linux-kernel - Re: [RFC PATCH 13/20] famfs: Add iomap

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Date: Mon, 26 Feb 2024 17:00:00 -0600
From: John Groves <John@...ves.net>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: John Groves <jgroves@...ron.com>, Jonathan Corbet <corbet@....net>, 
	Dan Williams <dan.j.williams@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, 
	Dave Jiang <dave.jiang@...el.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Matthew Wilcox <willy@...radead.org>, 
	linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev, john@...alactic.com, 
	Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@...radead.org>, 
	dave.hansen@...ux.intel.com, gregory.price@...verge.com
Subject: Re: [RFC PATCH 13/20] famfs: Add iomap_ops

On 24/02/26 01:30PM, Jonathan Cameron wrote:
> On Fri, 23 Feb 2024 11:41:57 -0600
> John Groves <John@...ves.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@...ves.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)

Yessir.

> 
> 
> > +
> > +/**
> > + * 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_...

Done

> 
> > +}
> 
> 
> > +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()....

Done, thanks

John