bcache: fix bch_hprint crash and improve output

Most importantly, solve a crash where %llu was used to format signed
numbers.  This would cause a buffer overflow when reading sysfs
writeback_rate_debug, as only 20 bytes were allocated for this and
%llu writes 20 characters plus a null.

Always use the units mechanism rather than having different output
paths for simplicity.

Also, correct problems with display output where 1.10 was a larger
number than 1.09, by multiplying by 10 and then dividing by 1024 instead
of dividing by 100.  (Remainders of >= 1000 would print as .10).

Minor changes: Always display the decimal point instead of trying to
omit it based on number of digits shown.  Decide what units to use
based on 1000 as a threshold, not 1024 (in other words, always print
at most 3 digits before the decimal point).

Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reported-by: Dmitry Yu Okunev <dyokunev@ut.mephi.ru>
Acked-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Coly Li <colyli@suse.de>
Cc: stable@vger.kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
index 8c3a938f4bf068cdc648327c410c18585b59cd4a..176d3c2ef5f5cf8b69ed425c504a204ca520dffb 100644 (file)
--- a/drivers/md/bcache/util.c
+++ b/drivers/md/bcache/util.c
@@ -74,24 +74,44 @@ STRTO_H(strtouint, unsigned int)
 STRTO_H(strtoll, long long)
 STRTO_H(strtoull, unsigned long long)
 
+/**
+ * bch_hprint() - formats @v to human readable string for sysfs.
+ *
+ * @v - signed 64 bit integer
+ * @buf - the (at least 8 byte) buffer to format the result into.
+ *
+ * Returns the number of bytes used by format.
+ */
 ssize_t bch_hprint(char *buf, int64_t v)
 {
        static const char units[] = "?kMGTPEZY";
-       char dec[4] = "";
-       int u, t = 0;
-
-       for (u = 0; v >= 1024 || v <= -1024; u++) {
-               t = v & ~(~0 << 10);
-               v >>= 10;
-       }
-
-       if (!u)
-               return sprintf(buf, "%llu", v);
-
-       if (v < 100 && v > -100)
-               snprintf(dec, sizeof(dec), ".%i", t / 100);
-
-       return sprintf(buf, "%lli%s%c", v, dec, units[u]);
+       int u = 0, t;
+
+       uint64_t q;
+
+       if (v < 0)
+               q = -v;
+       else
+               q = v;
+
+       /* For as long as the number is more than 3 digits, but at least
+        * once, shift right / divide by 1024.  Keep the remainder for
+        * a digit after the decimal point.
+        */
+       do {
+               u++;
+
+               t = q & ~(~0 << 10);
+               q >>= 10;
+       } while (q >= 1000);
+
+       if (v < 0)
+               /* '-', up to 3 digits, '.', 1 digit, 1 character, null;
+                * yields 8 bytes.
+                */
+               return sprintf(buf, "-%llu.%i%c", q, t * 10 / 1024, units[u]);
+       else
+               return sprintf(buf, "%llu.%i%c", q, t * 10 / 1024, units[u]);
 }
 
 ssize_t bch_snprint_string_list(char *buf, size_t size, const char * const list[],