sd, mmc, virtio_blk, string_helpers: fix block size units

The current string_get_size() overflows when the device size goes over
2^64 bytes because the string helper routine computes the suffix from
the size in bytes.  However, the entirety of Linux thinks in terms of
blocks, not bytes, so this will artificially induce an overflow on very
large devices.  Fix this by making the function string_get_size() take
blocks and the block size instead of bytes.  This should allow us to
keep working until the current SCSI standard overflows.

Also fix virtio_blk and mmc (both of which were also artificially
multiplying by the block size to pass a byte side to string_get_size()).

The mathematics of this is pretty simple:  we're taking a product of
size in blocks (S) and block size (B) and trying to re-express this in
exponential form: S*B = R*N^E (where N, the exponent is either 1000 or
1024) and R < N.  Mathematically, S = RS*N^ES and B=RB*N^EB, so if RS*RB
< N it's easy to see that S*B = RS*RB*N^(ES+EB).  However, if RS*BS > N,
we can see that this can be re-expressed as RS*BS = R*N (where R =
RS*BS/N < N) so the whole exponent becomes R*N^(ES+EB+1)

[jejb: fix incorrect 32 bit do_div spotted by kbuild test robot <fengguang.wu@intel.com>]
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

1 files changed, 48 insertions, 20 deletions

diff --git a/lib/string_helpers.c b/lib/string_helpers.c
index 8f8c4417f228..4a913ec3acf9 100644
--- a/lib/string_helpers.c
+++ b/lib/string_helpers.c
@@ -4,6 +4,7 @@
  * Copyright 31 August 2008 James Bottomley
  * Copyright (C) 2013, Intel Corporation
  */
+#include <linux/bug.h>
 #include <linux/kernel.h>
 #include <linux/math64.h>
 #include <linux/export.h>
@@ -14,7 +15,8 @@
 
 /**
  * string_get_size - get the size in the specified units
- * @size:       The size to be converted
+ * @size:       The size to be converted in blocks
+ * @blk_size:   Size of the block (use 1 for size in bytes)
  * @units:      units to use (powers of 1000 or 1024)
  * @buf:        buffer to format to
  * @len:        length of buffer
@@ -24,14 +26,14 @@
  * at least 9 bytes and will always be zero terminated.
  *
  */
-void string_get_size(u64 size, const enum string_size_units units,
+void string_get_size(u64 size, u64 blk_size, const enum string_size_units units,
                      char *buf, int len)
 {
         static const char *const units_10[] = {
-                "B", "kB", "MB", "GB", "TB", "PB", "EB"
+                "B", "kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"
         };
         static const char *const units_2[] = {
-                "B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB"
+                "B", "KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"
         };
         static const char *const *const units_str[] = {
                 [STRING_UNITS_10] = units_10,
@@ -42,31 +44,57 @@ void string_get_size(u64 size, const enum string_size_units units,
                 [STRING_UNITS_2] = 1024,
         };
         int i, j;
-        u32 remainder = 0, sf_cap;
+        u32 remainder = 0, sf_cap, exp;
         char tmp[8];
+        const char *unit;
 
         tmp[0] = '\0';
         i = 0;
-        if (size >= divisor[units]) {
-                while (size >= divisor[units]) {
-                        remainder = do_div(size, divisor[units]);
-                        i++;
-                }
+        if (!size)
+                goto out;
 
-                sf_cap = size;
-                for (j = 0; sf_cap*10 < 1000; j++)
-                        sf_cap *= 10;
+        while (blk_size >= divisor[units]) {
+                remainder = do_div(blk_size, divisor[units]);
+                i++;
+        }
 
-                if (j) {
-                        remainder *= 1000;
-                        remainder /= divisor[units];
-                        snprintf(tmp, sizeof(tmp), ".%03u", remainder);
-                        tmp[j+1] = '\0';
-                }
+        exp = divisor[units] / (u32)blk_size;
+        if (size >= exp) {
+                remainder = do_div(size, divisor[units]);
+                remainder *= blk_size;
+                i++;
+        } else {
+                remainder *= size;
+        }
+
+        size *= blk_size;
+        size += remainder / divisor[units];
+        remainder %= divisor[units];
+
+        while (size >= divisor[units]) {
+                remainder = do_div(size, divisor[units]);
+                i++;
         }
 
+        sf_cap = size;
+        for (j = 0; sf_cap*10 < 1000; j++)
+                sf_cap *= 10;
+
+        if (j) {
+                remainder *= 1000;
+                remainder /= divisor[units];
+                snprintf(tmp, sizeof(tmp), ".%03u", remainder);
+                tmp[j+1] = '\0';
+        }
+
+ out:
+        if (i >= ARRAY_SIZE(units_2))
+                unit = "UNK";
+        else
+                unit = units_str[units][i];
+
         snprintf(buf, len, "%u%s %s", (u32)size,
-                 tmp, units_str[units][i]);
+                 tmp, unit);
 }
 EXPORT_SYMBOL(string_get_size);