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SubjectRe: [PATCH v6 07/22] Replace the XIP page fault handler with the DAX page fault handler
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On Tue, 2014-02-25 at 09:18 -0500, Matthew Wilcox wrote:
> Instead of calling aops->get_xip_mem from the fault handler, the
> filesystem passes a get_block_t that is used to find the appropriate
> blocks.
:
> +static int do_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
> + get_block_t get_block)
> +{
> + struct file *file = vma->vm_file;
> + struct inode *inode = file_inode(file);
> + struct address_space *mapping = file->f_mapping;
> + struct buffer_head bh;
> + unsigned long vaddr = (unsigned long)vmf->virtual_address;
> + sector_t block;
> + pgoff_t size;
> + unsigned long pfn;
> + int error;
> +
> + size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + if (vmf->pgoff >= size)
> + return VM_FAULT_SIGBUS;
> +
> + memset(&bh, 0, sizeof(bh));
> + block = (sector_t)vmf->pgoff << (PAGE_SHIFT - inode->i_blkbits);
> + bh.b_size = PAGE_SIZE;
> + error = get_block(inode, block, &bh, 0);
> + if (error || bh.b_size < PAGE_SIZE)
> + return VM_FAULT_SIGBUS;

I am learning the code and have some questions. The original code,
xip_file_fault(), jumps to found: and calls vm_insert_mixed() when
get_xip_mem(,,0,,) succeeded. If get_xip_mem() returns -ENODATA, it
calls either get_xip_mem(,,1,,) or xip_sparse_page(). In this new
function, it looks to me that get_block(,,,0) returns 0 for both cases
(success and -ENODATA previously), which are dealt in the same way. Is
that right? If so, is there any reason for the change? Also, isn't it
possible to call get_block(,,,1) even if get_block(,,,0) found a block?

Thanks,
-Toshi

> +
> + if (!buffer_written(&bh) && !vmf->cow_page) {
> + if (vmf->flags & FAULT_FLAG_WRITE) {
> + error = get_block(inode, block, &bh, 1);
> + if (error || bh.b_size < PAGE_SIZE)
> + return VM_FAULT_SIGBUS;
> + } else {
> + return dax_load_hole(mapping, vmf);
> + }
> + }
> +




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