On Thu, Sep 21, 2006 at 09:02:37PM +1000, Michael Ellerman wrote:
> On Thu, 2006-09-21 at 10:07 +0530, Sachin P. Sant wrote:
> > Hi
> >
> > While using dd command to retrive the dump from /dev/oldmem, there comes
> > a rare case where pfn value is zero. In this case the __ioremap() call
> > returns
> > NULL and hence copying fails.
> >
> > # dd if=/dev/oldmem of=/dev/null
> > dd: reading `/dev/oldmem': Bad address
> > 0+0 records in
> > 0+0 records out
> > 0 bytes (0 B) copied, 0.000121 seconds, 0.0 kB/s
> >
> > Attached is a patch to fix this problem. During such rare cases don't call
> > __ioremap() to do the address translation, instead use __va() .
>
> It's not really rare, it's just when we're reading /dev/oldmem directly.
>
> We can actually use the __va() trick for the whole linear mapping rather
> than just pfn 0, which saves the ioremap. We also shouldn't really be
> trying to iounmap(__va(0)).
>
Makes sense. We can take advantage of linear mappings mapped till max_pfn
and avoid ioremap().
> +
> +static size_t copy_oldmem_vaddr(void *vaddr, char *buf, size_t csize,
> + unsigned long offset, int userbuf)
> +{
> + if (userbuf) {
> + if (copy_to_user((char __user *)buf, (vaddr + offset), csize)) {
> + return -EFAULT;
> + }
Probably you can get rid of above pair of braces as there is only single
statement under if.
>
> - if (userbuf) {
> - if (copy_to_user((char __user *)buf, (vaddr + offset), csize)) {
> - iounmap(vaddr);
> - return -EFAULT;
> - }
> - } else
> - memcpy(buf, (vaddr + offset), csize);
> + if (pfn < max_pfn) {
Should this be (pfn <= max_pfn) ?
-Vivek
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