Re: [PATCH v4 04/16] libs/guest: Use a single write_exact in write_headers

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Wed, Jun 03, 2026 at 02:05:51PM +0100, Frediano Ziglio wrote:
> From: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
> 
> Reduce number of syscalls.

... by coalescing the image and the domain headers into a single IO
vector array.

> 
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

> --
> Changes since v2:
> - change prefix in subject.
> ---
>  tools/libs/guest/xg_sr_save.c | 37 +++++++++++++++++------------------
>  1 file changed, 18 insertions(+), 19 deletions(-)
> 
> diff --git a/tools/libs/guest/xg_sr_save.c b/tools/libs/guest/xg_sr_save.c
> index 62a39dfecc..8c4e760f8d 100644
> --- a/tools/libs/guest/xg_sr_save.c
> +++ b/tools/libs/guest/xg_sr_save.c
> @@ -10,17 +10,22 @@ static int write_headers(struct xc_sr_context *ctx, 
> uint16_t guest_type)
>  {
>      xc_interface *xch = ctx->xch;
>      int32_t xen_version = xc_version(xch, XENVER_version, NULL);
> -    struct xc_sr_ihdr ihdr = {
> -        .marker  = IHDR_MARKER,
> -        .id      = htonl(IHDR_ID),
> -        .version = htonl(3),
> -        .options = htons(IHDR_OPT_LITTLE_ENDIAN),
> -    };
> -    struct xc_sr_dhdr dhdr = {
> -        .type       = guest_type,
> -        .page_shift = XC_PAGE_SHIFT,
> -        .xen_major  = (xen_version >> 16) & 0xffff,
> -        .xen_minor  = (xen_version)       & 0xffff,
> +    struct {
> +        struct xc_sr_ihdr ihdr;
> +        struct xc_sr_dhdr dhdr;
> +    } hdrs = {
> +        {
> +            .marker  = IHDR_MARKER,
> +            .id      = htonl(IHDR_ID),
> +            .version = htonl(3),
> +            .options = htons(IHDR_OPT_LITTLE_ENDIAN),
> +        },
> +        {
> +            .type       = guest_type,
> +            .page_shift = XC_PAGE_SHIFT,
> +            .xen_major  = (xen_version >> 16) & 0xffff,

You don't strictly need the mask here AFAICT?

Thanks, Roger.