On Tue, Feb 06, 2024 at 09:17:58AM +1100, Dave Chinner wrote:
> On Mon, Feb 05, 2024 at 03:05:13PM -0500, Kent Overstreet wrote:
> > Add a new generic ioctls for querying the filesystem UUID.
> >
> > These are lifted versions of the ext4 ioctls, with one change: we're not
> > using a flexible array member, because UUIDs will never be more than 16
> > bytes.
> >
> > This patch adds a generic implementation of FS_IOC_GETFSUUID, which
> > reads from super_block->s_uuid; FS_IOC_SETFSUUID is left for individual
> > filesystems to implement.
> >
> > Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > Cc: Christian Brauner <brauner@xxxxxxxxxx>
> > Cc: Jan Kara <jack@xxxxxxx>
> > Cc: Dave Chinner <dchinner@xxxxxxxxxx>
> > Cc: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> > Cc: Theodore Ts'o <tytso@xxxxxxx>
> > Cc: linux-fsdevel@xxxxxxxxxxxxxx
> > Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> > ---
> > fs/ioctl.c | 16 ++++++++++++++++
> > include/uapi/linux/fs.h | 16 ++++++++++++++++
> > 2 files changed, 32 insertions(+)
> >
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 76cf22ac97d7..858801060408 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -763,6 +763,19 @@ static int ioctl_fssetxattr(struct file *file, void __user *argp)
> > return err;
> > }
> >
> > +static int ioctl_getfsuuid(struct file *file, void __user *argp)
> > +{
> > + struct super_block *sb = file_inode(file)->i_sb;
> > +
> > + if (WARN_ON(sb->s_uuid_len > sizeof(sb->s_uuid)))
> > + sb->s_uuid_len = sizeof(sb->s_uuid);
>
> A "get"/read only ioctl should not be change superblock fields -
> this is not the place for enforcing superblock filed constraints.
> Make a helper function super_set_uuid(sb, uuid, uuid_len) for the
> filesystems to call that does all the validity checking and then
> sets the superblock fields appropriately.
*nod* good thought...
> > +struct fsuuid2 {
> > + __u32 fsu_len;
> > + __u32 fsu_flags;
> > + __u8 fsu_uuid[16];
> > +};
>
> Nobody in userspace will care that this is "version 2" of the ext4
> ioctl. I'd just name it "fs_uuid" as though the ext4 version didn't
> ever exist.
I considered that - but I decided I wanted the explicit versioning,
because too often we live with unfixed mistakes because versioning is
ugly, or something?
Doing a new revision of an API should be a normal, frequent thing, and I
want to start making it a convention.
>
> > +
> > /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
> > #define FILE_DEDUPE_RANGE_SAME 0
> > #define FILE_DEDUPE_RANGE_DIFFERS 1
> > @@ -215,6 +229,8 @@ struct fsxattr {
> > #define FS_IOC_FSSETXATTR _IOW('X', 32, struct fsxattr)
> > #define FS_IOC_GETFSLABEL _IOR(0x94, 49, char[FSLABEL_MAX])
> > #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)
>
> 0x94 is the btrfs ioctl space, not the VFS space - why did you
> choose that? That said, what is the VFS ioctl space identifier? 'v',
> perhaps?
"Promoting ioctls from fs to vfs without revising and renaming
considered harmful"... this is a mess that could have been avoided if we
weren't taking the lazy route.
And 'v' doesn't look like it to me, I really have no idea what to use
here. Does anyone?
