Messages in this thread |  | | Date | Fri, 04 May 2001 13:57:22 +0100 | From | Terry Barnaby <> | Subject | Question on mmap(2) with kernel alocated memory |
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I am trying to mmap() into user space a kernel buffer and am having problems. I have a simple test example, can someone please tell me what I have got wrong ?
In a driver I do: uint* kva;
kva = (uint*)kmalloc(4096, GFP_KERNEL); *kva = 0x11223344; printk("Address: %p %lx %x\n", kva, virt_to_phys(kva), *kva);
Now in some simple user program I do:
#include <stdio.h> #include <string.h> #include <stdlib.h> #include <sys/mman.h> #include <fcntl.h>
int main(int argc, char** argv){ int fm; char* p; uint* pi; uint v; uint add = 0x74b000;
if((fm = open("/dev/mem", O_RDWR)) < 0) return 1;
p = mmap(0, 128 * 1024 * 1024, PROT_READ|PROT_WRITE, MAP_SHARED, fm, 0); printf("Mapped: %p\n", p);
lseek(fm, add, SEEK_SET); read(fm, &v, sizeof(v)); printf("V: %x\n", v);
pi = (uint*)(p + add); printf("Vmmap: %p %x\n", pi, *pi);
close(fm); return 0; }
The value of add is hardcoded to the value printed for the physical address in the drivers prink routine. The lseek/read from the /dev/mem device yields the value 0x11223344. However the mmap method also on /dev/mem yields the value 0.
Whats wrong with my mmap() or kalloc() ?
Terry
-- Dr Terry Barnaby BEAM Ltd Phone: +44 1454 324512 Northavon Business Center, Dean Rd Fax: +44 1454 313172 Yate, Bristol, BS37 5NH, UK Email: terry@beam.demon.co.uk Web: www.beam.demon.co.uk BEAM for: Visually Impaired X-Terminals, Parallel Processing, Software Dev "Tandems are twice the fun !"
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