Re: [RFC PATCH 13/20] famfs: Add iomap_ops

Jonathan Cameron
2024-02-26T13:30:41Z

On Fri, 23 Feb 2024 11:41:57 -0600
John Groves <John@Groves.net> wrote:

> This commit introduces the famfs iomap_ops. When either
> dax_iomap_fault() or dax_iomap_rw() is called, we get a callback
> via our iomap_begin() handler. The question being asked is
> "please resolve (file, offset) to (daxdev, offset)". The function
> famfs_meta_to_dax_offset() does this.
>
> The per-file metadata is just an extent list to the
> backing dax dev. The order of this resolution is O(N) for N
> extents. Note with the current user space, files usually have
> only one extent.
>
> Signed-off-by: John Groves <john@groves.net>

> ---
> fs/famfs/famfs_file.c | 245 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 245 insertions(+)
> create mode 100644 fs/famfs/famfs_file.c
>
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> new file mode 100644
> index 000000000000..fc667d5f7be8
> --- /dev/null
> +++ b/fs/famfs/famfs_file.c
> @@ -0,0 +1,245 @@

> +static int
> +famfs_meta_to_dax_offset(
> + struct inode *inode,
> + struct iomap *iomap,
> + loff_t offset,
> + loff_t len,
> + unsigned int flags)
> +{
> + struct famfs_file_meta *meta = (struct famfs_file_meta *)inode->i_private;

i_private is void * so no need for explicit cast (C spec says this is always fine without)

> +
> +/**
> + * famfs_iomap_begin()
> + *
> + * This function is pretty simple because files are
> + * * never partially allocated
> + * * never have holes (never sparse)
> + * * never "allocate on write"
> + */
> +static int
> +famfs_iomap_begin(
> + struct inode *inode,
> + loff_t offset,
> + loff_t length,
> + unsigned int flags,
> + struct iomap *iomap,
> + struct iomap *srcmap)
> +{
> + struct famfs_file_meta *meta = inode->i_private;
> + size_t size;
> + int rc;
> +
> + size = i_size_read(inode);
> +
> + WARN_ON(size != meta->file_size);
> +
> + rc = famfs_meta_to_dax_offset(inode, iomap, offset, length, flags);
> +
> + return rc;
return famfs_meta_...

> +}

> +static vm_fault_t
> +famfs_filemap_map_pages(
> + struct vm_fault *vmf,
> + pgoff_t start_pgoff,
> + pgoff_t end_pgoff)
> +{
> + vm_fault_t ret;
> +
> + ret = filemap_map_pages(vmf, start_pgoff, end_pgoff);
> + return ret;
return filename_map_pages()....

> +}
> +
>