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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.
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