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

Kent Overstreet
2022-04-20T00:12:52Z

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@gmail.com>
Date: Tue Apr 19 17:29:43 2022 -0400

lib/printbuf: Switch to string_get_size()

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.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);