2013/6/11 Michael Holzheu <holzheu at linux.vnet.ibm.com>:
> On Mon, 10 Jun 2013 22:40:24 +0900
> HATAYAMA Daisuke <d.hatayama at gmail.com> wrote:
>
>> 2013/6/8 Michael Holzheu <holzheu at linux.vnet.ibm.com>:
>> <cut>
>> > @@ -225,6 +251,56 @@ static ssize_t read_vmcore(struct file *file, char __user *buffer,
>> > return acc;
>> > }
>> >
>> > +static ssize_t read_vmcore(struct file *file, char __user *buffer,
>> > + size_t buflen, loff_t *fpos)
>> > +{
>> > + return __read_vmcore(buffer, buflen, fpos, 1);
>> > +}
>> > +
>> > +/*
>> > + * The vmcore fault handler uses the page cache and fills data using the
>> > + * standard __vmcore_read() function.
>> > + */
>> > +static int mmap_vmcore_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>> > +{
>> > + struct address_space *mapping = vma->vm_private_data;
>> > + pgoff_t index = vmf->pgoff;
>> > + struct page *page;
>> > + loff_t src;
>> > + char *buf;
>> > + int rc;
>> > +
>> > +find_page:
>> > + page = find_lock_page(mapping, index);
>> > + if (page) {
>> > + unlock_page(page);
>> > + rc = VM_FAULT_MINOR;
>> > + } else {
>> > + page = page_cache_alloc_cold(mapping);
>> > + if (!page)
>> > + return VM_FAULT_OOM;
>> > + rc = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
>> > + if (rc) {
>> > + page_cache_release(page);
>> > + if (rc == -EEXIST)
>> > + goto find_page;
>> > + /* Probably ENOMEM for radix tree node */
>> > + return VM_FAULT_OOM;
>> > + }
>> > + buf = (void *) (page_to_pfn(page) << PAGE_SHIFT);
>> > + src = index << PAGE_CACHE_SHIFT;
>> > + __read_vmcore(buf, PAGE_SIZE, &src, 0);
>> > + unlock_page(page);
>> > + rc = VM_FAULT_MAJOR;
>> > + }
>> > + vmf->page = page;
>> > + return rc;
>> > +}
>>
>> How about reusing find_or_create_page()?
>
> The function would then look like the following:
>
> static int mmap_vmcore_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> struct address_space *mapping = vma->vm_private_data;
> pgoff_t index = vmf->pgoff;
> struct page *page;
> loff_t src;
> char *buf;
>
> page = find_or_create_page(mapping, index, GFP_KERNEL);
> if (!page)
> return VM_FAULT_OOM;
> src = index << PAGE_CACHE_SHIFT;
> buf = (void *) (page_to_pfn(page) << PAGE_SHIFT);
> __read_vmcore(buf, PAGE_SIZE, &src, 0);
> unlock_page(page);
> vmf->page = page;
> return 0;
> }
>
> I agree that this makes the function simpler but we have to copy
> the page also if it has already been filled, correct?
>
You can use for the purpose PG_uptodate flag.
> But since normally only one process uses /proc/vmcore this might be
> acceptable.
>
> BTW: I also removed the VM_FAULT_MAJOR/MINOR because I think the fault
> handler should return 0 if a page has been found.
>
> Michael
>
Thanks.
HATAYAMA, Daisuke
