In the kernel driver:
typedef struct shared {
unsigned long event_addr;
time_t ntimes_stamp;
} OurShared;dev_sp->shared_host_mem is a pointer to an OurShared;
static int
alloc_usr_shared(OurSoftDev *our_dev_sp)
{
unsigned long virt_addr;
dev_sp->shared_host_mem = (OurShared *)kmalloc(SOME_SIZE, GFP_KERNEL); /* SOME_SIZE is usually PAGE_SIZE */
if (dev_sp->shared_host_mem == NULL)
return error, etc.
for (virt_addr = (unsigned long) dev_sp->shared_host_mem;
virt_addr < (unsigned long) dev_sp->shared_host_mem + SOME_SIZE;
virt_addr += PAGE_SIZE)
{
/* reserve all pages to make them remapable */
mem_map_reserve(virt_to_page(virt_addr));
}
return 0;
}mem_map_reserve is a macro in wrapper.h to set the Pg_reserved bit.
In the user space:
void *addr = mmap(0, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
_kernel._our_dev_common = reinterpret_cast<OurShared *>(addr);
gives us access to this "common or shared memory". One of purposes of this shared memory is to keep track of how many times an event occurred. The "event" gets set to 0 in usr space and counted up every interrupt in kernel space. The user program queries the event count from time to time.
Using Fedora
In 2.6, wrapper.h is gone. However, SetPageReserved does the same thing a mem_map_reserve, so I used the SetPageReserved macro.
When I try to run the system in 2.6, the system crashes hard - sometimes I get an oops, Unable to handle Kernel NULL pointer dereference virtual address 00000004. Other times the system locks up before it can log a message.
I placed a printk in the interrupt handler and saw the shared memory location which should be 0 to start is some random number. This leads me to believe the mechanism using kmalloc and trying to lock it down using mmap no longer works in the 2.6 kernel.
Does anyone know how to lock some "virtual" shared memory between user space and kernel space in the 2.6 kernel?
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