linux-kernel - Re: [PATCH v06 27/36] uapi xen/gntdev.h: include xen/privcmd.h and define grant_ref

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Date:   Mon, 21 Aug 2017 10:31:17 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>,
        Mikko Rapeli <mikko.rapeli@....fi>,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v06 27/36] uapi xen/gntdev.h: include xen/privcmd.h and
 define grant_ref_t

On 08/21/2017 09:33 AM, Juergen Gross wrote:
> On 06/08/17 18:44, Mikko Rapeli wrote:
>> Both are needed to compile <xen/gntdev.h> in userspace. Fixes these
>> userspace compile errors:
>>
>> xen/gntdev.h:151:4: error: unknown type name ‘grant_ref_t’
>>     grant_ref_t ref;
>>     ^
>> xen/gntdev.h:153:4: error: unknown type name ‘domid_t’
>>     domid_t domid;
>>     ^
>>
>> Signed-off-by: Mikko Rapeli <mikko.rapeli@....fi>
>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Cc: Juergen Gross <jgross@...e.com>
>> Cc: xen-devel@...ts.xenproject.org
>> ---
>>  include/uapi/xen/gntdev.h           | 6 ++++++
>>  include/xen/interface/grant_table.h | 6 +-----
>>  2 files changed, 7 insertions(+), 5 deletions(-)
>>
>> diff --git a/include/uapi/xen/gntdev.h b/include/uapi/xen/gntdev.h
>> index d0661977667e..f208706b07c9 100644
>> --- a/include/uapi/xen/gntdev.h
>> +++ b/include/uapi/xen/gntdev.h
>> @@ -34,6 +34,12 @@
>>  #define __LINUX_PUBLIC_GNTDEV_H__
>>  
>>  #include <linux/types.h>
>> +#include <xen/privcmd.h>
>> +
>> +/*
>> + * Reference to a grant entry in a specified domain's grant table.
>> + */
>> +typedef __u32 grant_ref_t;
>>  
>>  struct ioctl_gntdev_grant_ref {
>>  	/* The domain ID of the grant to be mapped. */
>> diff --git a/include/xen/interface/grant_table.h b/include/xen/interface/grant_table.h
>> index 7fb7112d667c..29b3724aec2c 100644
>> --- a/include/xen/interface/grant_table.h
>> +++ b/include/xen/interface/grant_table.h
>> @@ -29,6 +29,7 @@
>>  #define __XEN_PUBLIC_GRANT_TABLE_H__
>>  
>>  #include <xen/interface/xen.h>
>> +#include <uapi/xen/gntdev.h> /* for grant_ref_t */
> Hmm, I really don't like this. We import the Xen headers from the Xen
> source repository. The Xen specific types shouldn't be taken from
> non-Xen headers.
>
>>  
>>  /***********************************
>>   * GRANT TABLE REPRESENTATION
>> @@ -85,11 +86,6 @@
>>   */
>>  
>>  /*
>> - * Reference to a grant entry in a specified domain's grant table.
>> - */
>> -typedef uint32_t grant_ref_t;
>> -
>> -/*
>>   * A grant table comprises a packed array of grant entries in one or more
>>   * page frames shared between Xen and a guest.
>>   * [XEN]: This field is written by Xen and read by the sharing guest.
>>
> I'd rather use __u32 instead of grant_ref_t in the uapi headers.
>
> Boris, what do you think?

I agree that including a non-Xen file into include/xen/interface is not
especially desirable.

Can we ifdef __KERNEL__grant_ref_t usage in uapi header, with else
clause using __u32? And maybe stick BUILD_BUG_ON somewhere to check that
sizes are still the same ?

-boris

-boris