miniFSD/OS2KRNL interface

When called from OS2KRNL after being linked into the IFS chain, the 
interface will be as described in previous chapters of this document. Note 
that the FS_ INIT interface for a mini-FSD has an additional parameter, as 
compared to the FS_ INIT interface for an FSD. 

When called from OS2KRNL, before being linked into the IFS chain, the 
interface will be through the MFS_xxxx and MFSH_xxxx entry points. These 
interfaces are described in this chapter. Many of these interfaces 
parallel the interfaces defined for FSDs, while others are unique to the 
mini-FSD. 

The mini-FSD is built as a dynamic link library. Supplied functions are 
exported by making the function names public. Helper functions are 
imported by declaring the helper names external:far. It is required only 
to support reading files and will be called only in protect mode. The 
mini-FSD may NOT make dynamic link system calls at initialization time. 

Due to the special state of the system as it boots, the programming model 
for the mini-FSD during the state 1 time frame is somewhat different than 
the model for stage 2. This difference necessitates 2 different interfaces 
between OS/2 and the mini-FSD. 

During stage 1, all calls to the mini-FSD are to the MFS_xxxx functions. 
Only the MFSH_xxxx helper functions are available. These are the 
interfaces which are addressed in this document. Many of these interfaces 
parallel the interfaces defined for FSDs while others are unique to the 
mini-FSD. 

During stage 2, the mini-FSD is treated as a normal FSD. Calls are made to 
the FS_xxxx functions and all FSH_xxxx helper functions are available. 

During stage 3, the mini-FSD is given a chance to release resources 
(through a call to MFS_TERM) before being terminated. 

Transition from stage 1 to stage 2 is marked by calling the FS_INIT 
function in the mini-FSD. Transition from stage 2 to stage 3 is marked by 
calling FS_ INIT in the FSD. 

Figure 4-3 on page 4-6 shows the functions called during a typical boot 
sequence: 

-------------------------------------------------------------> time
      stage1               stage2               stage3

  MFS_INIT
  MFS_OPEN
  MFS_READ
  MFS_CHGFILEPTR
  MFS_CLOSE

                       FS_INIT
                       FS_MOUNT/ATTACH
                       FS_OPEN
                       FS_READ
                       FS_CHGFILEPTR

                                               MFS_TERM

Figure 4-3. Typical boot sequence   

No files are open at the transition from stage 1 to stage 2. Also, only a 
single file at a time is open during stage 1. Files and volumes are open 
during the transition from stage 2 to stage 3 (the mini-FSD to the FSD). 
The FSD must do whatever is necessary for it to inherit them. The FSD will 
not receive mounts/attaches or opens for volumes and files which were 
mounted/attached and opened by the mini-FSD. Also, multiple files may be 
open simultaneously during stages 2 and 3. 

A special set of helper functions are available to the mini-FSD to support 
an imbedded device driver. This might be required for situations such as 
remote IPL where the boot volume is not readable through DOVOLIO. These 
special helper functions (referred to as imbedded device driver helpers) 
are available during all stages of the mini-FSD's life. Note that the list 
of error return codes for the helper functions is not exhaustive, but 
rather represents the most common errors returned. 

Because the mini-FSD is a new component added to the boot sequence, a new 
interface to OS2LDR is required. 

The name and attributes of the mini-FSD must match EXACTLY the name and 
attributes of the replacement FSD. 

Due to the instability of the system during initialization, any non-zero 
return code indicates an error has been encountered. The actual return 
code may not bake any sense in the context of the function called (for 
example, having ERROR _ACCESS_DENIED returned from a call to MFSH_LOCK 
when in fact an invalid selector was passed to the helper). It is also 
possible for the system to hang or reboot itself as a result of invalid 
parameters being passed to a helper function.