Re: [PATCH 3/3] DAX: use pfn_mkwrite to update c/mtime

[Jan Kara <jack@suse.cz>]

On Wed 04-03-15 18:48:06, Boaz Harrosh wrote:
> From: Yigal Korman <yigal@plexistor.com>
> 
> Without this patch, c/mtime is not updated correctly when mmap'ed page is
> first read from and then written to.
> 
> A new xfstest is submitted for testing this (generic/080)
> 
> Signed-off-by: Yigal Korman <yigal@plexistor.com>
> Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
> ---
>  fs/dax.c           | 13 +++++++++++++
>  fs/ext2/file.c     |  1 +
>  fs/ext4/file.c     |  1 +
>  include/linux/fs.h |  1 +
>  4 files changed, 16 insertions(+)
> 
> diff --git a/fs/dax.c b/fs/dax.c
> index ed1619e..cd63adc 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -464,6 +464,19 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
>  EXPORT_SYMBOL_GPL(dax_fault);
>  
>  /**
> + * dax_pfn_mkwrite - handle first write to DAX page
> + * @vma: The virtual memory area where the fault occurred
> + * @vmf: The description of the fault
> + *
> + */
> +int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
> +{
> +	file_update_time(vma->vm_file);
> +	return VM_FAULT_NOPAGE;
> +}
> +EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);
  Hum, you likely want a freeze protection in there as well
(sb_start_pagefault() and sb_end_pagefault()). Don't you?  Otherwise user
could start writing to the page while filesystem is frozen.  That's another
bug you could mention in your description.

								Honza

> +
> +/**
>   * dax_zero_page_range - zero a range within a page of a DAX file
>   * @inode: The file being truncated
>   * @from: The file offset that is being truncated to
> diff --git a/fs/ext2/file.c b/fs/ext2/file.c
> index e317017..866a3ce 100644
> --- a/fs/ext2/file.c
> +++ b/fs/ext2/file.c
> @@ -39,6 +39,7 @@ static int ext2_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  static const struct vm_operations_struct ext2_dax_vm_ops = {
>  	.fault		= ext2_dax_fault,
>  	.page_mkwrite	= ext2_dax_mkwrite,
> +	.pfn_mkwrite	= dax_pfn_mkwrite,
>  };
>  
>  static int ext2_file_mmap(struct file *file, struct vm_area_struct *vma)
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index 33a09da..b43a7a6 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -206,6 +206,7 @@ static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  static const struct vm_operations_struct ext4_dax_vm_ops = {
>  	.fault		= ext4_dax_fault,
>  	.page_mkwrite	= ext4_dax_mkwrite,
> +	.pfn_mkwrite	= dax_pfn_mkwrite,
>  };
>  #else
>  #define ext4_dax_vm_ops	ext4_file_vm_ops
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b4d71b5..24af817 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2597,6 +2597,7 @@ int dax_clear_blocks(struct inode *, sector_t block, long size);
>  int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
>  int dax_truncate_page(struct inode *, loff_t from, get_block_t);
>  int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
> +int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
>  #define dax_mkwrite(vma, vmf, gb)	dax_fault(vma, vmf, gb)
>  
>  #ifdef CONFIG_BLOCK
> -- 
> 1.9.3
> 
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR