lkml.org 
[lkml]   [2008]   [Oct]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: Questions about mmap
    Date
    From
    On Tue, 7 Oct 2008, Thiago Lacerda wrote:

    > Thank you Stefan.... by I'd something more concrete.
    >
    > I'm trying to do like this:
    >
    > //Code of the char device
    > unsigned int **test;
    > static int device_mmap(struct file *filp, struct vm_area_struct *vma) {
    > printk(KERN_INFO"Calling mmap\n");
    > vma->vm_flags |= VM_LOCKED;
    > if(remap_pfn_range(vma, vma->vm_start,
    > virt_to_phys((void*)((unsigned long)test)) >> PAGE_SHIFT, vma->vm_end
    > - vma->vm_start, PAGE_SHARED))
    > return -EAGAIN;
    > printk(KERN_INFO"mmap returned\n");
    > return 0;
    > }
    >
    > static int __init testeInit(void) {
    > /* after creating char device and registering it*/
    > ...
    > ....
    > test = (unsigned int**) kmalloc(sizeof(unsigned int*)*1024, GFP_KERNEL);
    > int i;
    > for(i = 0; i < 1024; i++)
    > test[i] = NULL;
    >
    > unsigned int* temp1 = (unsigned int*) kmalloc(sizeof(unsigned int), GFP_KERNEL);
    > (*temp1) = 9;
    > test[0] = temp1;
    > return 0;
    > }
    >
    > and at user program:
    >
    > int main() {
    > int fd;
    >
    > unsigned int **mptr;
    > size_t size = 1024*sizeof(unsigned int*);
    > fd = open("/dev/myDev", O_RDWR);
    > if( fd == -1) {
    > printf("open error...\n");
    > exit(0);
    > }
    >
    > mptr = mmap(0, sizeof(unsigned int*)*1024, PROT_READ | PROT_WRITE,
    > MAP_FILE | MAP_SHARED, fd, 0);
    > if(mptr == MAP_FAILED) {
    > printf("mmap() failed\n");
    > exit(1);
    > }
    > printf("teste[0]: %u\n", *mptr[0]);
    > munmap(mptr, size);
    > close(fd);
    > return 0;
    > }
    >
    > It's not working, could you tell me what am I doing wrong? It is for
    > my undergraduate thesis ans it is really driving me mad.
    >
    > I hope that you can help me.
    >
    > best regards.
    >
    > --
    > Thiago de Barros Lacerda

    It looks like you are trying to memory-map a pointer that
    you expect to de-reference in user space. Perhaps you can
    tell us what it is that you are trying to do. You need
    to use copy/to/from_user to copy things from or to the kernel.

    Attempts to dereference kernel data will fail because the
    segments for kernel data or code are not the same as user
    data or code.


    Cheers,
    Dick Johnson
    Penguin : Linux version 2.6.25.17 on an i686 machine (4786.81 BogoMips).
    My book : http://www.AbominableFirebug.com/
    _


    ****************************************************************
    The information transmitted in this message is confidential and may be privileged. Any review, retransmission, dissemination, or other use of this information by persons or entities other than the intended recipient is prohibited. If you are not the intended recipient, please notify Analogic Corporation immediately - by replying to this message or by sending an email to DeliveryErrors@analogic.com - and destroy all copies of this information, including any attachments, without reading or disclosing them.

    Thank you.


    \
     
     \ /
      Last update: 2008-10-07 22:45    [W:0.028 / U:120.024 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site