Re: [PATCH] ceph: convert to generic_file_llseek

["Luís Henriques" <lhenriques@suse.de>]

Jeff Layton <jlayton@kernel.org> writes:

> There's no reason we need to lock the inode for write in order to handle
> an llseek. I suspect this should have been dropped in 2013 when we
> stopped doing vmtruncate in llseek.
>
> With that gone, ceph_llseek is functionally equivalent to
> generic_file_llseek, so just call that after getting the size.
>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/ceph/file.c | 52 +++++---------------------------------------------
>  1 file changed, 5 insertions(+), 47 deletions(-)
>

Nice!  I started reviewing your previous patch, and while checking other
filesystems I wondered if the generic_* could be used instead.  And here
it is.  And it may even fix races in the SEEK_CUR by locking f_lock.

Reviewed-by: Luís Henriques <lhenriques@suse.de>

Cheers,
-- 
Luís

> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index 0c13a3f23c99..0e82a1c383ca 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1989,57 +1989,15 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   */
>  static loff_t ceph_llseek(struct file *file, loff_t offset, int whence)
>  {
> -	struct inode *inode = file->f_mapping->host;
> -	struct ceph_fs_client *fsc = ceph_inode_to_client(inode);
> -	loff_t i_size;
> -	loff_t ret;
> -
> -	inode_lock(inode);
> -
>  	if (whence == SEEK_END || whence == SEEK_DATA || whence == SEEK_HOLE) {
> +		struct inode *inode = file_inode(file);
> +		int ret;
> +
>  		ret = ceph_do_getattr(inode, CEPH_STAT_CAP_SIZE, false);
>  		if (ret < 0)
> -			goto out;
> -	}
> -
> -	i_size = i_size_read(inode);
> -	switch (whence) {
> -	case SEEK_END:
> -		offset += i_size;
> -		break;
> -	case SEEK_CUR:
> -		/*
> -		 * Here we special-case the lseek(fd, 0, SEEK_CUR)
> -		 * position-querying operation.  Avoid rewriting the "same"
> -		 * f_pos value back to the file because a concurrent read(),
> -		 * write() or lseek() might have altered it
> -		 */
> -		if (offset == 0) {
> -			ret = file->f_pos;
> -			goto out;
> -		}
> -		offset += file->f_pos;
> -		break;
> -	case SEEK_DATA:
> -		if (offset < 0 || offset >= i_size) {
> -			ret = -ENXIO;
> -			goto out;
> -		}
> -		break;
> -	case SEEK_HOLE:
> -		if (offset < 0 || offset >= i_size) {
> -			ret = -ENXIO;
> -			goto out;
> -		}
> -		offset = i_size;
> -		break;
> +			return ret;
>  	}
> -
> -	ret = vfs_setpos(file, offset, max(i_size, fsc->max_file_size));
> -
> -out:
> -	inode_unlock(inode);
> -	return ret;
> +	return generic_file_llseek(file, offset, whence);
>  }
>  
>  static inline void ceph_zero_partial_page(
> -- 
>
> 2.36.1
>