device driver 2.4.20 vs. 2.6.9 virtual memory

From: Greg Frinchaboy (greg_at_visionpro.com)
Date: 02/18/05

  • Next message: Hogue, Russ: "SAMBA and XP" 
    To: redhat-list@redhat.com
Date: Fri, 18 Feb 2005 07:35:48 -0800

    We share some memory between user space and the driver by allocating it
    in the driver and mmapping in the user program. The following code has
    been working for couple of years using RH7.3 with the 2.4.20 kernel:

    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? 

    -- 
redhat-list mailing list
unsubscribe mailto:redhat-list-request@redhat.com?subject=unsubscribe
https://www.redhat.com/mailman/listinfo/redhat-list
  • Next message: Hogue, Russ: "SAMBA and XP"
    Loading