Boot-time loadable drivers

What drivers should be BTLD

Drivers should be boot-time loadable if they are not part of the standard installation kernel but they are required to install the operating system. These include:

Any driver for a disk device (SCSI or non-SCSI, and including SCSI host adapters as well as the SCSI peripheral driver), so it can be used for the primary hard disk on which the root filesystem is loaded.
Any driver for a tape or CD-ROM device (SCSI or non-SCSI, and including SCSI host adapters as well as the SCSI peripheral driver) that could be used as distribution media for the operating system.
Any driver that will be included in the SCO Advanced Hardware Supplement (AHS) and is not a Network MDI, Advanced Graphic Adapter, or Multiprocessing platform (GPI) driver.

In SCO OpenServer 5 Release 5 onwards, a BTLD can be used to replace an existing driver if the ahslink command is used to load the driver rather than the link(HW) command. In a future release, this functionality of ahslink will be merged into link.

Note the following restrictions on BTLDs:

STREAMS drivers cannot be boot-time loadable.
Pseudo-drivers, STREAMS modules, and other software drivers that are not accessed through the cdevsw and/or bdevsw tables cannot be boot-time loadable.
A replacement driver's Master file entry must match the existing Master file entry exactly or the BTLD driver will be installed as a new driver rather than replacing the existing driver.
Some driver characteristics defined in the mdevice(F) file cannot be used for BTLDs. See the ``Limitations'' section of the btld(F) manual page for a detailed list.
``Guidelines for writing BTLDs'' contains a list of restrictions for coding a BTLD.