linux-kernel - Re: [PATCH v3 1/2] dax: add dax_get_unmapped

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Message-ID: <20160418204708.GB17889@quack2.suse.cz>
Date:	Mon, 18 Apr 2016 22:47:08 +0200
From:	Jan Kara <jack@...e.cz>
To:	Toshi Kani <toshi.kani@....com>
Cc:	akpm@...ux-foundation.org, dan.j.williams@...el.com,
	viro@...iv.linux.org.uk, willy@...ux.intel.com,
	ross.zwisler@...ux.intel.com, kirill.shutemov@...ux.intel.com,
	david@...morbit.com, jack@...e.cz, tytso@....edu,
	adilger.kernel@...ger.ca, linux-nvdimm@...ts.01.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] dax: add dax_get_unmapped_area for pmd mappings

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.

> +	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...

> +	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).

> +		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.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR