linux-kernel - Re: [PATCH 4/6] fs: FS_IOC

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Message-ID: <bhxmfqyqjkpjtxhyj2w2pnzbx2whnc2qurg2fcjpphuli2lyzc@bea4fzncsnhc>
Date: Tue, 6 Feb 2024 00:13:15 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: "Darrick J. Wong" <djwong@...nel.org>
Cc: Randy Dunlap <rdunlap@...radead.org>, dsterba@...e.cz, 
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-btrfs@...r.kernel.org, 
	linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Dave Chinner <dchinner@...hat.com>, 
	Theodore Ts'o <tytso@....edu>, Josef Bacik <josef@...icpanda.com>
Subject: Re: [PATCH 4/6] fs: FS_IOC_GETSYSFSNAME

On Mon, Feb 05, 2024 at 09:08:53PM -0800, Darrick J. Wong wrote:
> 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. ;)

Done!