linux-ext4 - Re: [PATCH 11/11] dax: Rip out get

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Date:   Wed, 16 Nov 2016 11:11:50 -0700
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        Christoph Hellwig <hch@...radead.org>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>
Subject: Re: [PATCH 11/11] dax: Rip out get_block based IO support

On Tue, Nov 08, 2016 at 12:08:17PM +0100, Jan Kara wrote:
> No one uses functions using the get_block callback anymore. Rip them
> out and update documentation.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
>  Documentation/filesystems/dax.txt |  21 ++-
>  fs/dax.c                          | 315 --------------------------------------
>  include/linux/dax.h               |  12 --
>  3 files changed, 10 insertions(+), 338 deletions(-)
> 
> diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
> index 23d18b8a49d5..b870867d0321 100644
> --- a/Documentation/filesystems/dax.txt
> +++ b/Documentation/filesystems/dax.txt
> @@ -58,22 +58,21 @@ Implementation Tips for Filesystem Writers
>  Filesystem support consists of
>  - adding support to mark inodes as being DAX by setting the S_DAX flag in
>    i_flags
> -- implementing the direct_IO address space operation, and calling
> -  dax_do_io() instead of blockdev_direct_IO() if S_DAX is set
> +- implementing ->read_iter and ->write_iter operations which use dax_iomap_rw()
> +  when inode has S_DAX flag set
>  - implementing an mmap file operation for DAX files which sets the
>    VM_MIXEDMAP and VM_HUGEPAGE flags on the VMA, and setting the vm_ops to
> -  include handlers for fault, pmd_fault and page_mkwrite (which should
> -  probably call dax_fault(), dax_pmd_fault() and dax_mkwrite(), passing the
> -  appropriate get_block() callback)
> -- calling dax_truncate_page() instead of block_truncate_page() for DAX files
> -- calling dax_zero_page_range() instead of zero_user() for DAX files
> +  include handlers for fault, pmd_fault, page_mkwrite, pfn_mkwrite (which
> +  should probably call dax_iomap_fault(), dax_iomap_pmd_fault(),
> +  dax_pfn_mkwrite() passing the appropriate iomap operations)

One tiny nit - the list of operations that the filesystem needs to support is
4 entries long (fault, pmd_fault, page_mkwrite, pfn_mkwrite), but the list of
functions in DAX to call is only 3 entries long (dax_iomap_fault(),
dax_iomap_pmd_fault(), dax_pfn_mkwrite())  This is probably because both
fault() and page_mkwrite() end up calling dax_iomap_fault().  Can you please
add a little text to make this clearer?

Yay for getting rid of the old buffer_head based DAX code!

Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
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