It seems the mux_vma_nopage() operation hadn't been called.
----- Original Message -----
From: yihect
To: kernelnewbie
Cc: yih...@163.com
Sent: Thursday, March 26, 2009 1:48 PM
Subject: question about mapping RAM into user space.
Hi, all:
I'm a newbie of kernel. I'm working on my mux driver in hand, and want to
map some RAM(say, 1024*1024*2 bytes totally)into user space.
Accroding the LDD3 book, I'm using __get_free_pages() which be called in
nopage() operation of struct vm_operations_struct like follow:
/* get page from mux dev, and return it to the user. */
struct page *mux_vma_nopage(struct vm_area_struct *vma,
unsigned long address, int *type)
{
unsigned long offset;
struct mux_dev *dev = vma->vm_private_data;
struct page *page = NOPAGE_SIGBUS;
void *pageptr = NULL; /* default to "missing" */
printk("In mux_vma_nopage ############################################\n"
);
down(&dev->sem);
offset = (address - vma->vm_start) + (vma->vm_pgoff << PAGE_SHIFT);
if (offset >= dev->size) goto out; /* out of range */
/* get page from our dev, get free page if inavialable */
offset >>= PAGE_SHIFT; /* offset is a number of pages */
if (!dev->data[offset])
{
dev->data[offset] = (void *)__get_free_pages(GFP_KERNEL, 0); /* order
must be 0 */
if (!dev->data[offset])
goto out;
memset(dev->data[offset], 0, PAGE_SIZE);
}
pageptr = dev->data[offset];
page = virt_to_page(pageptr);
/* now increment the count */
get_page(page);
if (type)
*type = VM_FAULT_MINOR;
out:
up(&dev->sem);
return page;
}
The mmap() operation of fops is like:
int nc_mux_mmap(struct file *filp, struct vm_area_struct *vma)
{
/* don't do anything here: "nopage" will set up page table entries */
vma->vm_ops = &mux_vm_ops;
vma->vm_flags |= VM_RESERVED;
vma->vm_private_data = filp->private_data;
mux_vma_open(vma);
return 0;
}
When I test useing code :
address=mmap(0, len, PROT_READ, MAP_FILE | MAP_PRIVATE, fd, offset);
if (address == (void *)-1) {
fprintf(stderr,"%s: mmap(): %s\n",argv[0],strerror(errno));
exit(1);
}
strcpy((char *)address, "hello, world.");
It gives me msg of "segmen fault":
/mnt/nfs $ ./mapper /dev/mux_dev 0x0 0x400[J
SDVR22xxMX MUX Device Driver Open...
pgd = c01a4000
[40018000] *pgd=001e8031, *pte=00000000, *ppte=00000000
Pid: 151, comm: mapper
CPU: 0
PC is at 0x4008b9f8
LR is at 0x8960
pc : [<4008b9f8>] lr : [<00008960>] Tainted: P
sp : bec9a64c ip : 4008b9ec fp : bec9ae88
r10: 40133000 r9 : 00000000 r8 : 00008738
r7 : 00000004 r6 : 00008b3c r5 : 00008ad8 r4 : bec9aeb4
r3 : 00000068 r2 : 4000f3c3 r1 : 00008c3d r0 : 40018000
Flags: nZCv IRQs on FIQs on Mode USER_32 Segment user
Control: 397F Table: 001A4000 DAC: 00000015
[<c052e7d8>] (show_regs+0x0/0x4c) from [<c0533bcc>]
(__do_user_fault+0x5c/0xa4)
r4 = C0039820
[<c0533b70>] (__do_user_fault+0x0/0xa4) from [<c0533e98>]
(do_page_fault+0x218/0x250)
r7 = C05240CC r6 = C0047FB0 r5 = C0039820 r4 = FFFFFFEB
[<c0533c80>] (do_page_fault+0x0/0x250) from [<c053401c>]
(do_DataAbort+0x3c/0xa0)
[<c0533fe0>] (do_DataAbort+0x0/0xa0) from [<c052c908>]
(ret_from_exception+0x0/0x10)
r8 = 00008738 r7 = 00000004 r6 = 00008B3C r5 = 00008AD8
r4 = FFFFFFFF
SDVR22xxMX MUX Device Driver Release...
Segmentation fault
Platform is arm and kernel version is 2.6.14, I don'e know how to do nextly,
is somebody have any suggestion? thanks.
