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

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Message-ID: <571599BE.7090202@hpe.com>
Date:	Mon, 18 Apr 2016 22:36:46 -0400
From:	Toshi Kani <toshi.kani@....com>
To:	Jan Kara <jack@...e.cz>
Cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"willy@...ux.intel.com" <willy@...ux.intel.com>,
	"ross.zwisler@...ux.intel.com" <ross.zwisler@...ux.intel.com>,
	"kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"david@...morbit.com" <david@...morbit.com>,
	"tytso@....edu" <tytso@....edu>,
	"adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/2] dax: add dax_get_unmapped_area for pmd mappings

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