lib/printbuf: Tabstops, indenting

This patch adds two new features to printbuf for structured formatting:

 - Indent level: the indent level, as a number of spaces, may be
   increased with pr_indent_add() and decreased with pr_indent_sub().

   Subsequent lines, when started with pr_newline() (not "\n", although
   that may change) will then be intended according to the current
   indent level. This helps with pretty-printers that structure a large
   amonut of data across multiple lines and multiple functions.

 - Tabstops: Tabstops may be set by assigning to the printbuf->tabstops
   array.

   Then, pr_tab() may be used to advance to the next tabstop, printing
   as many spaces as required - leaving previous output left justified
   to the previous tabstop. pr_tab_rjust() advances to the next tabstop
   but inserts the spaces just after the previous tabstop - right
   justifying the previously-outputted text to the next tabstop.

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

1 files changed, 28 insertions, 0 deletions

diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h
index b7fb51375d9b..5d32a31295f0 100644
--- a/include/linux/printbuf.h
+++ b/include/linux/printbuf.h
@@ -36,6 +36,23 @@
  * memory allocation failure we usually don't want to bail out and unwind - we
  * want to print what we've got, on a best-effort basis. But code that does want
  * to return -ENOMEM may check printbuf.allocation_failure.
+ *
+ * Indenting, tabstops:
+ *
+ * To aid is writing multi-line pretty printers spread across multiple
+ * functions, printbufs track the current indent level.
+ *
+ * printbuf_indent_push() and printbuf_indent_pop() increase and decrease the current indent
+ * level, respectively.
+ *
+ * To use tabstops, set printbuf->tabstops[]; they are in units of spaces, from
+ * start of line. Once set, prt_tab() will output spaces up to the next tabstop.
+ * prt_tab_rjust() will also advance the current line of text up to the next
+ * tabstop, but it does so by shifting text since the previous tabstop up to the
+ * next tabstop - right justifying it.
+ *
+ * Make sure you use prt_newline() instead of \n in the format string for indent
+ * level and tabstops to work corretly.
  */
 
 #include <linux/kernel.h>
@@ -45,18 +62,29 @@ struct printbuf {
 	char			*buf;
 	unsigned		size;
 	unsigned		pos;
+	unsigned		last_newline;
+	unsigned		last_field;
+	unsigned		indent;
 	/*
 	 * If nonzero, allocations will be done with GFP_ATOMIC:
 	 */
 	u8			atomic;
 	bool			allocation_failure:1;
 	bool			heap_allocated:1;
+	u8			tabstop;
+	u8			tabstops[4];
 };
 
 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_indent_add(struct printbuf *, unsigned);
+void printbuf_indent_sub(struct printbuf *, unsigned);
+void prt_tab(struct printbuf *);
+void prt_tab_rjust(struct printbuf *);
+
 /* Initializer for a heap allocated printbuf: */
 #define PRINTBUF ((struct printbuf) { .heap_allocated = true })