Hi,
I got solution to my problem from linux-kernel
mailing list .
I m posting here for future reference.
On Tue, 1 Mar 2005, Prakash Bhurke wrote:
> I am trying to map a vmalloc kernel buffer to user
> space using remap_page_range(). In my module, this
> function returns success if we call mmap() from user
> space, but i can not access content of vmalloc
buffer
> from user space. Pointer returned by mmap() syscall
> seems pointing to other memory page which contains
> zeros. I am using linux 2.6.10 kernel on Pentium 4
> system.
Look for "rvmalloc" in various drivers in the kernel
source tree:
you must SetPageReserved before remap_pfn_range (or
remap_page_range)
agrees to map the page, and ClearPageReserved before
freeing after.
Regards,
--- Prakash Bhurke <[EMAIL PROTECTED]> wrote:
> Hi ,
>
> I am facing a problem -- memory mapping of proc
> entry into user space using mmap syscall.
> I have written a module which creates a proc entry
> &
> provides read, write, mmap, etc.
> Normal read, write etc file operation works, but
> mmap is not working.
> I am trying to map a vmalloc kernel buffer to user
> space using remap_page_range(). In my module, this
> function returns success if we call mmap() from user
> space, but i can not access content of vmalloc
> buffer
> from user space. Pointer returned by mmap() syscall
> seems pointing to other memory page which contains
> zeros. I am using linux 2.6.10 kernel on Pentium 4
> system.
>
> here is code of module_mmap();
> static inline unsigned long kvirt_to_pa(unsigned
> long
> adr)
> {
> unsigned long kva, ret;
>
> kva = (unsigned long)
> page_address(vmalloc_to_page((void *)adr));
> kva |= adr & (PAGE_SIZE-1); /* restore the offset
> */
> ret = __pa(kva);
> return ret;
> }
>
> static int module_mmap(struct file *file, struct
> vm_area_struct *vma)
> {
> unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;
> unsigned long len = vma->vm_end - vma->vm_start;
> unsigned long pos = (unsigned long) test_tsc +
> offset;
>
> printk(KERN_INFO "PROCINFO : in mmap started,
> length
> = %ld\n", len);
>
> if (!tscinfo)
> return -ENODEV;
>
> if ((offset + len) >
> PAGE_ALIGN(sizeof(sizeof(struct
> test_tsc_info)))))
> return -ENXIO;
>
> if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) ==
> (VM_SHARED|VM_WRITE)) {
> printk("PROCINFO : in mmap attempt to write to
> mapping\n");
> return -EPERM;
> }
>
> vma->vm_flags |= VM_SHM | VM_LOCKED ;
>
> if (remap_pfn_range(vma, vma->vm_start,
> kvirt_to_pa(pos) >> PAGE_SHIFT, \
> len, vma->vm_page_prot)) {
> printk(KERN_INFO "PROCINFO : in mmap
> remap_pfn_range
> returns error\n");
> return -EAGAIN;
> }
>
> printk(KERN_INFO "PROCINFO : in mmap ret 0 end\n");
>
> return 0;
> }
>
> From user space program i mapping kernel memory like
> this
> proc_fd = open("/proc/"PROC_ENTRY_FILENAME,
> O_RDONLY);
> mem_base = mmap(NULL, sizeof(struct test_tsc_info),
> PROT_READ, MAP_SHARED, proc_fd, 0);
>
> Please let me know what wrong thins i m doing.
>
> Regards,
> Prakash.
>
>
>
>
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