linux-ext4 - Re: [PATCH 4/6] fs: FS_IOC

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Date: Mon, 5 Feb 2024 20:20:10 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: dsterba@...e.cz, Kent Overstreet <kent.overstreet@...ux.dev>
Cc: "Darrick J. Wong" <djwong@...nel.org>, 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 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

-- 
#Randy