From: John Groves <John@groves.net>
To: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: John Groves <jgroves@micron.com>,
Jonathan Corbet <corbet@lwn.net>,
Dan Williams <dan.j.williams@intel.com>,
Vishal Verma <vishal.l.verma@intel.com>,
Dave Jiang <dave.jiang@intel.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
Matthew Wilcox <willy@infradead.org>,
linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
nvdimm@lists.linux.dev, john@jagalactic.com,
Dave Chinner <david@fromorbit.com>,
Christoph Hellwig <hch@infradead.org>,
dave.hansen@linux.intel.com, gregory.price@memverge.com
Subject: Re: [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h
Date: Mon, 26 Feb 2024 12:04:05 -0600 [thread overview]
Message-ID: <4v6ug44nrtk2tqvio2teglsm4auhdvocgyyggtlwc3xkv7b6zw@ntw24jye7omz> (raw)
In-Reply-To: <20240226165639.000025c6@Huawei.com>
On 24/02/26 04:56PM, Jonathan Cameron wrote:
> On Mon, 26 Feb 2024 10:44:43 -0600
> John Groves <John@groves.net> wrote:
>
> > On 24/02/26 12:39PM, Jonathan Cameron wrote:
> > > On Fri, 23 Feb 2024 11:41:51 -0600
> > > John Groves <John@Groves.net> 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@groves.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,
> > > > + * 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
> > > Why 2?
> >
> > You catch everything!
> >
> > This limit is in place to avoid supporting somethign we're not testing. It
> > will probably be raised later.
> >
> > Currently user space doesn't support deleting files, which makes it easy
> > to ignore whether any clients have a stale view of metadata. If there is
> > no delete, there's actually no reason to have more than 1 extent.
> Then have 1. + a Comment on why it is 1.
Actually we test the 2 case. That seemed important to testing ioctl and
famfs_meta_to_dax_offset(). It just doesn't yet happen in the wild. Will
clarify with a comment.
> >
> > > > +
> > > > +enum extent_type {
> > > > + SIMPLE_DAX_EXTENT = 13,
> > >
> > > Comment on this would be good to have
> >
> > Done. Basically we anticipate there being other types of extents in the
> > future.
>
> I was more curious about the 13!
I think I was just being feisty that day. Will drop that...
>
> >
> > >
> > > > + INVALID_EXTENT_TYPE,
> > > > +};
> > > > +
> > > > +struct famfs_extent {
> > > > + __u64 offset;
> > > > + __u64 len;
> > > > +};
> > > > +
> > > > +enum famfs_file_type {
> > > > + FAMFS_REG,
> > > > + FAMFS_SUPERBLOCK,
> > > > + FAMFS_LOG,
> > > > +};
> > > > +
> > > > +/**
> > > > + * 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;
> > >
> > > These are going to be potentially varying in size depending on arch, compiler
> > > settings etc. Been a while, but I though best practice for uapi was always
> > > fixed size elements even though we lose the typing.
> >
> > I might not be following you fully here. User space is running the same
> > arch as kernel, so an enum can't be a different size, right? It could be
> > a different size on different arches, but this is just between user/kernel.
>
> I can't remember why, but this has bitten me in the past.
> Ah, should have known Daniel would have written something on it ;)
> https://www.kernel.org/doc/html/next/process/botching-up-ioctls.html
>
> It's the fun of need for compat ioctls with 32bit userspace on 64bit kernels.
>
> The alignment one is key as well. That bit me more than once due to
> 32bit x86 aligning 64 bit integers at 32 bits.
>
> We could just not support these cases but it's easy to get right so why
> bother with complexity of ruling them out.
Makes sense. Will do.
>
> >
> > I initially thought of XDR for on-media-format, which file systems need
> > to do with on-media structs (superblocks, logs, inodes, etc. etc.). But
> > this struct is not used in that way.
> >
> > In fact, famfs' on-media/in-memory metadata (superblock, log, log entries)
> > is only ever read read and written by user space - so it's the user space
> > code that needs XDR on-media-format handling.
> >
> > So to clarify - do you think those enums should be u32 or the like?
>
> Yes. As it's userspace, uint32_t maybe or __u32. I 'think'
> both are acceptable in uapi headers these days.
Roger that.
Thanks,
John
next prev parent reply other threads:[~2024-02-26 18:04 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-23 17:41 [RFC PATCH 00/20] Introduce the famfs shared-memory file system John Groves
2024-02-23 17:41 ` [RFC PATCH 01/20] famfs: Documentation John Groves
2024-02-23 17:41 ` [RFC PATCH 02/20] dev_dax_iomap: Add fs_dax_get() func to prepare dax for fs-dax usage John Groves
2024-02-26 12:05 ` Jonathan Cameron
2024-02-26 15:00 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 03/20] dev_dax_iomap: Move dax_pgoff_to_phys from device.c to bus.c since both need it now John Groves
2024-02-26 12:10 ` Jonathan Cameron
2024-02-26 15:13 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap John Groves
2024-02-26 12:21 ` Jonathan Cameron
2024-02-26 15:48 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 05/20] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax John Groves
2024-02-26 12:32 ` Jonathan Cameron
2024-02-26 16:09 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 06/20] dev_dax_iomap: Add CONFIG_DEV_DAX_IOMAP kernel build parameter John Groves
2024-02-26 12:34 ` Jonathan Cameron
2024-02-26 16:12 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 07/20] famfs: Add include/linux/famfs_ioctl.h John Groves
2024-02-24 1:39 ` Randy Dunlap
2024-02-24 2:23 ` John Groves
2024-02-24 3:27 ` Randy Dunlap
2024-02-24 23:32 ` John Groves
2024-02-24 23:40 ` Randy Dunlap
2024-02-26 12:39 ` Jonathan Cameron
2024-02-26 16:44 ` John Groves
2024-02-26 16:56 ` Jonathan Cameron
2024-02-26 18:04 ` John Groves [this message]
2024-02-23 17:41 ` [RFC PATCH 08/20] famfs: Add famfs_internal.h John Groves
2024-02-26 12:48 ` Jonathan Cameron
2024-02-26 17:35 ` John Groves
2024-02-27 10:28 ` Jonathan Cameron
2024-02-28 1:06 ` John Groves
2024-02-27 13:38 ` Christian Brauner
2024-02-27 14:12 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 09/20] famfs: Add super_operations John Groves
2024-02-26 12:51 ` Jonathan Cameron
2024-02-26 21:47 ` John Groves
2024-02-27 10:34 ` Jonathan Cameron
2024-02-27 17:48 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 10/20] famfs: famfs_open_device() & dax_holder_operations John Groves
2024-02-26 12:56 ` Jonathan Cameron
2024-02-26 22:22 ` John Groves
2024-02-27 13:39 ` Christian Brauner
2024-02-27 18:38 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 11/20] famfs: Add fs_context_operations John Groves
2024-02-26 13:20 ` Jonathan Cameron
2024-02-26 22:43 ` John Groves
2024-02-27 13:41 ` Christian Brauner
2024-02-28 0:59 ` John Groves
2024-02-28 1:49 ` Randy Dunlap
2024-02-28 8:17 ` Christian Brauner
2024-02-28 10:07 ` Christian Brauner
2024-02-28 12:01 ` Christian Brauner
2024-02-23 17:41 ` [RFC PATCH 12/20] famfs: Add inode_operations and file_system_type John Groves
2024-02-26 13:25 ` Jonathan Cameron
2024-02-26 22:53 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 13/20] famfs: Add iomap_ops John Groves
2024-02-26 13:30 ` Jonathan Cameron
2024-02-26 23:00 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 14/20] famfs: Add struct file_operations John Groves
2024-02-26 13:32 ` Jonathan Cameron
2024-02-26 23:09 ` John Groves
2024-02-23 17:41 ` [RFC PATCH 15/20] famfs: Add ioctl to file_operations John Groves
2024-02-26 13:44 ` Jonathan Cameron
2024-02-23 17:42 ` [RFC PATCH 16/20] famfs: Add fault counters John Groves
2024-02-23 18:23 ` Dave Hansen
2024-02-23 19:56 ` John Groves
2024-02-23 20:04 ` Dan Williams
2024-02-23 20:39 ` John Groves
2024-02-23 21:19 ` Dave Hansen
2024-02-23 23:50 ` Dan Williams
2024-02-24 3:59 ` Matthew Wilcox
2024-02-24 4:30 ` Dan Williams
2024-02-23 17:42 ` [RFC PATCH 17/20] famfs: Add module stuff John Groves
2024-02-26 13:47 ` Jonathan Cameron
2024-02-27 22:15 ` John Groves
2024-02-23 17:42 ` [RFC PATCH 18/20] famfs: Support character dax via the dev_dax_iomap patch John Groves
2024-02-26 13:52 ` Jonathan Cameron
2024-02-27 22:27 ` John Groves
2024-02-23 17:42 ` [RFC PATCH 19/20] famfs: Update MAINTAINERS file John Groves
2024-02-23 17:42 ` [RFC PATCH 20/20] famfs: Add Kconfig and Makefile plumbing John Groves
2024-02-24 1:50 ` Randy Dunlap
2024-02-24 2:24 ` John Groves
2024-02-24 0:07 ` [RFC PATCH 00/20] Introduce the famfs shared-memory file system Luis Chamberlain
2024-02-26 13:27 ` John Groves
2024-02-26 15:53 ` Luis Chamberlain
2024-02-26 21:16 ` John Groves
2024-02-27 0:58 ` Luis Chamberlain
2024-02-27 2:05 ` John Groves
2024-02-29 2:15 ` Dave Chinner
2024-02-29 14:52 ` John Groves
2024-03-11 1:29 ` Dave Chinner
2024-02-29 6:52 ` Amir Goldstein
2024-02-29 22:16 ` John Groves
2024-05-17 9:55 ` Miklos Szeredi
2024-05-19 5:59 ` Amir Goldstein
2024-05-22 2:05 ` John Groves
2024-05-22 8:58 ` Miklos Szeredi
2024-05-22 10:16 ` Amir Goldstein
2024-05-22 11:28 ` Miklos Szeredi
2024-05-22 13:41 ` Amir Goldstein
2024-05-23 2:49 ` John Groves
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