
         Chapter 26. Virtual Tape API
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Chapter 26. Virtual Tape API


Stefan G. Weichinger

XML-conversion
AMANDA Core Team
<sgw@amanda.org>

Note

Refer to http://www.amanda.org/docs/vtape-api.html for the current version of
this document.
The upper level AMANDA code (including some of the other tape_xxx routines)
calls the following routines which implement a virtual tape table:

* int tape_access(filename, mode) Acts like access(2) on possibly virtual
  devices
* int tape_open(filename, mode) Acts like open(2) on possibly virtual devices
* int tape_stat(filename, buf) Acts like stat(2) on possibly virtual devices
* int tapefd_close(tapefd) Acts like close(2) on possibly virtual devices
* int tapefd_fsf(tapefd, count) Forward skips the (possibly virtual) device.
* int tapefd_read(tapefd, buffer, count) Reads a block from the (possibly
  virtual) device.
* int tapefd_rewind(tapefd) Reads a block from a (possibly virtual) device.
* void tapefd_resetofs(tapefd) Uses lseek() tricks to reset the write/read
  offset counter on a virtual tape device.
* int tapefd_unload(tapefd) Unloads the media from a (possibly virtual) device.
* int tapefd_status(tapefd) pr- ints status of the (possibly virtual) device to
  standard output.
* int tapefd_weof(tapefd, count) writes a filemark/moves to the next file on a
  device for writing.
* int tapefd_write(tapefd, buffer, count) writes a block of data to a (possibly
  virtual) device.

For a tape type xxx, the following routines must be provided, and entered -
into the table "vtable" in tape-src/tapeio.c:

* int xxx_tape_access(filename, mode)
* int xxx_tape_open(filename, mode)
* int xxx_tape_stat(filename, buf)
* int xxx_tapefd_close(xxx_tapefd)
* int xxx_tapefd_fsf(xxx_tapefd, count)
* int xxx_tapefd_read(xxx_tapefd, buffer, count)
* int xxx_tapefd_rewind(xxx_tapefd)
* void xxx_tapefd_resetofs(xxx_tapefd)
* int xxx_tapefd_unload(xxx_tapefd)
* int xxx_tapefd_status(xxx_tapefd)
* int xxx_tapefd_weof(xxx_tapefd, count)
* int xxx_tapefd_write(xxx_tapefd, buffer, count)

Along with a prefix string which will identify the type. The initial vtape
layer has two types "plain" and "rait" (Redundant Array of Inexpensive Tapes)
but we hope to add a "rmt" (remote tape client), and possibly "dvd" types soon.
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