[PATCH bpf-next] bpf: libbpf: retry map creation without the name

[PATCH bpf-next] bpf: libbpf: retry map creation without the name

[Stanislav Fomichev]

Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
for maps. Pre v4.14 kernels don't know about map names and return an
error about unexpected non-zero data. Retry sys_bpf without a map
name to cover older kernels.

Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 tools/lib/bpf/bpf.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 03f9bcc4ef50..673175bc06ee 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,7 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 {
 	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
 	union bpf_attr attr;
+	int ret;
 
 	memset(&attr, '\0', sizeof(attr));
 
@@ -86,7 +87,15 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 	attr.map_ifindex = create_attr->map_ifindex;
 	attr.inner_map_fd = create_attr->inner_map_fd;
 
-	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	ret = sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	if (ret < 0 && create_attr->name) {
+		/* Retry the same syscall, but without the name.
+		 * Pre v4.14 kernels don't support map names.
+		 */
+		memset(attr.map_name, 0, sizeof(attr.map_name));
+		return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	}
+	return ret;
 }
 
 int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
-- 
2.19.1.1215.g8438c0b245-goog

Re: [PATCH bpf-next] bpf: libbpf: retry map creation without the name

[Daniel Borkmann]

On 11/19/2018 10:35 PM, Stanislav Fomichev wrote:
> Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
> to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
> for maps. Pre v4.14 kernels don't know about map names and return an
> error about unexpected non-zero data. Retry sys_bpf without a map
> name to cover older kernels.

Looks good, small nit below:

> Signed-off-by: Stanislav Fomichev <sdf@google.com>
> ---
>  tools/lib/bpf/bpf.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index 03f9bcc4ef50..673175bc06ee 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -69,6 +69,7 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
>  {
>  	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
>  	union bpf_attr attr;
> +	int ret;
>  
>  	memset(&attr, '\0', sizeof(attr));
>  
> @@ -86,7 +87,15 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
>  	attr.map_ifindex = create_attr->map_ifindex;
>  	attr.inner_map_fd = create_attr->inner_map_fd;
>  
> -	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
> +	ret = sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
> +	if (ret < 0 && create_attr->name) {

Could you also check errno being EINVAL here so that we do not try to
confuse it with an error coming from insufficient memlock which is
EPERM in that case.

> +		/* Retry the same syscall, but without the name.
> +		 * Pre v4.14 kernels don't support map names.
> +		 */
> +		memset(attr.map_name, 0, sizeof(attr.map_name));
> +		return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
> +	}
> +	return ret;
>  }
>  
>  int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
> 

[PATCH bpf-next v2] bpf: libbpf: retry map creation without the name

[Stanislav Fomichev]

Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
for maps. Pre v4.14 kernels don't know about map names and return an
error about unexpected non-zero data. Retry sys_bpf without a map
name to cover older kernels.

v2 changes:
* check for errno == EINVAL as suggested by Daniel Borkmann

Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 tools/lib/bpf/bpf.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
index 03f9bcc4ef50..961e1b9fc592 100644
--- a/tools/lib/bpf/bpf.c
+++ b/tools/lib/bpf/bpf.c
@@ -69,6 +69,7 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 {
 	__u32 name_len = create_attr->name ? strlen(create_attr->name) : 0;
 	union bpf_attr attr;
+	int ret;
 
 	memset(&attr, '\0', sizeof(attr));
 
@@ -86,7 +87,15 @@ int bpf_create_map_xattr(const struct bpf_create_map_attr *create_attr)
 	attr.map_ifindex = create_attr->map_ifindex;
 	attr.inner_map_fd = create_attr->inner_map_fd;
 
-	return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	ret = sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	if (ret < 0 && errno == EINVAL && create_attr->name) {
+		/* Retry the same syscall, but without the name.
+		 * Pre v4.14 kernels don't support map names.
+		 */
+		memset(attr.map_name, 0, sizeof(attr.map_name));
+		return sys_bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+	}
+	return ret;
 }
 
 int bpf_create_map_node(enum bpf_map_type map_type, const char *name,
-- 
2.19.1.1215.g8438c0b245-goog

Re: [PATCH bpf-next v2] bpf: libbpf: retry map creation without the name

[Daniel Borkmann]

On 11/19/2018 11:49 PM, Stanislav Fomichev wrote:
> Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
> to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
> for maps. Pre v4.14 kernels don't know about map names and return an
> error about unexpected non-zero data. Retry sys_bpf without a map
> name to cover older kernels.
> 
> v2 changes:
> * check for errno == EINVAL as suggested by Daniel Borkmann
> 
> Signed-off-by: Stanislav Fomichev <sdf@google.com>

Applied to bpf-next, thanks!

Re: [PATCH bpf-next v2] bpf: libbpf: retry map creation without the name

[Stanislav Fomichev]

On 11/20, Daniel Borkmann wrote:
> On 11/19/2018 11:49 PM, Stanislav Fomichev wrote:
> > Since commit 88cda1c9da02 ("bpf: libbpf: Provide basic API support
> > to specify BPF obj name"), libbpf unconditionally sets bpf_attr->name
> > for maps. Pre v4.14 kernels don't know about map names and return an
> > error about unexpected non-zero data. Retry sys_bpf without a map
> > name to cover older kernels.
> > 
> > v2 changes:
> > * check for errno == EINVAL as suggested by Daniel Borkmann
> > 
> > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> 
> Applied to bpf-next, thanks!
Great, thanks! It looks like there might be the same problem with the
program's name. I'll probably follow up with another patch soon.