FS_READ - Read from a File

Purpose   

Read the specified number of bytes from a file to a buffer location. 

Calling Sequence   

int far pascal FS_READ(psffsi, psffsd, pData, pLen, IOflag)

struct sffsi far * psffsi;
struct sffsd far * psffsd;
char far * pData;
unsigned short far * pLen;
unsigned short IOflag;

Where   

psffsi is a pointer to the file-system-independent portion of an open file 
instance. 

sfi_position is the location within the file where the data is to be read 
from. The FSD should update the sfi_position field. 

psffsd is a pointer to the file-system-dependent portion of an open file 
instance. 

pData is the address of the application data area. 

Addressing of this data area has not been validated by the kernel (see 
FSH_ PROBEBUF). 

pLen is a pointer to the length of the application data area. 

On input, this is the number of bytes to be read. On output, this is the 
number of bytes successfully read. If the application data area is smaller 
than the length, no transfer is to take place. The FSD will not be called 
for zero length reads. The FSD does not need to verify this pointer. 

IOflag indicates information about the operation on the handle. 

IOflag == 0x0010 indicates write-through 
IOflag == 0x0020 indicates no-cache 
  

Remarks   

If read is successful and is a file, the FSD should set ST_SREAD and 
ST_PREAD to make the kernel time stamp the last modification time in the 
SFT. 

Of the information passed in IOflag, the write-through bit is a mandatory 
bit in that any data written to the block device must be put out on the 
medium before the device driver returns. The no-cache bit, on the other 
hand, is an advisory bit that says whether the data being transferred is 
worth caching or not.