a free slot in the dsent table. Tru64
  UNIX reserves this major number across boots. The devsw_add interface
  performs appropriate checks on the values passed to the driver_name,
  major_number, and dsent_ptr arguments.

  You can request that the devsw_add interface reserve a specific major
  number from a slot in the dsent table by passing a specific number to the
  major_number argument.  If you pass a specific major number, the devsw_add
  interface determines if a major number has already been assigned to the
  device driver.  If this major number was already assigned to the device
  driver, the devsw_add interface simply registers the driver's I/O services
  interfaces in the dsent table and returns the major number as the reserved
  number. Passing the value -1 to the major_number argument causes the
  devsw_add interface to reserve a previously reserved major number or the
  next available major number from a slot in the dsent table.

  If the major number you request or if the major number that was previously
  reserved is too large for the current size of the device switch table,
  devsw_add returns an error value of -1.

  You can make subsequent calls to devsw_add to modify the device switch
  entry in the device switch table.


NOTES

  The dsent data structure contains entry points for the block and character
  I/O services interfaces associated with a specific device driver. This data
  structure also contains other information such as whether the driver is
  implemented as a symmetric multiprocessing (SMP) driver.

  The devsw_add interface is provided for registering these block and
  character I/O services interfaces and reserving an associated major number.

  A device driver writer registers the driver's I/O services interfaces by
  declaring an instance of the dsent structure in the driver and setting the
  appropriate members to the names of the driver's I/O services interfaces.
  You must specify an interface name for each member of this structure. If
  the driver does not implement a specific interface, there are typically two
  interfaces you can specify:

    ·  The nodev interface

       You specify nodev when it is an error for the interface to be called.
       To indicate the error, nodev returns ENODEV.

    ·  The nulldev interface

       You specify nulldev when it is not an error for the interface to be
       called, but the driver has no need to implement the interface.  The
       nulldev interface returns the value zero (0) and performs no tasks.
       This value indicates a success status.


EXAMPLE

  See Writing Device Drivers: Tutorial for a code example of the devsw_add
  interface.


RETURN VALUES

  Upon successful completion, the devsw_add interface returns the reserved
  major number. Otherwise, on an error, the devsw_add interface returns the
  value -1. The following list describes possible error conditions:

    ·  The devsw_add interface is not available to be called at this point in
       the driver.

    ·  The name you passed to the driver_name argument is not a valid name.

    ·  The requested or reserved major number is too large for the current
       table.

    ·  The requested major number is not available.

    ·  The requested major number is not the same as the reserved major
       number.

    ·  The pointer passed to the dsent_ptr argument is not valid.


SEE ALSO

  Kernel Interfaces: devsw_del(9r), devsw_get(9r)

  Data Structures: dsent(9s)

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