[bpf-next,v3,5/7] bpf: add MAP_LOOKUP_AND_DELETE_ELEM syscall

The previous patch implemented a bpf queue/stack maps that
provided the peek/pop/push functions.  There is not a direct
relationship between those functions and the current maps
syscalls, hence a new MAP_LOOKUP_AND_DELETE_ELEM syscall is added,
this is mapped to the pop operation in the queue/stack maps
and it is still to implement in other kind of maps.

Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>
---
 include/uapi/linux/bpf.h |    1 +
 kernel/bpf/syscall.c     |   66 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

On Thu, Oct 18, 2018 at 6:16 AM Mauricio Vasquez B
<mauricio.vasquez@polito.it> wrote:
>
> The previous patch implemented a bpf queue/stack maps that
> provided the peek/pop/push functions.  There is not a direct
> relationship between those functions and the current maps
> syscalls, hence a new MAP_LOOKUP_AND_DELETE_ELEM syscall is added,
> this is mapped to the pop operation in the queue/stack maps
> and it is still to implement in other kind of maps.
>
> Signed-off-by: Mauricio Vasquez B <mauricio.vasquez@polito.it>

Acked-by: Song Liu <songliubraving@fb.com>

> ---
>  include/uapi/linux/bpf.h |    1 +
>  kernel/bpf/syscall.c     |   66 ++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 67 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index b8fc161c5b78..c8824d5364ff 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -103,6 +103,7 @@ enum bpf_cmd {
>         BPF_BTF_LOAD,
>         BPF_BTF_GET_FD_BY_ID,
>         BPF_TASK_FD_QUERY,
> +       BPF_MAP_LOOKUP_AND_DELETE_ELEM,
>  };
>
>  enum bpf_map_type {
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 1617407f9ee5..49ae64a26562 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -999,6 +999,69 @@ static int map_get_next_key(union bpf_attr *attr)
>         return err;
>  }
>
> +#define BPF_MAP_LOOKUP_AND_DELETE_ELEM_LAST_FIELD value
> +
> +static int map_lookup_and_delete_elem(union bpf_attr *attr)
> +{
> +       void __user *ukey = u64_to_user_ptr(attr->key);
> +       void __user *uvalue = u64_to_user_ptr(attr->value);
> +       int ufd = attr->map_fd;
> +       struct bpf_map *map;
> +       void *key, *value, *ptr;
> +       u32 value_size;
> +       struct fd f;
> +       int err;
> +
> +       if (CHECK_ATTR(BPF_MAP_LOOKUP_AND_DELETE_ELEM))
> +               return -EINVAL;
> +
> +       f = fdget(ufd);
> +       map = __bpf_map_get(f);
> +       if (IS_ERR(map))
> +               return PTR_ERR(map);
> +
> +       if (!(f.file->f_mode & FMODE_CAN_WRITE)) {
> +               err = -EPERM;
> +               goto err_put;
> +       }
> +
> +       key = __bpf_copy_key(ukey, map->key_size);
> +       if (IS_ERR(key)) {
> +               err = PTR_ERR(key);
> +               goto err_put;
> +       }
> +
> +       value_size = map->value_size;
> +
> +       err = -ENOMEM;
> +       value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
> +       if (!value)
> +               goto free_key;
> +
> +       if (map->map_type == BPF_MAP_TYPE_QUEUE ||
> +           map->map_type == BPF_MAP_TYPE_STACK) {
> +               err = map->ops->map_pop_elem(map, value);
> +       } else {
> +               err = -ENOTSUPP;
> +       }
> +
> +       if (err)
> +               goto free_value;
> +
> +       if (copy_to_user(uvalue, value, value_size) != 0)
> +               goto free_value;
> +
> +       err = 0;
> +
> +free_value:
> +       kfree(value);
> +free_key:
> +       kfree(key);
> +err_put:
> +       fdput(f);
> +       return err;
> +}
> +
>  static const struct bpf_prog_ops * const bpf_prog_types[] = {
>  #define BPF_PROG_TYPE(_id, _name) \
>         [_id] = & _name ## _prog_ops,
> @@ -2472,6 +2535,9 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz
>         case BPF_TASK_FD_QUERY:
>                 err = bpf_task_fd_query(&attr, uattr);
>                 break;
> +       case BPF_MAP_LOOKUP_AND_DELETE_ELEM:
> +               err = map_lookup_and_delete_elem(&attr);
> +               break;
>         default:
>                 err = -EINVAL;
>                 break;
>