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:
> > Add a new ioctl for getting the sysfs name of a filesystem - the path
> > under /sys/fs.
> >
> > This is going to let us standardize exporting data from sysfs across
> > filesystems, e.g. time stats.
> >
> > The returned path will always be of the form "$FSTYP/$SYSFS_IDENTIFIER",
> > where the sysfs identifier may be a UUID (for bcachefs) or a device name
> > (xfs).
> >
> > 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: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > ---
> > fs/ioctl.c | 17 +++++++++++++++++
> > include/linux/fs.h | 1 +
> > include/uapi/linux/fs.h | 5 +++++
> > 3 files changed, 23 insertions(+)
> >
> > diff --git a/fs/ioctl.c b/fs/ioctl.c
> > index 858801060408..cb3690811d3d 100644
> > --- a/fs/ioctl.c
> > +++ b/fs/ioctl.c
> > @@ -776,6 +776,20 @@ static int ioctl_getfsuuid(struct file *file, void __user *argp)
> > return copy_to_user(argp, &u, sizeof(u)) ? -EFAULT : 0;
> > }
> >
> > +static int ioctl_getfssysfsname(struct file *file, void __user *argp)
>
> ackpthspacesplease.
>
> "ioctl_get_fs_sysfs_name"?
It did feel a bit trolling writing that :)
>
> > +{
> > + struct super_block *sb = file_inode(file)->i_sb;
> > +
> > + if (!strlen(sb->s_sysfs_name))
> > + return -ENOIOCTLCMD;
> > +
> > + struct fssysfsname u = {};
> > +
> > + snprintf(u.name, sizeof(u.name), "%s/%s", sb->s_type->name, sb->s_sysfs_name);
>
> Does this actually guarantee that there will be a trailing null in the
> output? It's really stupid that GETFSLABEL can return an unterminated
> string if the label is exactly the size of the char array.
It's snprintf, so yes.
(queue another "why are we using raw char arrays everywhere in 2024"
rant, I have to double check this stuff too).
>
> > +
> > + return copy_to_user(argp, &u, sizeof(u)) ? -EFAULT : 0;
> > +}
> > +
> > /*
> > * do_vfs_ioctl() is not for drivers and not intended to be EXPORT_SYMBOL()'d.
> > * It's just a simple helper for sys_ioctl and compat_sys_ioctl.
> > @@ -861,6 +875,9 @@ static int do_vfs_ioctl(struct file *filp, unsigned int fd,
> > case FS_IOC_GETFSUUID:
> > return ioctl_getfsuuid(filp, argp);
> >
> > + case FS_IOC_GETFSSYSFSNAME:
>
> File System Ioctl Get File System System File System Name.
>
> Yuck.
>
> FS_IOC_GETSYSFSPATH?
>
> Also, do we want to establish that this works for /sys/fs and
> /sys/kernel/debug at the same time?
Yeah, I'll add a comment to that effect.
>
> > + return ioctl_getfssysfsname(filp, argp);
> > +
> > default:
> > if (S_ISREG(inode->i_mode))
> > return file_ioctl(filp, cmd, argp);
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index ff41ea6c3a9c..7f23f593f17c 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1258,6 +1258,7 @@ struct super_block {
> > char s_id[32]; /* Informational name */
> > uuid_t s_uuid; /* UUID */
> > u8 s_uuid_len; /* Default 16, possibly smaller for weird filesystems */
> > + char s_sysfs_name[UUID_STRING_LEN + 1];
> >
> > unsigned int s_max_links;
> >
> > diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> > index 0389fea87db5..6dd14a453277 100644
> > --- a/include/uapi/linux/fs.h
> > +++ b/include/uapi/linux/fs.h
> > @@ -78,6 +78,10 @@ struct fsuuid2 {
> > __u8 fsu_uuid[16];
> > };
> >
> > +struct fssysfsname {
> > + __u8 name[64];
> > +};
> > +
> > /* extent-same (dedupe) ioctls; these MUST match the btrfs ioctl definitions */
> > #define FILE_DEDUPE_RANGE_SAME 0
> > #define FILE_DEDUPE_RANGE_DIFFERS 1
> > @@ -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?
