Re: [PATCH Remus v2 02/10] tools/libxc: introduce setup() and cleanup() on save

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 08/05/15 10:33, Yang Hongyang wrote:
> introduce setup() and cleanup() which subsume the
> ctx->save.ops.{setup,cleanup}() calls and also do allocate/free
> necessary memory.
> The SHADOW_OP_OFF hypercall also included in the cleanup().
>
> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>

I would suggest swapping this with patch 1, to save introducing new
code, just to move it again in the next patch.

In general, a good change, but some comments...

> ---
>  tools/libxc/xc_sr_save.c | 72 +++++++++++++++++++++++++++++-------------------
>  1 file changed, 44 insertions(+), 28 deletions(-)
>
> diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
> index cc3e6b1..2394bc4 100644
> --- a/tools/libxc/xc_sr_save.c
> +++ b/tools/libxc/xc_sr_save.c
> @@ -607,13 +607,10 @@ static int send_domain_memory_nonlive(struct xc_sr_context *ctx)
>      return rc;
>  }
>  
> -/*
> - * Save a domain.
> - */
> -static int save(struct xc_sr_context *ctx, uint16_t guest_type)
> +static int setup(struct xc_sr_context *ctx)
>  {
>      xc_interface *xch = ctx->xch;
> -    int rc, saved_rc = 0, saved_errno = 0;
> +    int rc;
>      DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap,
>                                      (&ctx->save.dirty_bitmap_hbuf));
>  
> @@ -632,13 +629,51 @@ static int save(struct xc_sr_context *ctx, uint16_t guest_type)
>          goto err;
>      }
>  
> -    IPRINTF("Saving domain %d, type %s",
> -            ctx->domid, dhdr_type_to_str(guest_type));
> -
>      rc = ctx->save.ops.setup(ctx);
>      if ( rc )
>          goto err;
>  
> +    rc = 0;
> +
> + err:
> +    return rc;
> +
> +}
> +
> +static void cleanup(struct xc_sr_context *ctx)
> +{
> +    xc_interface *xch = ctx->xch;
> +    DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap,
> +                                    (&ctx->save.dirty_bitmap_hbuf));
> +
> +    xc_shadow_control(xch, ctx->domid, XEN_DOMCTL_SHADOW_OP_OFF,
> +                      NULL, 0, NULL, 0, NULL);
> +
> +    if ( ctx->save.ops.cleanup(ctx) )
> +        PERROR("Failed to clean up");
> +
> +    if ( dirty_bitmap )
> +        xc_hypercall_buffer_free_pages(xch, dirty_bitmap,
> +                                   NRPAGES(bitmap_size(ctx->save.p2m_size)));

xc_hypercall_buffer_free_pages() if fine dealing with NULL, just like
free() is.  You can drop the conditional.

> +    free(ctx->save.deferred_pages);
> +    free(ctx->save.batch_pfns);
> +}
> +
> +/*
> + * Save a domain.
> + */
> +static int save(struct xc_sr_context *ctx, uint16_t guest_type)
> +{
> +    xc_interface *xch = ctx->xch;
> +    int rc;
> +
> +    rc = setup(ctx);
> +    if ( rc )
> +        goto err;
> +
> +    IPRINTF("Saving domain %d, type %s",
> +            ctx->domid, dhdr_type_to_str(guest_type));
> +
>      xc_report_progress_single(xch, "Start of stream");
>  
>      rc = write_headers(ctx, guest_type);
> @@ -679,29 +714,10 @@ static int save(struct xc_sr_context *ctx, uint16_t guest_type)
>      goto done;
>  
>   err:
> -    saved_errno = errno;
> -    saved_rc = rc;
>      PERROR("Save failed");
>  
>   done:
> -    xc_shadow_control(xch, ctx->domid, XEN_DOMCTL_SHADOW_OP_OFF,
> -                      NULL, 0, NULL, 0, NULL);
> -
> -    rc = ctx->save.ops.cleanup(ctx);
> -    if ( rc )
> -        PERROR("Failed to clean up");
> -
> -    xc_hypercall_buffer_free_pages(xch, dirty_bitmap,
> -                                   NRPAGES(bitmap_size(ctx->save.p2m_size)));
> -    free(ctx->save.deferred_pages);
> -    free(ctx->save.batch_pfns);
> -
> -    if ( saved_rc )
> -    {
> -        rc = saved_rc;
> -        errno = saved_errno;
> -    }

You must keep saved_{rc,errno}, so that the cleanup doesn't clobber the
errno semantically relevant to why the save failed.

~Andrew

> -
> +    cleanup(ctx);
>      return rc;
>  };
>