gfs2: hole_size improvement

Reimplement function hole_size based on a generic function for walking
the metadata tree and rename hole_size to gfs2_hole_size.  While
previously, multiple invocations of hole_size were sometimes needed to
walk across the entire hole, the new implementation always returns the
entire hole at once (provided that the caller is interested in the total
size).
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/bmap.c

@@ -278,6 +278,21 @@ static inline __be64 *metapointer(unsigned int height, const struct metapath *mp
 	return p + mp->mp_list[height];
 }
 
+static inline const __be64 *metaend(unsigned int height, const struct metapath *mp)
+{
+	const struct buffer_head *bh = mp->mp_bh[height];
+	return (const __be64 *)(bh->b_data + bh->b_size);
+}
+
+static void clone_metapath(struct metapath *clone, struct metapath *mp)
+{
+	unsigned int hgt;
+
+	*clone = *mp;
+	for (hgt = 0; hgt < mp->mp_aheight; hgt++)
+		get_bh(clone->mp_bh[hgt]);
+}
+
 static void gfs2_metapath_ra(struct gfs2_glock *gl, __be64 *start, __be64 *end)
 {
 	const __be64 *t;
@@ -419,6 +434,142 @@ static inline unsigned int gfs2_extent_length(void *start, unsigned int len, __b
 	return (ptr - first);
 }
 
+typedef const __be64 *(*gfs2_metadata_walker)(
+		struct metapath *mp,
+		const __be64 *start, const __be64 *end,
+		u64 factor, void *data);
+
+#define WALK_STOP ((__be64 *)0)
+#define WALK_NEXT ((__be64 *)1)
+
+static int gfs2_walk_metadata(struct inode *inode, sector_t lblock,
+		u64 len, struct metapath *mp, gfs2_metadata_walker walker,
+		void *data)
+{
+	struct metapath clone;
+	struct gfs2_inode *ip = GFS2_I(inode);
+	struct gfs2_sbd *sdp = GFS2_SB(inode);
+	const __be64 *start, *end, *ptr;
+	u64 factor = 1;
+	unsigned int hgt;
+	int ret = 0;
+
+	for (hgt = ip->i_height - 1; hgt >= mp->mp_aheight; hgt--)
+		factor *= sdp->sd_inptrs;
+
+	for (;;) {
+		u64 step;
+
+		/* Walk indirect block. */
+		start = metapointer(hgt, mp);
+		end = metaend(hgt, mp);
+
+		step = (end - start) * factor;
+		if (step > len)
+			end = start + DIV_ROUND_UP_ULL(len, factor);
+
+		ptr = walker(mp, start, end, factor, data);
+		if (ptr == WALK_STOP)
+			break;
+		if (step >= len)
+			break;
+		len -= step;
+		if (ptr != WALK_NEXT) {
+			BUG_ON(!*ptr);
+			mp->mp_list[hgt] += ptr - start;
+			goto fill_up_metapath;
+		}
+
+lower_metapath:
+		/* Decrease height of metapath. */
+		if (mp != &clone) {
+			clone_metapath(&clone, mp);
+			mp = &clone;
+		}
+		brelse(mp->mp_bh[hgt]);
+		mp->mp_bh[hgt] = NULL;
+		if (!hgt)
+			break;
+		hgt--;
+		factor *= sdp->sd_inptrs;
+
+		/* Advance in metadata tree. */
+		(mp->mp_list[hgt])++;
+		start = metapointer(hgt, mp);
+		end = metaend(hgt, mp);
+		if (start >= end) {
+			mp->mp_list[hgt] = 0;
+			if (!hgt)
+				break;
+			goto lower_metapath;
+		}
+
+fill_up_metapath:
+		/* Increase height of metapath. */
+		if (mp != &clone) {
+			clone_metapath(&clone, mp);
+			mp = &clone;
+		}
+		ret = fillup_metapath(ip, mp, ip->i_height - 1);
+		if (ret < 0)
+			break;
+		hgt += ret;
+		for (; ret; ret--)
+			do_div(factor, sdp->sd_inptrs);
+		mp->mp_aheight = hgt + 1;
+	}
+	if (mp == &clone)
+		release_metapath(mp);
+	return ret;
+}
+
+struct gfs2_hole_walker_args {
+	u64 blocks;
+};
+
+static const __be64 *gfs2_hole_walker(struct metapath *mp,
+		const __be64 *start, const __be64 *end,
+		u64 factor, void *data)
+{
+	struct gfs2_hole_walker_args *args = data;
+	const __be64 *ptr;
+
+	for (ptr = start; ptr < end; ptr++) {
+		if (*ptr) {
+			args->blocks += (ptr - start) * factor;
+			if (mp->mp_aheight == mp->mp_fheight)
+				return WALK_STOP;
+			return ptr;  /* increase height */
+		}
+	}
+	args->blocks += (end - start) * factor;
+	return WALK_NEXT;
+}
+
+/**
+ * gfs2_hole_size - figure out the size of a hole
+ * @inode: The inode
+ * @lblock: The logical starting block number
+ * @len: How far to look (in blocks)
+ * @mp: The metapath at lblock
+ * @iomap: The iomap to store the hole size in
+ *
+ * This function modifies @mp.
+ *
+ * Returns: errno on error
+ */
+static int gfs2_hole_size(struct inode *inode, sector_t lblock, u64 len,
+			  struct metapath *mp, struct iomap *iomap)
+{
+	struct gfs2_hole_walker_args args = { };
+	int ret = 0;
+
+	ret = gfs2_walk_metadata(inode, lblock, len, mp, gfs2_hole_walker, &args);
+	if (!ret)
+		iomap->length = args.blocks << inode->i_blkbits;
+	return ret;
+}
+
 static inline void bmap_lock(struct gfs2_inode *ip, int create)
 {
 	if (create)
@@ -615,62 +766,6 @@ static int gfs2_iomap_alloc(struct inode *inode, struct iomap *iomap,
 	return 0;
 }
 
-/**
- * hole_size - figure out the size of a hole
- * @inode: The inode
- * @lblock: The logical starting block number
- * @mp: The metapath
- *
- * Returns: The hole size in bytes
- *
- */
-static u64 hole_size(struct inode *inode, sector_t lblock, struct metapath *mp)
-{
-	struct gfs2_inode *ip = GFS2_I(inode);
-	struct gfs2_sbd *sdp = GFS2_SB(inode);
-	struct metapath mp_eof;
-	u64 factor = 1;
-	int hgt;
-	u64 holesz = 0;
-	const __be64 *first, *end, *ptr;
-	const struct buffer_head *bh;
-	u64 lblock_stop = (i_size_read(inode) - 1) >> inode->i_blkbits;
-	int zeroptrs;
-	bool done = false;
-
-	/* Get another metapath, to the very last byte */
-	find_metapath(sdp, lblock_stop, &mp_eof, ip->i_height);
-	for (hgt = ip->i_height - 1; hgt >= 0 && !done; hgt--) {
-		bh = mp->mp_bh[hgt];
-		if (bh) {
-			zeroptrs = 0;
-			first = metapointer(hgt, mp);
-			end = (const __be64 *)(bh->b_data + bh->b_size);
-
-			for (ptr = first; ptr < end; ptr++) {
-				if (*ptr) {
-					done = true;
-					break;
-				} else {
-					zeroptrs++;
-				}
-			}
-		} else {
-			zeroptrs = sdp->sd_inptrs;
-		}
-		if (factor * zeroptrs >= lblock_stop - lblock + 1) {
-			holesz = lblock_stop - lblock + 1;
-			break;
-		}
-		holesz += factor * zeroptrs;
-
-		factor *= sdp->sd_inptrs;
-		if (hgt && (mp->mp_list[hgt - 1] < mp_eof.mp_list[hgt - 1]))
-			(mp->mp_list[hgt - 1])++;
-	}
-	return holesz << inode->i_blkbits;
-}
-
 static void gfs2_stuffed_iomap(struct inode *inode, struct iomap *iomap)
 {
 	struct gfs2_inode *ip = GFS2_I(inode);
@@ -726,6 +821,7 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
 
 	lblock = pos >> inode->i_blkbits;
 	lend = (pos + length + sdp->sd_sb.sb_bsize - 1) >> inode->i_blkbits;
+	len = lend - lblock;
 
 	iomap->offset = lblock << inode->i_blkbits;
 	iomap->addr = IOMAP_NULL_ADDR;
@@ -780,7 +876,7 @@ int gfs2_iomap_begin(struct inode *inode, loff_t pos, loff_t length,
 		if (pos >= size)
 			ret = -ENOENT;
 		else if (height <= ip->i_height)
-			iomap->length = hole_size(inode, lblock, &mp);
+			ret = gfs2_hole_size(inode, lblock, len, &mp, iomap);
 		else
 			iomap->length = size - pos;
 	}