On Wed, 12 May 2010 15:49:49 -0600, Andreas Dilger <andreas.dilger@xxxxxxxxxx> wrote:
> On 2010-05-12, at 09:50, Aneesh Kumar K.V wrote:
> > +static long do_sys_name_to_handle(struct path *path,
> > + struct file_handle __user *ufh)
> > +{
> > + if (handle_size <= f_handle.handle_size) {
> > + /* get the uuid */
> > + retval = sb->s_op->get_fsid(sb, &this_fs_id);
> > + if (!retval) {
> > + /*
> > + * Now verify whether we get the same vfsmount
> > + * if we lookup with uuid. In case we end up having
> > + * same uuid for the multiple file systems. When doing
> > + * uuid based lookup we would return the first one.So
> > + * with name_to_handle if we don't find the same
> > + * vfsmount with lookup return EOPNOTSUPP
> > + */
> > + mnt = fs_get_vfsmount(current, &this_fs_id);
> > + if (mnt != path->mnt) {
> > + retval = -EOPNOTSUPP;
> > + mntput(mnt);
> > + goto err_free_out;
> > + }
>
> I don't see that this does anything for us except add overhead. This is no protection against mounting a second filesystem with the same UUID after the handle is returned, since there is no expiration for file handles.
>
> At best I think we could start by changing the list-based UUID lookup
> with a hash-based one, and when adding a duplicate UUID at mount time
> start by printing out an error message to the console in case of
> duplicated UUIDs, and maybe at some point in the future this might
> cause the mount to fail (though I don't think we can make that
> decision lightly or quickly).
I actually was looking at doing this. That is something in line of
register_for_handle_lookup(struct vfsmount *mnt);
Each file system will call this in their gets_sb callback after calling
get_sb_bdev. ie
static int ext4_get_sb(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data, struct vfsmount *mnt)
{
int retval;
retval = get_sb_bdev(fs_type, flags, dev_name, data,
ext4_fill_super,mnt);
if (register_for_handle_lookup(mnt)) {
printk(KERN_INFO, "File system won't be available or handle lookup");
}
return retval;
}
-aneesh
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