Re: [PATCH 6/8] xfs: hoist unlinked list search and mapping to a separate function

[Brian Foster <bfoster@redhat.com>]

On Thu, Jan 31, 2019 at 03:18:27PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> There's a loop that searches an unlinked bucket list to find the inode
> that points to a given inode.  Hoist this into a separate function;
> later we'll use our iunlink backref cache to bypass the slow list
> operation.  No functional changes.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_inode.c |  136 ++++++++++++++++++++++++++++++++++++++--------------
>  1 file changed, 99 insertions(+), 37 deletions(-)
> 
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index ea38b66fbc59..d5b3f8fdac7e 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2084,6 +2084,100 @@ xfs_iunlink(
>  	return error;
>  }
>  
> +/* Return the imap, dinode pointer, and buffer for an inode. */
> +STATIC int
> +xfs_iunlink_map_ino(
> +	struct xfs_trans	*tp,
> +	xfs_ino_t		next_ino,

Might be good to clean up some of these variable names as this code gets
factored out. E.g., "next_ino" doesn't mean much more than "ino" in the
context of this helper.

> +	struct xfs_imap		*imap,
> +	struct xfs_dinode	**dipp,
> +	struct xfs_buf		**bpp)
> +{
> +	struct xfs_mount	*mp = tp->t_mountp;
> +	int			error;
> +
> +	imap->im_blkno = 0;
> +	error = xfs_imap(mp, tp, next_ino, imap, 0);
> +	if (error) {
> +		xfs_warn(mp, "%s: xfs_imap returned error %d.",
> +				__func__, error);
> +		return error;
> +	}
> +
> +	error = xfs_imap_to_bp(mp, tp, imap, dipp, bpp, 0, 0);
> +	if (error) {
> +		xfs_warn(mp, "%s: xfs_imap_to_bp returned error %d.",
> +				__func__, error);
> +		return error;
> +	}
> +
> +	return 0;
> +}
> +
> +/*
> + * Walk the unlinked chain from @head_agino until we find the inode that
> + * points to @target_ino.  Return the inode number, map, dinode pointer,
> + * and inode cluster buffer of that inode as @ino, @imap, @dipp, and @bpp.
> + *
> + * Do not call this function if @target_agino is the head of the list.
> + */
> +STATIC int
> +xfs_iunlink_map_prev(
> +	struct xfs_trans	*tp,
> +	struct xfs_perag	*pag,
> +	xfs_agino_t		head_agino,
> +	xfs_agino_t		target_agino,
> +	xfs_ino_t		*ino,
> +	struct xfs_imap		*imap,
> +	struct xfs_dinode	**dipp,
> +	struct xfs_buf		**bpp)
> +{

It would also be nice to have some oneline comments next to the params
of some of these functions.

> +	struct xfs_imap		last_imap;
> +	struct xfs_mount	*mp = tp->t_mountp;
> +	struct xfs_buf		*last_ibp = NULL;
> +	struct xfs_dinode	*last_dip;
> +	xfs_ino_t		next_ino = NULLFSINO;
> +	xfs_agino_t		next_agino;
> +	int			error;
> +
> +	ASSERT(head_agino != target_agino);
> +
> +	next_agino = head_agino;
> +	while (next_agino != target_agino) {
> +		xfs_agino_t	unlinked_agino;
> +
> +		if (last_ibp)
> +			xfs_trans_brelse(tp, last_ibp);
> +
> +		next_ino = XFS_AGINO_TO_INO(mp, pag->pag_agno, next_agino);
> +		error = xfs_iunlink_map_ino(tp, next_ino, &last_imap,
> +				&last_dip, &last_ibp);
> +		if (error)
> +			return error;
> +
> +		unlinked_agino = be32_to_cpu(last_dip->di_next_unlinked);
> +		if (!xfs_verify_agino(mp, pag->pag_agno, next_agino) ||

Should the next_agino above be unlinked_agino? Also is the == check
below a loop check (comment pls)?

> +		    next_agino == unlinked_agino) {
> +			XFS_CORRUPTION_ERROR(__func__,
> +					XFS_ERRLEVEL_LOW, mp,
> +					last_dip, sizeof(*last_dip));
> +			error = -EFSCORRUPTED;
> +			return error;
> +		}
> +		next_agino = unlinked_agino;
> +	}
> +
> +	/* Should never happen, but don't return garbage. */
> +	if (next_ino == NULLFSINO)
> +		return -EFSCORRUPTED;
> +
> +	*ino = next_ino;
> +	memcpy(imap, &last_imap, sizeof(last_imap));
> +	*dipp = last_dip;
> +	*bpp = last_ibp;
> +	return 0;
> +}
> +
>  /*
>   * Pull the on-disk inode from the AGI unlinked list.
>   */
> @@ -2153,43 +2247,11 @@ xfs_iunlink_remove(
>  	} else {
>  		struct xfs_imap	imap;
>  
> -		/*
> -		 * We need to search the list for the inode being freed.
> -		 */
> -		last_ibp = NULL;
> -		while (next_agino != agino) {
> -			if (last_ibp)
> -				xfs_trans_brelse(tp, last_ibp);
> -
> -			imap.im_blkno = 0;
> -			next_ino = XFS_AGINO_TO_INO(mp, agno, next_agino);
> -
> -			error = xfs_imap(mp, tp, next_ino, &imap, 0);
> -			if (error) {
> -				xfs_warn(mp,
> -	"%s: xfs_imap returned error %d.",
> -					 __func__, error);
> -				goto out_unlock;
> -			}
> -
> -			error = xfs_imap_to_bp(mp, tp, &imap, &last_dip,
> -					       &last_ibp, 0, 0);
> -			if (error) {
> -				xfs_warn(mp,
> -	"%s: xfs_imap_to_bp returned error %d.",
> -					__func__, error);
> -				goto out_unlock;
> -			}
> -
> -			next_agino = be32_to_cpu(last_dip->di_next_unlinked);
> -			if (!xfs_verify_agino(mp, agno, next_agino)) {
> -				XFS_CORRUPTION_ERROR(__func__,
> -						XFS_ERRLEVEL_LOW, mp,
> -						last_dip, sizeof(*last_dip));
> -				error = -EFSCORRUPTED;
> -				goto out_unlock;
> -			}
> -		}
> +		/* We need to search the list for the inode being freed. */
> +		error = xfs_iunlink_map_prev(tp, pag, next_agino, agino,
> +				&next_ino, &imap, &last_dip, &last_ibp);

Another variable nit... next_ino is kind of confusing here, particularly
where we still use next_agino as well. The former is actually the "prev"
ino output, right?

Brian

> +		if (error)
> +			goto out_unlock;
>  
>  		/*
>  		 * Now last_ibp points to the buffer previous to us on the
>