svatophys(9r)svatophys(9r)NAMEsvatophys - General: Converts a system virtual address to a physical
address
SYNOPSIS
kern_return_t svatophys(
vm_offset_t kern_addr,
vm_offset_t *phys_addr );
ARGUMENTS
Specifies the kernel virtual address. Specifies a pointer to the phys‐
ical address to be filled in.
DESCRIPTION
The svatophys routine converts a system virtual address to the corre‐
sponding physical address. All address and data structure manipulation
done within the kernel is performed using system virtual addresses.
Typically, system virtual addresses are a means of mapping physical
memory and I/O space, which often consists of device registers and DMA
buffers. In contrast to this, devices are usually unaware of any vir‐
tual addressing and for this reason use physical addresses. You use the
svatophys routine to perform this address translation.
As an example of where you can use this address translation, a disk
device driver can use DMA buffers to transfer blocks of data to the
disk (for the case of a write operation). The data to be written to
disk is present in system memory at a system virtual address known to
the driver. To initiate the DMA operation, the disk driver can set up a
command packet to specify a write operation to the underlying disk con‐
troller hardware. This write command packet contains (among other
things) the location of the DMA buffer as a physical address and the
length of the buffer. Here, the driver calls the svatophys routine to
translate the system virtual address of the DMA buffer to a physical
address in the command packet issued to the disk driver.
RETURN VALUES
The svatophys routine returns the following: The address translation
has been completed successfully. Unable to perform address transla‐
tion. This value indicates that the address specified by the kern_addr
argument is not a valid kernel or system virtual address.
svatophys(9r)
