lib/printbuf: Tabstop improvements

 - Add a flag, has_indent_or_tabstops, that is set if indent level or
   tabstops are set.

 - Tabstops can no longer be set by modifying the tabstop array
   directly: instead, the new functions are provided:

   printbuf_tabstop_push()	- add a new tabstop, n spaces after
				  previous tabstop
   printbuf_tabtstop_pop()	- remove previous tabstop
   printbuf_tabstops_reset()	- remove all tabstops

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

8 files changed, 121 insertions, 49 deletions

diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c
index 938740544469..448a3ee27038 100644
--- a/fs/bcachefs/debug.c
+++ b/fs/bcachefs/debug.c
@@ -409,7 +409,8 @@ static const struct file_operations bfloat_failed_debug_ops = {
 static void bch2_cached_btree_node_to_text(struct printbuf *out, struct bch_fs *c,
 					   struct btree *b)
 {
-	out->tabstops[0] = 32;
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 32);
 
 	prt_printf(out, "%px btree=%s l=%u ",
 	       b,
diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
index d77092aa069e..3f1cf1ac921a 100644
--- a/fs/bcachefs/journal.c
+++ b/fs/bcachefs/journal.c
@@ -1255,8 +1255,9 @@ void __bch2_journal_debug_to_text(struct printbuf *out, struct journal *j)
 	u64 seq;
 	unsigned i;
 
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 24);
 	out->atomic++;
-	out->tabstops[0] = 24;
 
 	rcu_read_lock();
 	s = READ_ONCE(j->reservations);
diff --git a/fs/bcachefs/rebalance.c b/fs/bcachefs/rebalance.c
index ecc64dd92b05..17b289b051f2 100644
--- a/fs/bcachefs/rebalance.c
+++ b/fs/bcachefs/rebalance.c
@@ -268,7 +268,8 @@ void bch2_rebalance_work_to_text(struct printbuf *out, struct bch_fs *c)
 	struct bch_fs_rebalance *r = &c->rebalance;
 	struct rebalance_work w = rebalance_work(c);
 
-	out->tabstops[0] = 20;
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 20);
 
 	prt_printf(out, "fullest_dev (%i):", w.dev_most_full_idx);
 	prt_tab(out);
diff --git a/fs/bcachefs/super-io.c b/fs/bcachefs/super-io.c
index 3dacb8ffbe56..414c40cf3614 100644
--- a/fs/bcachefs/super-io.c
+++ b/fs/bcachefs/super-io.c
@@ -1425,8 +1425,8 @@ void bch2_sb_field_to_text(struct printbuf *out, struct bch_sb *sb,
 	const struct bch_sb_field_ops *ops = type < BCH_SB_FIELD_NR
 		? bch2_sb_field_ops[type] : NULL;
 
-	if (!out->tabstops[0])
-		out->tabstops[0] = 32;
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 32);
 
 	if (ops)
 		prt_printf(out, "%s", bch2_sb_fields[type]);
@@ -1474,8 +1474,8 @@ void bch2_sb_to_text(struct printbuf *out, struct bch_sb *sb,
 	u64 fields_have = 0;
 	unsigned nr_devices = 0;
 
-	if (!out->tabstops[0])
-		out->tabstops[0] = 32;
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 32);
 
 	mi = bch2_sb_get_members(sb);
 	if (mi) {
diff --git a/fs/bcachefs/sysfs.c b/fs/bcachefs/sysfs.c
index 2c650055f530..2dfed1ffadd7 100644
--- a/fs/bcachefs/sysfs.c
+++ b/fs/bcachefs/sysfs.c
@@ -560,7 +560,8 @@ SHOW(bch2_fs_counters)
 	u64 counter = 0;
 	u64 counter_since_mount = 0;
 
-	out->tabstops[0] = 32;
+	printbuf_tabstop_push(out, 32);
+
 	#define x(t, ...) \
 		if (attr == &sysfs_##t) {					\
 			counter             = percpu_u64_get(&c->counters[BCH_COUNTER_##t]);\
diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c
index ee2c7d9e7050..2f7d73170f35 100644
--- a/fs/bcachefs/util.c
+++ b/fs/bcachefs/util.c
@@ -526,7 +526,8 @@ void bch2_pd_controller_init(struct bch_pd_controller *pd)
 
 void bch2_pd_controller_debug_to_text(struct printbuf *out, struct bch_pd_controller *pd)
 {
-	out->tabstops[0] = 20;
+	if (!out->nr_tabstops)
+		printbuf_tabstop_push(out, 20);
 
 	prt_printf(out, "rate:");
 	prt_tab(out);
diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h
index eb2edb86b22c..24e62e56d18c 100644
--- a/include/linux/printbuf.h
+++ b/include/linux/printbuf.h
@@ -71,6 +71,8 @@ enum printbuf_si {
 	PRINTBUF_UNITS_10,	/* use powers of 10^3 (standard SI) */
 };
 
+#define PRINTBUF_INLINE_TABSTOPS	4
+
 struct printbuf {
 	char			*buf;
 	unsigned		size;
@@ -86,19 +88,33 @@ struct printbuf {
 	bool			heap_allocated:1;
 	enum printbuf_si	si_units:1;
 	bool			human_readable_units:1;
-	u8			tabstop;
-	u8			tabstops[4];
+	bool			has_indent_or_tabstops:1;
+	bool			suppress_indent_tabstop_handling:1;
+	u8			nr_tabstops;
+
+	/*
+	 * Do not modify directly: use printbuf_tabstop_add(),
+	 * printbuf_tabstop_get()
+	 */
+	u8			cur_tabstop;
+	u8			_tabstops[PRINTBUF_INLINE_TABSTOPS];
 };
 
 int printbuf_make_room(struct printbuf *, unsigned);
 const char *printbuf_str(const struct printbuf *);
 void printbuf_exit(struct printbuf *);
 
-void prt_newline(struct printbuf *);
+void printbuf_tabstops_reset(struct printbuf *);
+void printbuf_tabstop_pop(struct printbuf *);
+int printbuf_tabstop_push(struct printbuf *, unsigned);
+
 void printbuf_indent_add(struct printbuf *, unsigned);
 void printbuf_indent_sub(struct printbuf *, unsigned);
+
+void prt_newline(struct printbuf *);
 void prt_tab(struct printbuf *);
 void prt_tab_rjust(struct printbuf *);
+
 void prt_bytes_indented(struct printbuf *, const char *, unsigned);
 void prt_human_readable_u64(struct printbuf *, u64);
 void prt_human_readable_s64(struct printbuf *, s64);
@@ -241,7 +257,8 @@ static inline void printbuf_reset(struct printbuf *buf)
 	buf->pos		= 0;
 	buf->allocation_failure	= 0;
 	buf->indent		= 0;
-	buf->tabstop		= 0;
+	buf->nr_tabstops	= 0;
+	buf->cur_tabstop	= 0;
 }
 
 /**
diff --git a/lib/printbuf.c b/lib/printbuf.c
index 3fbb74754b48..2aa4a1b7294e 100644
--- a/lib/printbuf.c
+++ b/lib/printbuf.c
@@ -13,7 +13,7 @@
 #include <linux/string_helpers.h>
 #include <linux/printbuf.h>
 
-static inline size_t printbuf_linelen(struct printbuf *buf)
+static inline unsigned printbuf_linelen(struct printbuf *buf)
 {
 	return buf->pos - buf->last_newline;
 }
@@ -81,25 +81,43 @@ void printbuf_exit(struct printbuf *buf)
 }
 EXPORT_SYMBOL(printbuf_exit);
 
-void prt_newline(struct printbuf *buf)
+void printbuf_tabstops_reset(struct printbuf *buf)
 {
-	unsigned i;
-
-	printbuf_make_room(buf, 1 + buf->indent);
-
-	__prt_char(buf, '\n');
+	buf->nr_tabstops = 0;
+}
+EXPORT_SYMBOL(printbuf_tabstops_reset);
 
-	buf->last_newline	= buf->pos;
+void printbuf_tabstop_pop(struct printbuf *buf)
+{
+	if (buf->nr_tabstops)
+		--buf->nr_tabstops;
+}
+EXPORT_SYMBOL(printbuf_tabstop_pop);
 
-	for (i = 0; i < buf->indent; i++)
-		__prt_char(buf, ' ');
+/*
+ * printbuf_tabstop_set - add a tabstop, n spaces from the previous tabstop
+ *
+ * @buf: printbuf to control
+ * @spaces: number of spaces from previous tabpstop
+ *
+ * In the future this function may allocate memory if setting more than
+ * PRINTBUF_INLINE_TABSTOPS or setting tabstops more than 255 spaces from start
+ * of line.
+ */
+int printbuf_tabstop_push(struct printbuf *buf, unsigned spaces)
+{
+	unsigned prev_tabstop = buf->nr_tabstops
+		? buf->_tabstops[buf->nr_tabstops - 1]
+		: 0;
 
-	printbuf_nul_terminate(buf);
+	if (WARN_ON(buf->nr_tabstops >= ARRAY_SIZE(buf->_tabstops)))
+		return -EINVAL;
 
-	buf->last_field		= buf->pos;
-	buf->tabstop = 0;
+	buf->_tabstops[buf->nr_tabstops++] = prev_tabstop + spaces;
+	buf->has_indent_or_tabstops = true;
+	return 0;
 }
-EXPORT_SYMBOL(prt_newline);
+EXPORT_SYMBOL(printbuf_tabstop_push);
 
 /**
  * printbuf_indent_add - add to the current indent level
@@ -116,8 +134,9 @@ void printbuf_indent_add(struct printbuf *buf, unsigned spaces)
 		spaces = 0;
 
 	buf->indent += spaces;
-	while (spaces--)
-		prt_char(buf, ' ');
+	prt_chars(buf, ' ', spaces);
+
+	buf->has_indent_or_tabstops = true;
 }
 EXPORT_SYMBOL(printbuf_indent_add);
 
@@ -140,23 +159,50 @@ void printbuf_indent_sub(struct printbuf *buf, unsigned spaces)
 		printbuf_nul_terminate(buf);
 	}
 	buf->indent -= spaces;
+
+	if (!buf->indent && !buf->nr_tabstops)
+		buf->has_indent_or_tabstops = false;
 }
 EXPORT_SYMBOL(printbuf_indent_sub);
 
-static inline bool tabstop_is_set(struct printbuf *buf)
+void prt_newline(struct printbuf *buf)
 {
-	return buf->tabstop < ARRAY_SIZE(buf->tabstops) &&
-		buf->tabstops[buf->tabstop];
+	unsigned i;
+
+	printbuf_make_room(buf, 1 + buf->indent);
+
+	__prt_char(buf, '\n');
+
+	buf->last_newline	= buf->pos;
+
+	for (i = 0; i < buf->indent; i++)
+		__prt_char(buf, ' ');
+
+	printbuf_nul_terminate(buf);
+
+	buf->last_field		= buf->pos;
+	buf->cur_tabstop	= 0;
+}
+EXPORT_SYMBOL(prt_newline);
+
+/*
+ * Returns spaces from start of line, if set, or 0 if unset:
+ */
+static inline unsigned cur_tabstop(struct printbuf *buf)
+{
+	return buf->cur_tabstop < buf->nr_tabstops
+		? buf->_tabstops[buf->cur_tabstop]
+		: 0;
 }
 
 static void __prt_tab(struct printbuf *out)
 {
-	int spaces = max_t(int, 0, out->tabstops[out->tabstop] - printbuf_linelen(out));
+	int spaces = max_t(int, 0, cur_tabstop(out) - printbuf_linelen(out));
 
 	prt_chars(out, ' ', spaces);
 
 	out->last_field = out->pos;
-	out->tabstop++;
+	out->cur_tabstop++;
 }
 
 /**
@@ -168,7 +214,7 @@ static void __prt_tab(struct printbuf *out)
  */
 void prt_tab(struct printbuf *out)
 {
-	if (WARN_ON(!tabstop_is_set(out)))
+	if (WARN_ON(!cur_tabstop(out)))
 		return;
 
 	__prt_tab(out);
@@ -177,28 +223,27 @@ EXPORT_SYMBOL(prt_tab);
 
 static void __prt_tab_rjust(struct printbuf *buf)
 {
-	if (printbuf_linelen(buf) < buf->tabstops[buf->tabstop]) {
-		unsigned move = buf->pos - buf->last_field;
-		unsigned shift = buf->tabstops[buf->tabstop] -
-			printbuf_linelen(buf);
+	unsigned move = buf->pos - buf->last_field;
+	int pad = (int) cur_tabstop(buf) - (int) printbuf_linelen(buf);
 
-		printbuf_make_room(buf, shift);
+	if (pad > 0) {
+		printbuf_make_room(buf, pad);
 
-		if (buf->last_field + shift < buf->size)
-			memmove(buf->buf + buf->last_field + shift,
+		if (buf->last_field + pad < buf->size)
+			memmove(buf->buf + buf->last_field + pad,
 				buf->buf + buf->last_field,
-				min(move, buf->size - 1 - buf->last_field - shift));
+				min(move, buf->size - 1 - buf->last_field - pad));
 
 		if (buf->last_field < buf->size)
 			memset(buf->buf + buf->last_field, ' ',
-			       min(shift, buf->size - buf->last_field));
+			       min((unsigned) pad, buf->size - buf->last_field));
 
-		buf->pos += shift;
+		buf->pos += pad;
 		printbuf_nul_terminate(buf);
 	}
 
 	buf->last_field = buf->pos;
-	buf->tabstop++;
+	buf->cur_tabstop++;
 }
 
 /**
@@ -212,7 +257,7 @@ static void __prt_tab_rjust(struct printbuf *buf)
  */
 void prt_tab_rjust(struct printbuf *buf)
 {
-	if (WARN_ON(!tabstop_is_set(buf)))
+	if (WARN_ON(!cur_tabstop(buf)))
 		return;
 
 	__prt_tab_rjust(buf);
@@ -236,6 +281,11 @@ void prt_bytes_indented(struct printbuf *out, const char *str, unsigned count)
 	const char *unprinted_start = str;
 	const char *end = str + count;
 
+	if (!out->has_indent_or_tabstops || out->suppress_indent_tabstop_handling) {
+		prt_bytes(out, str, count);
+		return;
+	}
+
 	while (str != end) {
 		switch (*str) {
 		case '\n':
@@ -244,14 +294,14 @@ void prt_bytes_indented(struct printbuf *out, const char *str, unsigned count)
 			prt_newline(out);
 			break;
 		case '\t':
-			if (likely(tabstop_is_set(out))) {
+			if (likely(cur_tabstop(out))) {
 				prt_bytes(out, unprinted_start, str - unprinted_start);
 				unprinted_start = str + 1;
 				__prt_tab(out);
 			}
 			break;
 		case '\r':
-			if (likely(tabstop_is_set(out))) {
+			if (likely(cur_tabstop(out))) {
 				prt_bytes(out, unprinted_start, str - unprinted_start);
 				unprinted_start = str + 1;
 				__prt_tab_rjust(out);