why CURRENT->sector is zero??

[mohanlal jangir]

I downloaded sbull.c (for LDD 2nd Edition) from 
http://examples.oreilly.com/linuxdrive/. After compiling and inserting 
(registering as block device), I tried to mount different file systems 
(Although there is no valid file system there; my goal is to observe value 
of req->sector in sbull_transfer function). The observations are as follows:
File System  req->sector
msdos          0
vfat              0
ext2             2
ext3             2
iso9000       72

I don't know about other file systems, but I believe the value of 
req->sector for msdos/vfat is wrong. Because when I mount a CF card having 
FAT file system on my Linux box (using USB mass storage driver), the first 
read request contains sector 0x20.
Does someone have any clue, why sbull gets this value as 0 rather then 0x20? 
Basically this means why CURRENT->sector is 0?
I am working on 2.4.18; a little old :(

Regards
Mohanlal 

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