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?
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
