Re: [PATCH] Add MOUNT_STATUS ioctl to cdrom device

[Samphan Raruenrom <samphan@nectec.or.th>]

Christoph Hellwig wrote:
>>+	case CDROM_MOUNT_STATUS: {
>>+		struct super_block *sb = get_super(dev);
>>+		if (sb == NULL) return -EINVAL;
>>+		down_read(&current->namespace->sem);
>>+		struct vfsmount *mnt = NULL;
>>+		struct list_head *p;
>>+		list_for_each(p, &current->namespace->list) {
>>+			struct vfsmount *m = list_entry(p, struct vfsmount, mnt_list);
>>+			if (sb == m->mnt_sb) {
>>+				mnt = m; break;
>>+			}
>>+		}
>>+		up_read(&current->namespace->sem);		
>>+		drop_super(sb);		
>>+		int mstat = 0; /* 0 not mounted, 1 umount ok, 2 umount EBUSY */
>>+		if (mnt) mstat = 1 + (atomic_read(&mnt->mnt_count) > 1);
>>+		cdinfo(CD_DO_IOCTL, "mount status(%s) = %d\n", mnt->mnt_devname, mstat);
>>+		return mstat;
> WTF?  This is not only a layering violation but also totally racy.

I'm sorry for issueing this layering violation. I read a guideline that
it's easier to submit a patch to add device driver ioctl than inventing
something new. It really doesn't belong here.
Could you guide me where else can I place this functionality?

(my random idea)
- fcntl(open("/dev/cdrom", F_MNTSTAT)
- umount2("/dev/cdrom", MS_TEST) // not actually perform
- new system call! e.g. mntstat(open("/dev/cdrom"))

-- 
Samphan Raruenrom,
The Open Source Project,
National Electronics and Computer Technology Center,
National Science and Technology Development Agency,
Thailand.