[PATCH bpf-next 1/6] bpf: error handling when map_lookup_elem isn't supported

[Prashant Bhole]

The error value returned by map_lookup_elem doesn't differentiate
whether lookup was failed because of invalid key or lookup is not
supported.

Lets add handling for -EOPNOTSUPP return value of map_lookup_elem()
method of map, with expectation from map's implementation that it
should return -EOPNOTSUPP if lookup is not supported.

The errno for bpf syscall for BPF_MAP_LOOKUP_ELEM command will be set
to EOPNOTSUPP if map lookup is not supported.

Signed-off-by: Prashant Bhole 
Acked-by: Alexei Starovoitov 
---
 kernel/bpf/syscall.c | 9 +++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5742df21598c..4f416234251f 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -719,10 +719,15 @@ static int map_lookup_elem(union bpf_attr *attr)
} else {
rcu_read_lock();
ptr = map->ops->map_lookup_elem(map, key);
-   if (ptr)
+   if (IS_ERR(ptr)) {
+   err = PTR_ERR(ptr);
+   } else if (!ptr) {
+   err = -ENOENT;
+   } else {
+   err = 0;
memcpy(value, ptr, value_size);
+   }
rcu_read_unlock();
-   err = ptr ? 0 : -ENOENT;
}
 
if (err)
-- 
2.17.1

Re: [PATCH bpf-next 1/6] bpf: error handling when map_lookup_elem isn't supported

[Song Liu]

On Mon, Oct 8, 2018 at 6:06 PM Prashant Bhole
 wrote:
>
> The error value returned by map_lookup_elem doesn't differentiate
> whether lookup was failed because of invalid key or lookup is not
> supported.
>
> Lets add handling for -EOPNOTSUPP return value of map_lookup_elem()
> method of map, with expectation from map's implementation that it
> should return -EOPNOTSUPP if lookup is not supported.
>
> The errno for bpf syscall for BPF_MAP_LOOKUP_ELEM command will be set
> to EOPNOTSUPP if map lookup is not supported.
>
> Signed-off-by: Prashant Bhole 
> Acked-by: Alexei Starovoitov 

Acked-by: Song Liu 

> ---
>  kernel/bpf/syscall.c | 9 +++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 5742df21598c..4f416234251f 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -719,10 +719,15 @@ static int map_lookup_elem(union bpf_attr *attr)
> } else {
> rcu_read_lock();
> ptr = map->ops->map_lookup_elem(map, key);
> -   if (ptr)
> +   if (IS_ERR(ptr)) {
> +   err = PTR_ERR(ptr);
> +   } else if (!ptr) {
> +   err = -ENOENT;
> +   } else {
> +   err = 0;
> memcpy(value, ptr, value_size);
> +   }
> rcu_read_unlock();
> -   err = ptr ? 0 : -ENOENT;
> }
>
> if (err)
> --
> 2.17.1
>
>