xfs: cleanup xfs_growfs_compute_deltas

xfs_growfs_compute_deltas has an odd calling conventions, and looks
very convoluted due to the use of do_div and strangely named and typed
variables.

Rename it, make it return the agcount and let the caller calculate the
delta.  The internally use the better div_u64_rem helper and descriptive
variable names and types.  Also add a comment describing what the
function is used for.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

3 files changed, 26 insertions, 27 deletions

diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
index 0c5f0548021f..6cab66781d66 100644
--- a/fs/xfs/libxfs/xfs_ag.c
+++ b/fs/xfs/libxfs/xfs_ag.c
@@ -863,32 +863,30 @@ resv_err:
 	return err2;
 }
 
-void
-xfs_growfs_compute_deltas(
+/*
+ * Return the agcount for the new file system size passed in *nb and adjust *nb
+ * when it has to be reduced because of maximum AG count or because it would
+ * create a below minimum size AG.
+ */
+xfs_agnumber_t
+xfs_growfs_compute_agcount(
 	struct xfs_mount	*mp,
-	xfs_rfsblock_t		*nb,
-	int64_t			*deltap,
-	xfs_agnumber_t		*nagcountp)
+	xfs_rfsblock_t		*nb)
 {
-	xfs_rfsblock_t	nb_div, nb_mod;
-	int64_t		delta;
-	xfs_agnumber_t	nagcount;
-
-	nb_div = *nb;
-	nb_mod = do_div(nb_div, mp->m_sb.sb_agblocks);
-	if (nb_mod && nb_mod >= XFS_MIN_AG_BLOCKS)
-		nb_div++;
-	else if (nb_mod)
-		*nb = nb_div * mp->m_sb.sb_agblocks;
-
-	if (nb_div > XFS_MAX_AGNUMBER + 1) {
-		nb_div = XFS_MAX_AGNUMBER + 1;
-		*nb = nb_div * mp->m_sb.sb_agblocks;
+	uint64_t		agcount; /* 64-bits wide to catch overflows */
+	xfs_extlen_t		remainder;
+
+	agcount = div_u64_rem(*nb, mp->m_sb.sb_agblocks, &remainder);
+	if (agcount >= XFS_MAX_AGNUMBER + 1) {
+		agcount = XFS_MAX_AGNUMBER + 1;
+		remainder = 0;
+	}
+	*nb = (xfs_rfsblock_t)agcount * mp->m_sb.sb_agblocks;
+	if (remainder >= XFS_MIN_AG_BLOCKS) {
+		*nb += remainder;
+		agcount++;
 	}
-	nagcount = nb_div;
-	delta = *nb - mp->m_sb.sb_dblocks;
-	*deltap = delta;
-	*nagcountp = nagcount;
+	return agcount;
 }
 
 /*
diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h
index 8aa4266c5571..fd22fe598931 100644
--- a/fs/xfs/libxfs/xfs_ag.h
+++ b/fs/xfs/libxfs/xfs_ag.h
@@ -329,12 +329,11 @@ struct aghdr_init_data {
 int xfs_ag_init_headers(struct xfs_mount *mp, struct aghdr_init_data *id);
 int xfs_ag_shrink_space(struct xfs_perag *pag, struct xfs_trans **tpp,
 			xfs_extlen_t delta);
-void
-xfs_growfs_compute_deltas(struct xfs_mount *mp, xfs_rfsblock_t *nb,
-			int64_t *deltap, xfs_agnumber_t *nagcountp);
 int xfs_ag_extend_space(struct xfs_perag *pag, struct xfs_trans *tp,
 			xfs_extlen_t len);
 int xfs_ag_get_geometry(struct xfs_perag *pag, struct xfs_ag_geometry *ageo);
+xfs_agnumber_t xfs_growfs_compute_agcount(struct xfs_mount *mp,
+		xfs_rfsblock_t *nb);
 
 static inline xfs_fsblock_t
 xfs_agbno_to_fsb(
diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 436857356a0a..67624a804a7f 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -124,7 +124,9 @@ xfs_growfs_data_private(
 			mp->m_sb.sb_rextsize);
 	if (error)
 		return error;
-	xfs_growfs_compute_deltas(mp, &nb, &delta, &nagcount);
+
+	nagcount = xfs_growfs_compute_agcount(mp, &nb);
+	delta = nb - mp->m_sb.sb_dblocks;
 
 	/*
 	 * Reject filesystems with a single AG because they are not