On 08/04/2019 11:33, David Laight wrote:
From: Robin Murphy
Sent: 08 April 2019 11:24
On 07/04/2019 05:31, Sai Prakash Ranjan wrote:
On 4/5/2019 6:44 PM, David Laight wrote:
From: Sai Prakash Ranjan
diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
index 93ce3aa740a9..21a5838f6e67 100644
--- a/drivers/hwtracing/stm/core.c
+++ b/drivers/hwtracing/stm/core.c
@@ -168,7 +168,7 @@ static int stp_master_alloc(struct stm_device
*stm, unsigned int idx)
struct stp_master *master;
size_t size;
- size = ALIGN(stm->data->sw_nchannels, 8) / 8;
+ size = ALIGN(stm->data->sw_nchannels, STM_MASTER_SZ) /
STM_MASTER_SZ;
I'm not sure that using STP_MASTER_SZ improves readability at all.
I thought it was better to have a macro than directly specifying
sizeof(unsigned long), anyways I can change it.
Is there something that gives the size of a bitmap for 'n' items?
Not sure if there is something.
If you were to ask the question "how does the bitmap code itself know
what the total size of a bitmap is?", that would quickly lead you
towards BITS_TO_LONGS() ;)
And given that stp_master::chan_map is already an appropriate type, that
suggests simplifying the entire calculation down to something neat and
tidy like:
size = offsetof(struct stp_master, chan_map[BITS_TO_LONGS(stm->data->sw_nchannels)]);
Except that is invalid.
You can't use offsetof() with something that isn't a compile time constant.
Oh, I see the standard does actually say that, although there seem to be
enough non-constant uses in the kernel to suggest that it still works in
practice.
However, while writing the above I was still trying to remember the
other thing I'd seen for handling precisely this variable-sized-struct
situation, which I've now found again, namely struct_size(). I guess now
I understand why that isn't implemented in terms of offsetof(), thanks
for the nudge :)
Robin.
