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SubjectRe: Questions about mmap
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.

On Sun, Oct 5, 2008 at 11:01 AM, Stefan Richter
<stefanr@s5r6.in-berlin.de> wrote:
>
> Thiago Lacerda wrote:
> > typedef struct hashtable {
> > flow_t *hashBuckets[X]; // X is a natural number
> > unsigned int size;
> > } Hastable;
> >
> >
> > So, my question is: Can I mmap the hashtable struct and access
> > directly from userspace? I'm afraid that this could turn on mess
> > because of the array of pointers.
> > If it's possible, does anyone know a piece of code that can match my
> > problem? I've been googling and I just find codes dealing with structs
> > itself, not pointers.
>
> If you require portability, you can only use integer types of fixed size
> in kernel<->userspace ABIs. Pointers can then be exchanged as __u64
> under the assumption that pointers not wider than 64 bits. See for
> example the FW_CDEV_IOC_QUEUE_ISO ioctl in include/linux/firewire-cdev.h.
> --
> Stefan Richter
> -=====-==--- =-=- --=-=
> http://arcgraph.de/sr/


--
Thiago de Barros Lacerda
Computer Science Undergraduate Student - CIn/UFPE - 2004.2
Researcher/Software Developer - GPRT - Networking and
Telecommunications Research Group


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