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);
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;
}
>
> int
> init_module(void){
> ...
> kmalloc_area=kmalloc(LEN,GFP_USER);
> strncpy(kmalloc_area,init_msg,sizeof(init_msg));
> ...
> }
found the problem (naturally after posting....) - forgot to mark
the page as reserved...
struct page *page;
kmalloc_area=kmalloc(LEN,GFP_USER);
page = virt_to_page(kmalloc_area);
mem_map_reserve(page);
memcpy(kmalloc_area,msg,sizeof(msg));
hofrat
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;
> }
> -
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