fs: remove fs.f_write_hint

The value is now completely unused except for reporting it back through
the F_GET_FILE_RW_HINT ioctl, so remove the value and the two ioctls
for it.

Trying to use the F_SET_FILE_RW_HINT and F_GET_FILE_RW_HINT fcntls will
now return EINVAL, just like it would on a kernel that never supported
this functionality in the first place.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220308060529.736277-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

fs/fcntl.c

@@ -291,22 +291,6 @@ static long fcntl_rw_hint(struct file *file, unsigned int cmd,
 	u64 h;
 
 	switch (cmd) {
-	case F_GET_FILE_RW_HINT:
-		h = file_write_hint(file);
-		if (copy_to_user(argp, &h, sizeof(*argp)))
-			return -EFAULT;
-		return 0;
-	case F_SET_FILE_RW_HINT:
-		if (copy_from_user(&h, argp, sizeof(h)))
-			return -EFAULT;
-		hint = (enum rw_hint) h;
-		if (!rw_hint_valid(hint))
-			return -EINVAL;
-
-		spin_lock(&file->f_lock);
-		file->f_write_hint = hint;
-		spin_unlock(&file->f_lock);
-		return 0;
 	case F_GET_RW_HINT:
 		h = inode->i_write_hint;
 		if (copy_to_user(argp, &h, sizeof(*argp)))
@@ -431,8 +415,6 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
 		break;
 	case F_GET_RW_HINT:
 	case F_SET_RW_HINT:
-	case F_GET_FILE_RW_HINT:
-	case F_SET_FILE_RW_HINT:
 		err = fcntl_rw_hint(filp, cmd, arg);
 		break;
 	default:

fs/open.c

@@ -835,7 +835,6 @@ static int do_dentry_open(struct file *f,
 	     likely(f->f_op->write || f->f_op->write_iter))
 		f->f_mode |= FMODE_CAN_WRITE;
 
-	f->f_write_hint = WRITE_LIFE_NOT_SET;
 	f->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 
 	file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);

include/linux/fs.h

@@ -966,7 +966,6 @@ struct file {
 	 * Must not be taken from IRQ context.
 	 */
 	spinlock_t		f_lock;
-	enum rw_hint		f_write_hint;
 	atomic_long_t		f_count;
 	unsigned int 		f_flags;
 	fmode_t			f_mode;
@@ -2214,14 +2213,6 @@ static inline bool HAS_UNMAPPED_ID(struct user_namespace *mnt_userns,
 	       !gid_valid(i_gid_into_mnt(mnt_userns, inode));
 }
 
-static inline enum rw_hint file_write_hint(struct file *file)
-{
-	if (file->f_write_hint != WRITE_LIFE_NOT_SET)
-		return file->f_write_hint;
-
-	return file_inode(file)->i_write_hint;
-}
-
 static inline int iocb_flags(struct file *file);
 
 static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)