The following figure represents the major stages of the OS/2 Version 2.0 BIFS boot procedure.

ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ time
    POST     BlackBox    OS2LDR     stage1     stage2      stage3
             (Micro                 OS2KRNL
                 FSD)

Figure 4-2. OS/2 Version 2.0 BIFS boot procedure

The major difference between this boot procedure and the FAT boot procedure is that there is no assumption of booting off of disk. OS/2 Version 2.0 does not define what should happen between when the POST code is run and when the OS2LDR program gains control.

When OS2LDR receives control, it must be passed information about the current state of memory and pointers to the Open, Read, Close, and Terminate entry points of the micro-FSD. Included in the memory map information is the positions of the micro-FSD, mini-FSD, RIPL data, and the OS2LDR file itself.

Note: This interface is defined in a next section of this chapter.

As with the FAT boot procedure, the OS/2 loader relocates itself to the top of low memory, and with the help of the micro-FSD, scans the root directory for the OS2KRNL file. After reading OS2KRNL into memory and applying the required fixups, control is transferred to the kernel.

When OS2KRNL receives control, it goes through the same initialization as before (stage 1) with a couple of exceptions. The module loader is called to load the mini-FSD from its memory image stored by OS2LDR in high memory to its final location at the top of low memory. Also, the mini-FSD is called to read the base device drivers (one at a time) through the stage 1 interfaces.

Before any of the dynalinks are loaded, the mini-FSD will be linked into the IFS chain (it will be the only link in the chain) and asked to initialize through FS_INIT. The FS_INIT call marks the transition from stage 1 to stage 2.

The dynalinks are then loaded using the stage 2 interfaces, followed by the device drivers and FSDs.

The mini-FSD is required to support only a small number of the FSD system interfaces (the FS_xxxx calls). Therefore, the first FSD loaded must be the replacement for the mini-FSD.

After the replacement FSD has been loaded, it is called at FS_INIT to initialize itself and take whatever action it needs to effect a smooth transition from the mini-FSD to the FSD. It then replaces the mini-FSD in the IFS chain, as well as in any kernel data structures which keep a handle to the FSD (for example, the SFT, VPB). This replacement marks the transition from stage 2 to stage 3.

From this point on, the system continues normally.