linux-kernel - Re: [PATCH v2] fs: Convert return type int to vm_fault

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Message-ID: <20180903044949.GB17856@bombadil.infradead.org>
Date:   Sun, 2 Sep 2018 21:49:49 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     akpm@...ux-foundation.org, konishi.ryusuke@....ntt.co.jp,
        viro@...iv.linux.org.uk, tytso@....edu, adilger.kernel@...ger.ca,
        axboe@...nel.dk, darrick.wong@...cle.com, ebiggers@...gle.com,
        pombredanne@...b.com, agruenba@...hat.com,
        gregkh@...uxfoundation.org, kemi.wang@...el.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-nilfs@...r.kernel.org
Subject: Re: [PATCH v2] fs: Convert return type int to vm_fault_t

On Thu, Aug 30, 2018 at 10:55:47PM +0530, Souptick Joarder wrote:
> +vm_fault_t block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> +			 get_block_t get_block, int *err)

I don't like returning both the errno and the vm_fault_t.  To me that's a
sign we need to rethink this interface.

I have two suggestions.  First, we could allocate a new VM_FAULT_NOSPC
bit.  Second, we could repurpose one of the existing bits, such as
VM_FAULT_RETRY for this purpose.

> -int ext4_page_mkwrite(struct vm_fault *vmf)
> +vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)

I also think perhaps we could start by _not_ converting block_page_mkwrite().
Just convert ext4_page_mkwrite(), and save converting block_page_mkwrite()
for later.