[PATCH] relay: fix bogus cast in subbuf_splice_actor()

[PATCH] relay: fix bogus cast in subbuf_splice_actor()

[Tom Zanussi]

The current code that sets the read position in subbuf_splice_actor may
give erroneous results if the buffer size isn't a power of 2.  This
patch fixes the problem.

Signed-off-by: Tom Zanussi <zanussi@us.ibm.com>

---
 relay.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/relay.c b/kernel/relay.c
index 3b299fb..7802697 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1074,7 +1074,9 @@ static int subbuf_splice_actor(struct file *in,
 	unsigned int pidx, poff, total_len, subbuf_pages, ret;
 	struct rchan_buf *rbuf = in->private_data;
 	unsigned int subbuf_size = rbuf->chan->subbuf_size;
-	size_t read_start = ((size_t)*ppos) % rbuf->chan->alloc_size;
+	uint64_t pos = (uint64_t) *ppos;
+	uint32_t alloc_size = (uint32_t) rbuf->chan->alloc_size;
+	size_t read_start = (size_t) do_div(pos, alloc_size);
 	size_t read_subbuf = read_start / subbuf_size;
 	size_t padding = rbuf->padding[read_subbuf];
 	size_t nonpad_end = read_subbuf * subbuf_size + subbuf_size - padding;

Re: [PATCH] relay: fix bogus cast in subbuf_splice_actor()

[Jens Axboe]

On Wed, Jul 11 2007, Tom Zanussi wrote:
> The current code that sets the read position in subbuf_splice_actor may
> give erroneous results if the buffer size isn't a power of 2.  This
> patch fixes the problem.

Thanks Tom, I just added this for my upstream branch, if you submit it
directly first, I'll just rebase without it again. Otherwise it'll go in
when I ask Linus to pull next.

-- 
Jens Axboe