Re: [PATCH] blkiomon: fix unaligned accesses on ia64

[Martin Peschke <mpeschke@linux.vnet.ibm.com>]

Eric,
I think you have got a valid point. But I would like to make two small
changes to you patch:

A new blkiomon version number is needed then. Not a perfect solution for
reflecting this change, but good enough at least for our tool that
consumes blkiomon data through a message queue.

Moving the __u32 device member instead of a new padding field should be
fine.

I have tested the patch below. If it's fine with you, please just push
it upstream through Jens.

Thanks,
Martin



Signed-off-by: Martin Peschke <mpeschke@linux.vnet.ibm.com>

---
 blkiomon.c |    2 +-
 blkiomon.h |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/blkiomon.h
+++ b/blkiomon.h
@@ -34,6 +34,7 @@ struct blkiomon_stat {
 	__u64 time;
 	__u32 size_hist[BLKIOMON_SIZE_BUCKETS];
 	__u32 d2c_hist[BLKIOMON_D2C_BUCKETS];
+	__u32 device;
 	struct minmax size_r;
 	struct minmax size_w;
 	struct minmax d2c_r;
@@ -41,8 +42,7 @@ struct blkiomon_stat {
 	struct minmax thrput_r;
 	struct minmax thrput_w;
 	__u64 bidir;
-	__u32 device;
-} __attribute__ ((packed));
+};
 
 static struct histlog2 size_hist = {
 	.first = 0,
--- a/blkiomon.c
+++ b/blkiomon.c
@@ -71,7 +71,7 @@ struct output {
 	int pipe;
 };
 
-static char blkiomon_version[] = "0.2";
+static char blkiomon_version[] = "0.3";
 
 static FILE *ifp;
 static int interval = -1;




On Wed, 2009-05-06 at 16:49 -0500, Eric Sandeen wrote: 
> commit 7aa3ebcec011bfe9cc60d6476252c03376a37551 packed
> the blkiomon_stat structure so that traces from one 
> arch could be analyzed on another (in truth only x86
> is different, at least from x86_64/ia64/ppc/ppc64/s390/s390x)
> 
> Rather than packing it, which generates unaligned access
> warnings on ia64, just pad the structure out so that it's
> naturally aligned on all arches.
> 
> Martin, care to test this to be sure it still works for
> you?  (I'm not sure if we might also need a 4 byte pad on 
> the end of the structure to align the containing structure...)
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> diff --git a/blkiomon.h b/blkiomon.h
> index 2e430a6..ae48b4c 100644
> --- a/blkiomon.h
> +++ b/blkiomon.h
> @@ -34,6 +34,7 @@ struct blkiomon_stat {
>  	__u64 time;
>  	__u32 size_hist[BLKIOMON_SIZE_BUCKETS];
>  	__u32 d2c_hist[BLKIOMON_D2C_BUCKETS];
> +	__u32 pad; /* Align the structure */
>  	struct minmax size_r;
>  	struct minmax size_w;
>  	struct minmax d2c_r;
> @@ -42,7 +43,7 @@ struct blkiomon_stat {
>  	struct minmax thrput_w;
>  	__u64 bidir;
>  	__u32 device;
> -} __attribute__ ((packed));
> +};
> 
>  static struct histlog2 size_hist = {
>  	.first = 0,
>