linux-kernel - Re: [PATCH 1/4] lib/printbuf: New data structure for heap-allocated strings

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Date:   Tue, 19 Apr 2022 20:12:47 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, roman.gushchin@...ux.dev,
        hannes@...xchg.org
Subject: Re: [PATCH 1/4] lib/printbuf: New data structure for heap-allocated
 strings

On Tue, Apr 19, 2022 at 10:11:51PM +0100, Matthew Wilcox wrote:
> On Tue, Apr 19, 2022 at 04:31:59PM -0400, Kent Overstreet wrote:
> > +static const char si_units[] = "?kMGTPEZY";
> > +
> > +void pr_human_readable_u64(struct printbuf *buf, u64 v)
> 
> The person who wrote string_get_size() spent a lot more time thinking
> about corner-cases than you did ;-)

Didn't know about that until today :)

Just commited this:

commit 3cf1cb86ee4c4a7e75bcd52082ba0df1c436d692
Author: Kent Overstreet <kent.overstreet@...il.com>
Date:   Tue Apr 19 17:29:43 2022 -0400

    lib/printbuf: Switch to string_get_size()
    
    Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>

diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h
index 84a271446d..2d23506114 100644
--- a/include/linux/printbuf.h
+++ b/include/linux/printbuf.h
@@ -91,11 +91,13 @@ struct printbuf {
 	enum printbuf_units	units:8;
 	u8			atomic;
 	bool			allocation_failure:1;
+	/* SI units (10^3), or 2^10: */
+	enum string_size_units	human_readable_units:1;
 	u8			tabstop;
 	u8			tabstops[4];
 };
 
-#define PRINTBUF ((struct printbuf) { NULL })
+#define PRINTBUF ((struct printbuf) { .human_readable_units = STRING_UNITS_2 })
 
 /**
  * printbuf_exit - exit a printbuf, freeing memory it owns and poisoning it
diff --git a/lib/printbuf.c b/lib/printbuf.c
index a9d5dff81e..ecbce6670f 100644
--- a/lib/printbuf.c
+++ b/lib/printbuf.c
@@ -10,6 +10,7 @@
 
 #include <linux/log2.h>
 #include <linux/printbuf.h>
+#include <linux/string_helpers.h>
 
 static inline size_t printbuf_remaining(struct printbuf *buf)
 {
@@ -144,27 +145,11 @@ void pr_tab_rjust(struct printbuf *buf)
 }
 EXPORT_SYMBOL(pr_tab_rjust);
 
-static const char si_units[] = "?kMGTPEZY";
-
 void pr_human_readable_u64(struct printbuf *buf, u64 v)
 {
-	int u, t = 0;
-
-	for (u = 0; v >= 1024; u++) {
-		t = v & ~(~0U << 10);
-		v >>= 10;
-	}
-
-	pr_buf(buf, "%llu", v);
-
-	/*
-	 * 103 is magic: t is in the range [-1023, 1023] and we want
-	 * to turn it into [-9, 9]
-	 */
-	if (u && t && v < 100 && v > -100)
-		pr_buf(buf, ".%i", t / 103);
-	if (u)
-		pr_char(buf, si_units[u]);
+	printbuf_realloc(buf, 10);
+	string_get_size(v, 1, buf->human_readable_units, buf->buf + buf->pos,
+			printbuf_remaining(buf));
 }
 EXPORT_SYMBOL(pr_human_readable_u64);