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, 5 insertions, 4 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 655e570b9b31..5ea2f0bbbc7c 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -342,7 +342,7 @@ static void virtblk_config_changed_work(struct work_struct *work)
 	struct request_queue *q = vblk->disk->queue;
 	char cap_str_2[10], cap_str_10[10];
 	char *envp[] = { "RESIZE=1", NULL };
-	u64 capacity, size;
+	u64 capacity;
 
 	/* Host must always specify the capacity. */
 	virtio_cread(vdev, struct virtio_blk_config, capacity, &capacity);
@@ -354,9 +354,10 @@ static void virtblk_config_changed_work(struct work_struct *work)
 		capacity = (sector_t)-1;
 	}
 
-	size = capacity * queue_logical_block_size(q);
-	string_get_size(size, STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
-	string_get_size(size, STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));
+	string_get_size(capacity, queue_logical_block_size(q),
+			STRING_UNITS_2, cap_str_2, sizeof(cap_str_2));
+	string_get_size(capacity, queue_logical_block_size(q),
+			STRING_UNITS_10, cap_str_10, sizeof(cap_str_10));
 
 	dev_notice(&vdev->dev,
 		  "new size: %llu %d-byte logical blocks (%s/%s)\n",