[RFC PATCH] fs: obtain the inode generation number from vfs directly

[Tavian Barnes]

On Tue, 27 Aug 2024 01:41:08 +0000, Hongbo Li wrote:
> Many mainstream file systems already support the GETVERSION ioctl,
> and their implementations are completely the same, essentially
> just obtain the value of i_generation. We think this ioctl can be
> implemented at the VFS layer, so the file systems do not need to
> implement it individually.
>
> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
> ---
>  fs/ioctl.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 64776891120c..dff887ec52c4 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -878,6 +878,9 @@ static int do_vfs_ioctl(struct file *filp, unsigned int fd,
>  	case FS_IOC_GETFSUUID:
>  		return ioctl_getfsuuid(filp, argp);
>  
> +	case FS_IOC_GETVERSION:
> +		return put_user(inode->i_generation, (int __user *)argp);
> +
>  	case FS_IOC_GETFSSYSFSPATH:
>  		return ioctl_get_fs_sysfs_path(filp, argp);
>  
> @@ -992,6 +995,9 @@ COMPAT_SYSCALL_DEFINE3(ioctl, unsigned int, fd, unsigned int, cmd,
>  		cmd = (cmd == FS_IOC32_GETFLAGS) ?
>  			FS_IOC_GETFLAGS : FS_IOC_SETFLAGS;
>  		fallthrough;

The above case falls through...

> +	case FS_IOC32_GETVERSION:
> +		cmd = FS_IOC_GETVERSION;

... to this new case, which clobbers cmd, breaking FS_IOC32_[GS]ETFLAGS.

> +		fallthrough;
>  	/*
>  	 * everything else in do_vfs_ioctl() takes either a compatible
>  	 * pointer argument or no argument -- call it with a modified