Messages in this thread | | | From | Zhonghua Dai <> | Subject | Re: mmap question | Date | Tue, 24 Sep 2002 17:37:53 +0800 |
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On Tuesday 24 September 2002 15:26, Der Herr Hofrat wrote: > Hi ! > > trying to write up a simple mmap for a pseudo device that accesses a > kmalloc'ed area. > > The driver is a character driver that only has mmap implemented - the > kmalloc is done in init module and the pointer to the buffer is in global > context. I expected to be able to write to the mmap'ed area from user-space > but it never shows up in kernel space (the printk in driver_mmap always > shows the init_msg passed in init_module). > > the basic framework I'm using is below - can anybody point me to an > obvious error or to some docs that would explain how to share an kmalloc'ed > area with user-space via mmap ? > > thx ! > hofrat > > ---driver--- > char *kmalloc_area; > ... > static int > driver_mmap(struct file *file, > struct vm_area_struct *vma) > { > vma->vm_flags |= VM_LOCKED|VM_SHARED; > > printk("message buffer: %s\",kmalloc_area); > remap_page_range(vma->vm_start, > virt_to_phys(kmalloc_area), > LEN, > PAGE_SHARED);
Before memory can be exported into userspace, the reserved bit must be set. Call mem_map_reserve() prior to remap_page_range().
good luck.
> return 0; > } > > static struct file_operations simple_fops={ > mmap: driver_mmap, > }; > > int > init_module(void){ > ... > kmalloc_area=kmalloc(LEN,GFP_USER); > strncpy(kmalloc_area,init_msg,sizeof(init_msg)); > ... > } > > ---user-app--- > > int main(void) > { > int fd; > char msg[]="some message - should appear in kernel space"; > unsigned int *addr; > > if((fd=open("/dev/simple-device", O_RDWR))<0) > addr = mmap(0, LEN, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); > memset(addr,0,LEN); > strncpy(addr,msg,sizeof(msg)); > return 0; > } > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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