FS_READ

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

Syntax

 FS_READ(psffsi, psffsd, pData, pLen, IOflag)

Parameters

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

Sample

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;

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.