SCO OpenServer

physio(D3oddi)

physio, physck -- direct (raw) I/O for block drivers

Synopsis

#include <sys/buf.h>

int physck(daddr_t nblocks, int rwflags);

void physio(int (strategy) (struct buf ), struct buf bp,
	    dev_t dev, int rwflags);

Description

The physio function supports raw (direct) I/O for block devices. It validates the request, locks the relevant pages of the process in core, and examines the driver's attributes to determine how to handle the I/O request. It then builds an appropriate number of buffer headers and passes these to the driver with calls to the driver's strategy(D2oddi) routine.

physck ensures that a requested raw I/O request can be serviced by the device being read from or written to.

Arguments

nblocks

maximum number of 512-byte blocks on the device, or in the disk partition. The number of blocks is converted to bytes to find the size limit and then compared with u.u_offset.

strategy

Address of the driver's strategy(D2oddi) routine.

bp

Retained for backward compatibility; should be set to NULL.

dev

device number (includes both major and minor device numbers).

rwflags

defines the I/O operation. Valid values are:

B_READ: read operation
B_WRITE: write operation
B_BDEV: If set, device attributes are determined through the getbattr( ) function; if not set, these attributes are determined through the getcattr( ) function.
B_NOSG: no scatter/gather

Implicit arguments:

u.u_base: start address for transfer
u.u_count: count for transfer
u.u_offset: offset on device for transfer (see u.u_fmode description)
u.u_segflg: 0 indicates user data, 1 indicates system data
u.u_fmode: if FBMODE is set, u.u_offset is in units of 512-byte sectors; otherwise, in units of bytes
u.u_error: checked to see if an error has been recorded

The u.u_base, u.u_count, and u.u_offset values must be set up prior to the physio call, and must point to the appropriate user-data area.

Return values

physck returns 0 (zero) on an error; 1 if successful: Note the following side effects:

If u.u_offset is greater than the size limit, and rwflag is set to B_WRITE, then u.u_error is set to ENXIO and 0 (zero) is returned.
If u.u_offset is greater than or equal to the limit, and rwflag is B_READ, then 0 (zero) is returned and no error is set.
If u.u_offset plus u.u_count is greater than the limit, then u.u_count is reduced by the number of bytes that it differs from the limit and the test is completed.

physio does not return a value. Various globals are updated:

u.u_base: incremented by amount of data transferred
u.u_count: decremented by amount of data transferred
u.u_offset: incremented by amount of data transferred
u.u_error: set to an appropriate value if error occurred
c_sysinfo->phread: incremented if this was a read operation
c_sysinfo->phwrite: incremented if this was a write operation

Usage

The following example illustrates a typical call to physio:

   physio(mystrategy, (struct buf *) NULL, dev, B_READ);

physio( ) handles various device characteristics as defined in the mdevice(F) file:

If the device allows scatter/gather operations (option g in the mdevice file) and the required data transfer is most efficiently performed by scatter/gather, physio( ) prepares the appropriate scatter/gather lists for the driver.
If the device cannot handle physical addresses beyond 16MB (option d is not set in the mdevice file), then physio( ) uses copy buffers below the 16MB limit as required.
physio( ) is aware of q and u options in the mdevice file and uses them to determine the block size prior to checking if partial block accesses are required. Unless the T option is set (indicating that this is a tape drive), physio( ) arranges that writes to any partial blocks are dealt with by issuing a full block read, updating the data as required, and then writing it back.

Context and synchronization

User context.

Hardware applicability

All

Version applicability

oddi: 1, 2, 2mp, 3, 3mp, 4, 4mp, 5, 5mp, 6, 6mp

Differences between versions

For ODDI releases prior to ODDI 3, the bp argument was either a pointer to a buffer header to be used for the I/O operation or a NULL pointer. The current implementation of physio no longer makes any use of a supplied buffer header, and using it slows the execution of the data transfer because of processing required for backward compatibility.

In earlier releases, it was necessary to call dma_breakup(D3oddi) or pio_breakup(D3oddi) in conjunction with physio( ) for devices that used DMA or programmed I/O, respectively. physio( ) now handles this functionality internally so these calls are not required.

SVR5 DDI compatibility

For DDI drivers prior to version 8, the physiock(D3) function replaces both physio( ) and physck( ). DDI 8 drivers use the do_biostart(D3) function instead.

References

strategy(D2oddi)