Re: [PATCH v8 06/19] block, fs: Propagate write hints to the block device inode

[Bart Van Assche <bvanassche@acm.org>]

On 1/18/24 10:51, Kanchan Joshi wrote:
> Are you considering to change this so that hint is set only on one inode
> (and not on two)?
> IOW, should not this fragment be like below:
> 
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -306,7 +306,6 @@ static long fcntl_get_rw_hint(struct file *file,
> unsigned int cmd,
>    static long fcntl_set_rw_hint(struct file *file, unsigned int cmd,
>                                 unsigned long arg)
>    {
> -       void (*apply_whint)(struct file *, enum rw_hint);
>           struct inode *inode = file_inode(file);
>           u64 __user *argp = (u64 __user *)arg;
>           u64 hint;
> @@ -316,11 +315,15 @@ static long fcntl_set_rw_hint(struct file *file,
> unsigned int cmd,
>           if (!rw_hint_valid(hint))
>                   return -EINVAL;
> 
> +       /*
> +        * file->f_mapping->host may differ from inode. As an example
> +        * blkdev_open() modifies file->f_mapping
> +        */
> +       if (file->f_mapping->host != inode)
> +               inode = file->f_mapping->host;
> +
>           inode_lock(inode);
>           inode->i_write_hint = hint;
> -       apply_whint = inode->i_fop->apply_whint;
> -       if (apply_whint)
> -               apply_whint(file, hint);
>           inode_unlock(inode);

I think the above proposal would introduce a bug: it would break the
F_GET_RW_HINT implementation.

Thanks,

Bart.