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Date: Mon, 5 Feb 2024 21:08:53 -0800
From: "Darrick J. Wong" <djwong@kernel.org>
To: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Randy Dunlap <rdunlap@infradead.org>, dsterba@suse.cz,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-ext4@vger.kernel.org, Christian Brauner <brauner@kernel.org>,
	Jan Kara <jack@suse.cz>, Dave Chinner <dchinner@redhat.com>,
	Theodore Ts'o <tytso@mit.edu>, Josef Bacik <josef@toxicpanda.com>
Subject: Re: [PATCH 4/6] fs: FS_IOC_GETSYSFSNAME
Message-ID: <20240206050853.GQ616564@frogsfrogsfrogs>
References: <20240205200529.546646-1-kent.overstreet@linux.dev>
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 <20240206013931.GK355@twin.jikos.cz>
 <ca885dd8-4ac1-43a9-9b0c-79b63cae0620@infradead.org>
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On Mon, Feb 05, 2024 at 11:33:11PM -0500, Kent Overstreet wrote:
> On Mon, Feb 05, 2024 at 08:20:10PM -0800, Randy Dunlap wrote:
> > 
> > 
> > On 2/5/24 17:39, David Sterba wrote:
> > > On Mon, Feb 05, 2024 at 05:43:37PM -0500, Kent Overstreet wrote:
> > >> On Mon, Feb 05, 2024 at 02:27:32PM -0800, Darrick J. Wong wrote:
> > >>> On Mon, Feb 05, 2024 at 03:05:15PM -0500, Kent Overstreet wrote:
> > >>>> @@ -231,6 +235,7 @@ struct fsxattr {
> > >>>>  #define FS_IOC_SETFSLABEL		_IOW(0x94, 50, char[FSLABEL_MAX])
> > >>>>  #define FS_IOC_GETFSUUID		_IOR(0x94, 51, struct fsuuid2)
> > >>>>  #define FS_IOC_SETFSUUID		_IOW(0x94, 52, struct fsuuid2)
> > >>>> +#define FS_IOC_GETFSSYSFSNAME		_IOR(0x94, 53, struct fssysfsname)
> > >>>
> > >>> 0x94 is btrfs, don't add things to their "name" space.
> > >>
> > >> Can we please document this somewhere!?
> > >>
> > >> What, dare I ask, is the "namespace" I should be using?
> > > 
> > > Grep for _IOCTL_MAGIC in include/uapi:
> > > 
> > > uapi/linux/aspeed-lpc-ctrl.h:#define __ASPEED_LPC_CTRL_IOCTL_MAGIC 0xb2
> > > uapi/linux/aspeed-p2a-ctrl.h:#define __ASPEED_P2A_CTRL_IOCTL_MAGIC 0xb3
> > > uapi/linux/bt-bmc.h:#define __BT_BMC_IOCTL_MAGIC        0xb1
> > > uapi/linux/btrfs.h:#define BTRFS_IOCTL_MAGIC 0x94
> > > uapi/linux/f2fs.h:#define F2FS_IOCTL_MAGIC              0xf5
> > > uapi/linux/ipmi_bmc.h:#define __IPMI_BMC_IOCTL_MAGIC        0xB1
> > > uapi/linux/pfrut.h:#define PFRUT_IOCTL_MAGIC 0xEE
> > > uapi/rdma/rdma_user_ioctl.h:#define IB_IOCTL_MAGIC RDMA_IOCTL_MAGIC
> > > uapi/rdma/rdma_user_ioctl_cmds.h:#define RDMA_IOCTL_MAGIC       0x1b
> > > 
> > > The label ioctls inherited the 0x94 namespace for backward
> > > compatibility but as already said, it's the private namespace of btrfs.
> > > 
> > 
> > or more generally, see Documentation/userspace-api/ioctl/ioctl-number.rst.
> > 
> > For 0x94, it says:
> > 
> > 0x94  all    fs/btrfs/ioctl.h                                        Btrfs filesystem
> >              and linux/fs.h                                          some lifted to vfs/generic
> 
> You guys keep giving the same info over and over again, instead of
> anything that would be actually helpful...
> 
> Does anyone know what the proper "namespace" is for new VFS level
> ioctls?
> 
> ...Anyone?

I propose you use 0x15 (NAK) and add it to the Documentation/ as the
official VFS ioctl namespace. ;)

--D