linux-kernel - Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs

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Date: Fri, 23 Feb 2024 20:23:21 -0600
From: John Groves <John@...ves.net>
To: Randy Dunlap <rdunlap@...radead.org>
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 07/20] famfs: Add include/linux/famfs_ioctl.h

On 24/02/23 05:39PM, Randy Dunlap wrote:
> Hi--
> 
> On 2/23/24 09:41, John Groves wrote:
> > Add uapi include file for famfs. The famfs user space uses ioctl on
> > individual files to pass in mapping information and file size. This
> > would be hard to do via sysfs or other means, since it's
> > file-specific.
> > 
> > Signed-off-by: John Groves <john@...ves.net>
> > ---
> >  include/uapi/linux/famfs_ioctl.h | 56 ++++++++++++++++++++++++++++++++
> >  1 file changed, 56 insertions(+)
> >  create mode 100644 include/uapi/linux/famfs_ioctl.h
> > 
> > diff --git a/include/uapi/linux/famfs_ioctl.h b/include/uapi/linux/famfs_ioctl.h
> > new file mode 100644
> > index 000000000000..6b3e6452d02f
> > --- /dev/null
> > +++ b/include/uapi/linux/famfs_ioctl.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2024 Micron Technology, Inc.
> > + *
> > + * This file system, originally based on ramfs the dax support from xfs,
> 
>       This is confusing to me. Is it just me? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Thanks Randy. I think I was trying to say "based on ramfs *plus* the dax
support from xfs. But I'll try to come up with something more clear than
that...

> 
> > + * is intended to allow multiple host systems to mount a common file system
> > + * view of dax files that map to shared memory.
> > + */
> > +#ifndef FAMFS_IOCTL_H
> > +#define FAMFS_IOCTL_H
> > +
> > +#include <linux/ioctl.h>
> > +#include <linux/uuid.h>
> > +
> > +#define FAMFS_MAX_EXTENTS 2
> > +
> > +enum extent_type {
> > +	SIMPLE_DAX_EXTENT = 13,
> > +	INVALID_EXTENT_TYPE,
> > +};
> > +
> > +struct famfs_extent {
> > +	__u64              offset;
> > +	__u64              len;
> > +};
> > +
> > +enum famfs_file_type {
> > +	FAMFS_REG,
> > +	FAMFS_SUPERBLOCK,
> > +	FAMFS_LOG,
> > +};
> > +
> > +/**
> 
> "/**" is used to begin kernel-doc comments, but this comment block is missing
> a few entries to make it be kernel-doc compatible. Please either add them
> or just use "/*" to begin the comment.

Will do, thanks. And I'll check the whole code base for other instances;
I won't be surprise if I was sloop about that in more than one place.

> 
> > + * struct famfs_ioc_map
> > + *
> > + * This is the metadata that indicates where the memory is for a famfs file
> > + */
> > +struct famfs_ioc_map {
> > +	enum extent_type          extent_type;
> > +	enum famfs_file_type      file_type;
> > +	__u64                     file_size;
> > +	__u64                     ext_list_count;
> > +	struct famfs_extent       ext_list[FAMFS_MAX_EXTENTS];
> > +};
> > +
> > +#define FAMFSIOC_MAGIC 'u'
> 
> This 'u' value should be documented in
> Documentation/userspace-api/ioctl/ioctl-number.rst.
> 
> and if possible, you might want to use values like 0x5x or 0x8x
> that don't conflict with the ioctl numbers that are already used
> in the 'u' space.

Will do. I was trying to be too clever there, invoking "mu" for
micron. 

> 
> > +
> > +/* famfs file ioctl opcodes */
> > +#define FAMFSIOC_MAP_CREATE    _IOW(FAMFSIOC_MAGIC, 1, struct famfs_ioc_map)
> > +#define FAMFSIOC_MAP_GET       _IOR(FAMFSIOC_MAGIC, 2, struct famfs_ioc_map)
> > +#define FAMFSIOC_MAP_GETEXT    _IOR(FAMFSIOC_MAGIC, 3, struct famfs_extent)
> > +#define FAMFSIOC_NOP           _IO(FAMFSIOC_MAGIC,  4)
> > +
> > +#endif /* FAMFS_IOCTL_H */
> 
> -- 
> #Randy

Thank you for taking the time to look it over, Randy.

John