Re: [PATCH v3 1/2] dax: add dax_get_unmapped_area for pmd mappings

[Toshi Kani]

On 4/18/2016 4:47 PM, Jan Kara wrote:
> On Thu 14-04-16 10:48:30, Toshi Kani wrote:
> > +
> > +/**
> > + * dax_get_unmapped_area - handle get_unmapped_area for a DAX file
> > + * @filp: The file being mmap'd, if not NULL
> > + * @addr: The mmap address. If NULL, the kernel assigns the address
> > + * @len: The mmap size in bytes
> > + * @pgoff: The page offset in the file where the mapping starts from.
> > + * @flags: The mmap flags
> > + *
> > + * This function can be called by a filesystem for get_unmapped_area().
> > + * When a target file is a DAX file, it aligns the mmap address at the
> > + * beginning of the file by the pmd size.
> > + */
> > +unsigned long dax_get_unmapped_area(struct file *filp, unsigned long addr,
> > +		unsigned long len, unsigned long pgoff, unsigned long flags)
> > +{
> > +	unsigned long off, off_end, off_pmd, len_pmd, addr_pmd;
> I think we need to use 'loff_t' for the offsets for things to work on
> 32-bits.

Agreed. Will change to loff_t.

> > +	if (!IS_ENABLED(CONFIG_FS_DAX_PMD) ||
> > +	    !filp || addr || !IS_DAX(filp->f_mapping->host))
> > +		goto out;
> > +
> > +	off = pgoff << PAGE_SHIFT;
> And here we need to type to loff_t before the shift...

Right.

> > +	off_end = off + len;
> > +	off_pmd = round_up(off, PMD_SIZE);  /* pmd-aligned offset */
> > +
> > +	if ((off_end <= off_pmd) || ((off_end - off_pmd) < PMD_SIZE))
> None of these parenthesis is actually needed (and IMHO they make the code
> less readable, not more).

OK.  Will remove the parenthesis.

> > +		goto out;
> > +
> > +	len_pmd = len + PMD_SIZE;
> > +	if ((off + len_pmd) < off)
> > +		goto out;
> > +
> > +	addr_pmd = current->mm->get_unmapped_area(filp, addr, len_pmd,
> > +						  pgoff, flags);
> > +	if (!IS_ERR_VALUE(addr_pmd)) {
> > +		addr_pmd += (off - addr_pmd) & (PMD_SIZE - 1);
> > +		return addr_pmd;
> Otherwise the patch looks good to me.

Great. Thanks Jan!
-Toshi