[PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[Julien Grall]

On ARM (32 bits and 64 bits), the double-word is 8-bytes aligned. This will
result on different structure from Xen and Linux repositories.

As Linux is using __packed__ attribute, it must have a 4-bytes padding before
each "id" field.

This change breaks guest block support with older kernel. IMHO, it's acceptable
because Xen on ARM is still on Tech Preview and the hypercall ABI is not yet
freezed.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Cc: Roger Pau Monne <roger.pau@citrix.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

---

This patch is the rework of "xen-block: correctly define structures in public
headers" sent by Roger (see https://lkml.org/lkml/2013/12/3/155).
---
 include/xen/interface/io/blkif.h |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
index 65e1209..08e8e9d 100644
--- a/include/xen/interface/io/blkif.h
+++ b/include/xen/interface/io/blkif.h
@@ -146,7 +146,7 @@ struct blkif_request_segment_aligned {
 struct blkif_request_rw {
 	uint8_t        nr_segments;  /* number of segments                   */
 	blkif_vdev_t   handle;       /* only for read/write requests         */
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
 	uint32_t       _pad1;	     /* offsetof(blkif_request,u.rw.id) == 8 */
 #endif
 	uint64_t       id;           /* private guest value, echoed in resp  */
@@ -163,7 +163,7 @@ struct blkif_request_discard {
 	uint8_t        flag;         /* BLKIF_DISCARD_SECURE or zero.        */
 #define BLKIF_DISCARD_SECURE (1<<0)  /* ignored if discard-secure=0          */
 	blkif_vdev_t   _pad1;        /* only for read/write requests         */
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
 	uint32_t       _pad2;        /* offsetof(blkif_req..,u.discard.id)==8*/
 #endif
 	uint64_t       id;           /* private guest value, echoed in resp  */
@@ -175,7 +175,7 @@ struct blkif_request_discard {
 struct blkif_request_other {
 	uint8_t      _pad1;
 	blkif_vdev_t _pad2;        /* only for read/write requests         */
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
 	uint32_t     _pad3;        /* offsetof(blkif_req..,u.other.id)==8*/
 #endif
 	uint64_t     id;           /* private guest value, echoed in resp  */
@@ -184,7 +184,7 @@ struct blkif_request_other {
 struct blkif_request_indirect {
 	uint8_t        indirect_op;
 	uint16_t       nr_segments;
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
 	uint32_t       _pad1;        /* offsetof(blkif_...,u.indirect.id) == 8 */
 #endif
 	uint64_t       id;
@@ -192,7 +192,7 @@ struct blkif_request_indirect {
 	blkif_vdev_t   handle;
 	uint16_t       _pad2;
 	grant_ref_t    indirect_grefs[BLKIF_MAX_INDIRECT_PAGES_PER_REQUEST];
-#ifdef CONFIG_X86_64
+#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
 	uint32_t      _pad3;         /* make it 64 byte aligned */
 #else
 	uint64_t      _pad3;         /* make it 64 byte aligned */
-- 
1.7.10.4

[Xen-devel] [PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[Jan Beulich]

>>> On 03.12.13 at 16:09, Julien Grall <julien.grall@linaro.org> wrote:
> --- a/include/xen/interface/io/blkif.h
> +++ b/include/xen/interface/io/blkif.h
> @@ -146,7 +146,7 @@ struct blkif_request_segment_aligned {
>  struct blkif_request_rw {
>  	uint8_t        nr_segments;  /* number of segments                   */
>  	blkif_vdev_t   handle;       /* only for read/write requests         */
> -#ifdef CONFIG_X86_64
> +#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)

Perhaps using

#ifndef CONFIG_X86_32

would be the better one, assuming that we won't add further
non-64-bit-clean ABI variants?

Jan

[Xen-devel] [PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[Julien Grall]

On 12/03/2013 03:15 PM, Jan Beulich wrote:
>>>> On 03.12.13 at 16:09, Julien Grall <julien.grall@linaro.org> wrote:
>> --- a/include/xen/interface/io/blkif.h
>> +++ b/include/xen/interface/io/blkif.h
>> @@ -146,7 +146,7 @@ struct blkif_request_segment_aligned {
>>  struct blkif_request_rw {
>>  	uint8_t        nr_segments;  /* number of segments                   */
>>  	blkif_vdev_t   handle;       /* only for read/write requests         */
>> -#ifdef CONFIG_X86_64
>> +#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
> 
> Perhaps using
> 
> #ifndef CONFIG_X86_32
> 
> would be the better one, assuming that we won't add further
> non-64-bit-clean ABI variants?

I'm fine with this solution. I will resend the patch.

-- 
Julien Grall

[Xen-devel] [PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[Ian Campbell]

On Tue, 2013-12-03 at 15:28 +0000, Julien Grall wrote:
> On 12/03/2013 03:15 PM, Jan Beulich wrote:
> >>>> On 03.12.13 at 16:09, Julien Grall <julien.grall@linaro.org> wrote:
> >> --- a/include/xen/interface/io/blkif.h
> >> +++ b/include/xen/interface/io/blkif.h
> >> @@ -146,7 +146,7 @@ struct blkif_request_segment_aligned {
> >>  struct blkif_request_rw {
> >>  	uint8_t        nr_segments;  /* number of segments                   */
> >>  	blkif_vdev_t   handle;       /* only for read/write requests         */
> >> -#ifdef CONFIG_X86_64
> >> +#if defined(CONFIG_X86_64) || defined(CONFIG_ARM) || defined(CONFIG_ARM64)
> > 
> > Perhaps using
> > 
> > #ifndef CONFIG_X86_32
> > 
> > would be the better one, assuming that we won't add further
> > non-64-bit-clean ABI variants?
> 
> I'm fine with this solution. I will resend the patch.

Just a random thought but what about using the CONFIG_$ARCH to define a
more semantic name, like HAVE_4_BYTE_ALIGNED_QUAD_WORDS, or whichever
terminology for an 8-byte type is appropriate in the context.

Maybe Linux even already has such a #define?

Ian.

[Xen-devel] [PATCH] xen/block: Correctly define structures in public headers on ARM32 and ARM64

[One Thousand Gnomes]

> Just a random thought but what about using the CONFIG_$ARCH to define a
> more semantic name, like HAVE_4_BYTE_ALIGNED_QUAD_WORDS, or whichever
> terminology for an 8-byte type is appropriate in the context.
> 
> Maybe Linux even already has such a #define?

It doesn't need one. It's written in GNU C so we have __alignof__.

See

http://gcc.gnu.org/onlinedocs/gcc/Alignment.html