Re: [Xen-devel] [PATCH 01/27 v10] xen/arm: vpl011: Define common ring buffer helper functions in console.h

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Adding Jan

On Fri, 22 Sep 2017, Bhupinder Thakur wrote:
> DEFINE_XEN_FLEX_RING(xencons) defines common helper functions such as
> xencons_queued() to tell the current size of the ring buffer,
> xencons_mask() to mask off the index, which are useful helper functions.
> pl011 emulation code will use these helper functions.
> 
> io/console.h includes io/ring.h which defines DEFINE_XEN_FLEX_RING.
> 
> In console/daemon/io.c, string.h had to be included before io/console.h
> because ring.h uses string functions.
> 
> Signed-off-by: Bhupinder Thakur <bhupinder.thakur@xxxxxxxxxx>
> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Acked-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Unfortunately this patch breaks the build on x86. The reason is that
DEFINE_XEN_FLEX_RING requires C99, and the current header checks in
xen/include/Makefile use ANSI C.

The only two headers to use DEFINE_XEN_FLEX_RING so far are pvcalls and
9pfs that are both explicitly marked as c99 in xen/include/Makefile, see
PUBLIC_C99_HEADERS.

One way to solve this problem would be to mark console.h as one of the
c99 headers, but I am guessing that Jan will want to keep it ANSI C.

In that case, we could make DEFINE_XEN_FLEX_RING ANSI C, which is ugly
but possible. It requires turning the static inline functions in ring.h
into macros.

Otherwise, we could take DEFINE_XEN_FLEX_RING(xencons) out of
io/console.h. We could move it to a new header file, and the new header
file could be C99.

Jan, do you have other suggestions?


> ---
> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> 
> Changes since v4:
> - Split this change in a separate patch.
> 
>  tools/console/daemon/io.c       | 2 +-
>  xen/include/public/io/console.h | 4 ++++
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/console/daemon/io.c b/tools/console/daemon/io.c
> index 7e474bb..e8033d2 100644
> --- a/tools/console/daemon/io.c
> +++ b/tools/console/daemon/io.c
> @@ -21,6 +21,7 @@
>  
>  #include "utils.h"
>  #include "io.h"
> +#include <string.h>
>  #include <xenevtchn.h>
>  #include <xengnttab.h>
>  #include <xenstore.h>
> @@ -29,7 +30,6 @@
>  
>  #include <stdlib.h>
>  #include <errno.h>
> -#include <string.h>
>  #include <poll.h>
>  #include <fcntl.h>
>  #include <unistd.h>
> diff --git a/xen/include/public/io/console.h b/xen/include/public/io/console.h
> index e2cd97f..5e45e1c 100644
> --- a/xen/include/public/io/console.h
> +++ b/xen/include/public/io/console.h
> @@ -27,6 +27,8 @@
>  #ifndef __XEN_PUBLIC_IO_CONSOLE_H__
>  #define __XEN_PUBLIC_IO_CONSOLE_H__
>  
> +#include "ring.h"
> +
>  typedef uint32_t XENCONS_RING_IDX;
>  
>  #define MASK_XENCONS_IDX(idx, ring) ((idx) & (sizeof(ring)-1))
> @@ -38,6 +40,8 @@ struct xencons_interface {
>      XENCONS_RING_IDX out_cons, out_prod;
>  };
>  
> +DEFINE_XEN_FLEX_RING(xencons);
> +
>  #endif /* __XEN_PUBLIC_IO_CONSOLE_H__ */
>  
>  /*
> -- 
> 2.7.4
> 

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