Re: [PATCH] libxl: Rewind toolstack_save_fd in libxl_save_helper when using remus

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

On 20/06/14 07:59, Yang Hongyang wrote:
> commit(b327a3f421bb57d262b7d1fb3c43b710852b103b) move the rewinding
> of toolstack_save_fd to libxl, this breaks remus, because in remus
> mode, toolstack_save_cb will be called in every checkpoint, if
> we don't rewind it in libxl_save_helper, it will surely encounted
> error.
>
> I know this fix is just a hack, in fact the whole toolstack save
> thing should be done in libxl. But this fix should solve Jason's
> case and remus thing. Until migration v2 is upstreamed, this fix
> should be fine.
>
> Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
> CC: Jason Andryuk <andryuk@aero.org>
> CC: Andrew Cooper <andrew.cooper3@citrix.com>
> CC: Ian Jackson <ian.jackson@eu.citrix.com>

Hmm - this is very hacky, but I don't see an alternative.

As b327a3f421 did regress remus, this fix should be taken.  It will only
be temporary until the libxl layering violation fixes from migration v2
appear.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>


> ---
>  tools/libxl/libxl_save_helper.c |    8 +++++++-
>  1 files changed, 7 insertions(+), 1 deletions(-)
>
> diff --git a/tools/libxl/libxl_save_helper.c b/tools/libxl/libxl_save_helper.c
> index b259bd0..4619fa3 100644
> --- a/tools/libxl/libxl_save_helper.c
> +++ b/tools/libxl/libxl_save_helper.c
> @@ -159,6 +159,7 @@ int helper_getreply(void *user)
>  
>  static int toolstack_save_fd;
>  static uint32_t toolstack_save_len;
> +static struct save_callbacks helper_save_callbacks;
>  
>  static int toolstack_save_cb(uint32_t domid, uint8_t **buf,
>                               uint32_t *len, void *data)
> @@ -167,6 +168,12 @@ static int toolstack_save_cb(uint32_t domid, uint8_t **buf,
>  
>      assert(toolstack_save_fd > 0);
>  
> +    /* This is a hack for remus */
> +    if (helper_save_callbacks.checkpoint) {
> +        r = lseek(toolstack_save_fd, 0, SEEK_SET);
> +        if (r) fail(errno,"rewind toolstack data tmpfile");
> +    }
> +
>      *buf = xmalloc(toolstack_save_len);
>      r = read_exactly(toolstack_save_fd, *buf, toolstack_save_len);
>      if (r<0) fail(errno,"read toolstack data");
> @@ -191,7 +198,6 @@ static void complete(int retval) {
>      exit(0);
>  }
>  
> -static struct save_callbacks helper_save_callbacks;
>  static struct restore_callbacks helper_restore_callbacks;
>  
>  int main(int argc, char **argv)