unmap(D2X)unmap(D2X)NAME
unmap - support virtual unmapping for memory-mapped device
SYNOPSIS
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/ddi.h>
#include <ksys/ddmap.h>
int prefixunmap(dev_t dev, vhandl_t *vt);
Arguments
dev Device whose memory is to be mapped.
vt Handle to caller's virtual address space
DESCRIPTION
To unmap a device, the user program calls munmap(2) system call. After
performing device-independent unmapping in the user's space, the munmap
system call calls the driver's prefixunmap to remove the mapping.
Return Values
On success, 0 is returned. An error number is returned on failure.
USAGE
If a driver provides a map(D2X) routine but does not provide an unmapping
routine, the munmap system call returns the ENODEV error condition to the
user. Therefore, it is a good idea for all drivers to provide a dummy
unmapping routine even if your driver does not need to perform any action
to unmap the device.
Synchronization Constraints
The unmap routine has user context and can sleep.
There are significant restrictions imposed on unmap routines that affect
drivers that perform their own synchronization. When the unmap function
is called, the address space for the process that is doing the call is
locked. When an address space is locked, no other mapping or unmapping
can take place and NO page faults can be serviced for the process. This
can cause problems if the process is multi-threaded - one thread can be
attempting to unmap the device and another thread can be accessing the
driver through some other entry point (e.g. ioctl). If the thread that
is accessing the driver via ioctl locks a driver specific lock, and then
calls e.g. copyin, and if the data to be copied in causes a page fault,
then the page fault code will attempt to lock the address space lock. If,
at the same time, another thread is attempting to unmap the device, and
the unmap routine grabs the driver lock, an AB-BA deadlock can occur
which will require re-booting the system to clear. The safest way around
this is to make sure that the driver never calls copyin or copyout while
holding a driver lock and is used by the unmap routine.
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unmap(D2X)unmap(D2X)REFERENCESmap(D2X), v_getaddr(D3X), v_getlen(D3X), v_gethandle(D3X), v_mapphys(D3X)
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