linux-ext4 - Re: [PATCH v3 2/3] dax: change bdev_dax_supported() to support boolean returns

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Date:   Tue, 13 Feb 2018 13:43:49 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        darrick.wong@...cle.com, linux-nvdimm@...ts.01.org,
        david@...morbit.com, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, dan.j.williams@...el.com
Subject: Re: [PATCH v3 2/3] dax: change bdev_dax_supported() to support
 boolean returns

On Tue, Feb 13, 2018 at 01:35:19PM -0700, Dave Jiang wrote:
> 
> 
> On 02/13/2018 01:31 PM, Ross Zwisler wrote:
> > On Thu, Feb 08, 2018 at 05:38:19PM -0700, Dave Jiang wrote:
> >> The function return values are confusing with the way the function is
> >> named. We expect a true or false return value but it actually returns
> >> 0/-errno.  This makes the code very confusing. Changing the return values
> >> to return a bool where if DAX is supported then return true and no DAX
> >> support returns false.
> >>
> >> Signed-off-by: Dave Jiang <dave.jiang@...el.com>
> >> ---
> > 
> >> diff --git a/fs/ext2/super.c b/fs/ext2/super.c
> >> index 655699321c45..636b9c5e1bff 100644
> >> --- a/fs/ext2/super.c
> >> +++ b/fs/ext2/super.c
> >> @@ -958,9 +958,10 @@ static int ext2_fill_super(struct super_block *sb, void *data, int silent)
> >>  	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
> >>  
> >>  	if (sbi->s_mount_opt & EXT2_MOUNT_DAX) {
> >> -		err = sb_dax_supported(sb, blocksize);
> >> -		if (err)
> >> +		if(!sb_dax_supported(sb, blocksize)) {
> >> +			err = -EIO;
> > 
> > No need to set 'err' here.  This is just a temporary variable used for some
> > local checks later in the function.  'ret' is the value that will be returned,
> > and that is already initialized to -EINVAL which should be fine.
> 
> Change ret to -EIO instead to set the correct error return code?

I'm not sure that -EIO is the 'correct' return code.  The old
sb_dax_supported() code could have returned -EINVAL, -EOPNOTSUPP or -EIO,
based on what went wrong.  All the other error cases in this function just
goto failed_mount without messing with 'ret', and we should probably do the
same.