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Date:   Thu, 30 Aug 2018 16:56:29 +0900 (JST)
Message-Id: <20180830.165629.1747893038794269821.konishi.ryusuke@lab.ntt.co.jp>
To:     Souptick Joarder <jrdr.linux@gmail.com>
Cc:     willy@infradead.org, viro@zeniv.linux.org.uk, tytso@mit.edu,
        adilger.kernel@dilger.ca, darrick.wong@oracle.com, axboe@kernel.dk,
        ebiggers@google.com, tglx@linutronix.de,
        gregkh@linuxfoundation.org, kemi.wang@intel.com,
        akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-nilfs@vger.kernel.org
Subject: Re: [PATCH] fs: Convert return type int to vm_fault_t
From:   Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
In-Reply-To: <20180828192528.GA24453@jordon-HP-15-Notebook-PC>
References: <20180828192528.GA24453@jordon-HP-15-Notebook-PC>
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On Wed, 29 Aug 2018 00:55:28 +0530, Souptick Joarder wrote:
> Return type for fault handlers  in ext4 and nilfs are
> changed to use vm_fault_t.
> 
> Return type of block_page_mkwrite() is changed from
> int to vm_fault_t. The function signature of
> block_page_mkwrite() is changed to add one new parameter
> int *err. This will provide a way for caller functions
> to get error number along with VM_FAULT return value and
> use it further.
> 
> Return type of block_page_mkwrite_return() is also changed
> to use new vm_fault_t type.
> 
> Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
> ---
>  fs/buffer.c                 | 20 +++++++++++---------
>  fs/ext4/ext4.h              |  4 ++--
>  fs/ext4/inode.c             | 34 ++++++++++++++++++----------------
>  fs/nilfs2/file.c            | 16 ++++++++++------
>  include/linux/buffer_head.h |  7 ++++---
>  5 files changed, 45 insertions(+), 36 deletions(-)
> 
> diff --git a/fs/buffer.c b/fs/buffer.c
> index ebf78ab..aacfc73 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -2487,21 +2487,21 @@ int block_commit_write(struct page *page, unsigned from, unsigned to)
>   * Direct callers of this function should protect against filesystem freezing
>   * using sb_start_pagefault() - sb_end_pagefault() functions.
>   */
> -int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> -			 get_block_t get_block)
> +vm_fault_t block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> +			 get_block_t get_block, int *err)
>  {
>  	struct page *page = vmf->page;
>  	struct inode *inode = file_inode(vma->vm_file);
>  	unsigned long end;
>  	loff_t size;
> -	int ret;
> +	int err1;
>  
>  	lock_page(page);
>  	size = i_size_read(inode);
>  	if ((page->mapping != inode->i_mapping) ||
>  	    (page_offset(page) > size)) {
>  		/* We overload EFAULT to mean page got truncated */
> -		ret = -EFAULT;
> +		err1 = -EFAULT;
>  		goto out_unlock;
>  	}
>  
> @@ -2511,18 +2511,20 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
>  	else
>  		end = PAGE_SIZE;
>  
> -	ret = __block_write_begin(page, 0, end, get_block);
> -	if (!ret)
> -		ret = block_commit_write(page, 0, end);
> +	err1 = __block_write_begin(page, 0, end, get_block);
> +	if (!err1)
> +		err1 = block_commit_write(page, 0, end);
>  
> -	if (unlikely(ret < 0))
> +	if (unlikely(err1 < 0))
>  		goto out_unlock;
> +	*err = err1;
>  	set_page_dirty(page);
>  	wait_for_stable_page(page);
>  	return 0;
>  out_unlock:
>  	unlock_page(page);
> -	return ret;
> +	*err = err1;
> +	return block_page_mkwrite_return(err1);
>  }
>  EXPORT_SYMBOL(block_page_mkwrite);
>  
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 0f0edd1..8506b14 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2469,8 +2469,8 @@ int do_journal_get_write_access(handle_t *handle,
>  extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
>  extern int ext4_zero_partial_blocks(handle_t *handle, struct inode *inode,
>  			     loff_t lstart, loff_t lend);
> -extern int ext4_page_mkwrite(struct vm_fault *vmf);
> -extern int ext4_filemap_fault(struct vm_fault *vmf);
> +extern vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf);
> +extern vm_fault_t ext4_filemap_fault(struct vm_fault *vmf);
>  extern qsize_t *ext4_get_reserved_space(struct inode *inode);
>  extern int ext4_get_projid(struct inode *inode, kprojid_t *projid);
>  extern void ext4_da_update_reserve_space(struct inode *inode,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 82adee7..1062a8e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -6151,39 +6151,40 @@ static int ext4_bh_unmapped(handle_t *handle, struct buffer_head *bh)
>  	return !buffer_mapped(bh);
>  }
>  
> -int ext4_page_mkwrite(struct vm_fault *vmf)
> +vm_fault_t ext4_page_mkwrite(struct vm_fault *vmf)
>  {
>  	struct vm_area_struct *vma = vmf->vma;
>  	struct page *page = vmf->page;
>  	loff_t size;
>  	unsigned long len;
> -	int ret;
> +	vm_fault_t ret;
>  	struct file *file = vma->vm_file;
>  	struct inode *inode = file_inode(file);
>  	struct address_space *mapping = inode->i_mapping;
>  	handle_t *handle;
>  	get_block_t *get_block;
> -	int retries = 0;
> +	int retries = 0, err;
>  
>  	sb_start_pagefault(inode->i_sb);
>  	file_update_time(vma->vm_file);
>  
>  	down_read(&EXT4_I(inode)->i_mmap_sem);
>  
> -	ret = ext4_convert_inline_data(inode);
> -	if (ret)
> +	err = ext4_convert_inline_data(inode);
> +	if (err)
>  		goto out_ret;
>  
> +	err = 0;
>  	/* Delalloc case is easy... */
>  	if (test_opt(inode->i_sb, DELALLOC) &&
>  	    !ext4_should_journal_data(inode) &&
>  	    !ext4_nonda_switch(inode->i_sb)) {
>  		do {
>  			ret = block_page_mkwrite(vma, vmf,
> -						   ext4_da_get_block_prep);
> -		} while (ret == -ENOSPC &&
> +					ext4_da_get_block_prep, &err);
> +		} while (err == -ENOSPC &&
>  		       ext4_should_retry_alloc(inode->i_sb, &retries));
> -		goto out_ret;
> +		goto out;
>  	}
>  
>  	lock_page(page);
> @@ -6226,36 +6227,37 @@ int ext4_page_mkwrite(struct vm_fault *vmf)
>  		ret = VM_FAULT_SIGBUS;
>  		goto out;
>  	}
> -	ret = block_page_mkwrite(vma, vmf, get_block);
> +	err = 0;
> +	ret = block_page_mkwrite(vma, vmf, get_block, &err);
>  	if (!ret && ext4_should_journal_data(inode)) {
>  		if (ext4_walk_page_buffers(handle, page_buffers(page), 0,
>  			  PAGE_SIZE, NULL, do_journal_get_write_access)) {
>  			unlock_page(page);
> -			ret = VM_FAULT_SIGBUS;
>  			ext4_journal_stop(handle);
>  			goto out;
>  		}
>  		ext4_set_inode_state(inode, EXT4_STATE_JDATA);
>  	}
>  	ext4_journal_stop(handle);
> -	if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
> +	if (err == -ENOSPC &&
> +		ext4_should_retry_alloc(inode->i_sb, &retries))
>  		goto retry_alloc;
>  out_ret:
> -	ret = block_page_mkwrite_return(ret);
> +	ret = block_page_mkwrite_return(err);
>  out:
>  	up_read(&EXT4_I(inode)->i_mmap_sem);
>  	sb_end_pagefault(inode->i_sb);
>  	return ret;
>  }
>  
> -int ext4_filemap_fault(struct vm_fault *vmf)
> +vm_fault_t ext4_filemap_fault(struct vm_fault *vmf)
>  {
>  	struct inode *inode = file_inode(vmf->vma->vm_file);
> -	int err;
> +	vm_fault_t ret;
>  
>  	down_read(&EXT4_I(inode)->i_mmap_sem);
> -	err = filemap_fault(vmf);
> +	ret = filemap_fault(vmf);
>  	up_read(&EXT4_I(inode)->i_mmap_sem);
>  
> -	return err;
> +	return ret;
>  }
> diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
> index 7da0fac..58d2a81 100644
> --- a/fs/nilfs2/file.c
> +++ b/fs/nilfs2/file.c
> @@ -57,7 +57,8 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
>  	struct page *page = vmf->page;
>  	struct inode *inode = file_inode(vma->vm_file);
>  	struct nilfs_transaction_info ti;
> -	int ret = 0;
> +	vm_fault_t ret = VM_FAULT_LOCKED;
> +	int err = 0;
>  
>  	if (unlikely(nilfs_near_disk_full(inode->i_sb->s_fs_info)))
>  		return VM_FAULT_SIGBUS; /* -ENOSPC */
> @@ -67,7 +68,7 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
>  	if (page->mapping != inode->i_mapping ||
>  	    page_offset(page) >= i_size_read(inode) || !PageUptodate(page)) {
>  		unlock_page(page);
> -		ret = -EFAULT;	/* make the VM retry the fault */
> +		ret = VM_FAULT_NOPAGE;	/* make the VM retry the fault */
>  		goto out;
>  	}
>  
> @@ -99,13 +100,16 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
>  	/*
>  	 * fill hole blocks
>  	 */
> -	ret = nilfs_transaction_begin(inode->i_sb, &ti, 1);
> +	err = nilfs_transaction_begin(inode->i_sb, &ti, 1);
>  	/* never returns -ENOMEM, but may return -ENOSPC */
> -	if (unlikely(ret))
> +	if (unlikely(err)) {
> +		ret = block_page_mkwrite_return(err);
>  		goto out;
> +	}
>  

> +	err = 0;

This initialization looks unnecessary.  "err" is always zero here.

Regards,
Ryusuke Konishi

>  	file_update_time(vma->vm_file);
> -	ret = block_page_mkwrite(vma, vmf, nilfs_get_block);
> +	ret = block_page_mkwrite(vma, vmf, nilfs_get_block, &err);
>  	if (ret) {
>  		nilfs_transaction_abort(inode->i_sb);
>  		goto out;
> @@ -117,7 +121,7 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
>  	wait_for_stable_page(page);
>   out:
>  	sb_end_pagefault(inode->i_sb);
> -	return block_page_mkwrite_return(ret);
> +	return ret;
>  }
>  
>  static const struct vm_operations_struct nilfs_file_vm_ops = {
> diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
> index 96225a7..e212b13 100644
> --- a/include/linux/buffer_head.h
> +++ b/include/linux/buffer_head.h
> @@ -14,6 +14,7 @@
>  #include <linux/pagemap.h>
>  #include <linux/wait.h>
>  #include <linux/atomic.h>
> +#include <linux/mm_types.h>
>  
>  #ifdef CONFIG_BLOCK
>  
> @@ -239,10 +240,10 @@ int cont_write_begin(struct file *, struct address_space *, loff_t,
>  			get_block_t *, loff_t *);
>  int generic_cont_expand_simple(struct inode *inode, loff_t size);
>  int block_commit_write(struct page *page, unsigned from, unsigned to);
> -int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> -				get_block_t get_block);
> +vm_fault_t block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
> +				get_block_t get_block, int *err);
>  /* Convert errno to return value from ->page_mkwrite() call */
> -static inline int block_page_mkwrite_return(int err)
> +static inline vm_fault_t block_page_mkwrite_return(int err)
>  {
>  	if (err == 0)
>  		return VM_FAULT_LOCKED;
> -- 
> 1.9.1
>