Re: [Qemu-devel] [PATCH 1/2] Add TAILQ_FOREACH_SAFE

[Anthony Liguori <anthony@codemonkey.ws>]

Jan Kiszka wrote:
> Add TAILQ iterator that allows to safely remove elements while walking
> the list.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>
>  sys-queue.h |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/sys-queue.h b/sys-queue.h
> index 3d0773e..b92a77f 100644
> --- a/sys-queue.h
> +++ b/sys-queue.h
> @@ -210,6 +210,12 @@ struct {                                                                \
>                  (var);                                                  \
>                  (var) = ((var)->field.tqe_next))
>  
> +#define TAILQ_FOREACH_SAFE(var, head, field, next_var)                  \
> +        for ((var) = ((head)->tqh_first);                               \
> +                (var) ? ({ (next_var) = ((var)->field.tqe_next); 1; })  \
> +                      : 0;                                              \
> +                (var) = (next_var))
>   

So the Linux implementation of this is:

#define list_for_each_safe(pos, n, head) \
    for (pos = (head)->next, n = pos->next; pos != (head); \
        pos = n, n = pos->next)

I'd prefer something similar:

#define TAILQ_FOREACH_SAFE(var, head, field, next_var)
             for (var = (head)->tqh_first, next_var = var->field.tqe_next;
                   var;
                   var = next_var, next_var = var->field.tqe_next)

As it's functionally equivalent and avoids using a GCC-ism ({}).

Regards,

Anthony Liguori