Commit 281920b7 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Alexei Starovoitov
Browse files

bpf: Devmap adjust uapi for attach bpf program 



V2:
- Defer changing BPF-syscall to start at file-descriptor 1
- Use {} to zero initialise struct.

The recent commit fbee97fe ("bpf: Add support to attach bpf program to a
devmap entry"), introduced ability to attach (and run) a separate XDP
bpf_prog for each devmap entry. A bpf_prog is added via a file-descriptor.
As zero were a valid FD, not using the feature requires using value minus-1.
The UAPI is extended via tail-extending struct bpf_devmap_val and using
map->value_size to determine the feature set.

This will break older userspace applications not using the bpf_prog feature.
Consider an old userspace app that is compiled against newer kernel
uapi/bpf.h, it will not know that it need to initialise the member
bpf_prog.fd to minus-1. Thus, users will be forced to update source code to
get program running on newer kernels.

This patch remove the minus-1 checks, and have zero mean feature isn't used.

Followup patches either for kernel or libbpf should handle and avoid
returning file-descriptor zero in the first place.

Fixes: fbee97fe ("bpf: Add support to attach bpf program to a devmap entry")
Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/159170950687.2102545.7235914718298050113.stgit@firesoul
parent 248e00ac

include/uapi/linux/bpf.h

+13 −0
Original line number Diff line number Diff line
@@ -3761,6 +3761,19 @@ struct xdp_md { 
	__u32 egress_ifindex;  /* txq->dev->ifindex */

};



/* DEVMAP map-value layout

 *

 * The struct data-layout of map-value is a configuration interface.

 * New members can only be added to the end of this structure.

 */

struct bpf_devmap_val {

	__u32 ifindex;   /* device index */

	union {

		int   fd;  /* prog fd on map write */

		__u32 id;  /* prog id on map read */

	} bpf_prog;

};



enum sk_action {

	SK_DROP = 0,

	SK_PASS,

kernel/bpf/devmap.c

+4 −13
Original line number Diff line number Diff line
@@ -60,15 +60,6 @@ struct xdp_dev_bulk_queue { 
	unsigned int count;

};



/* DEVMAP values */

struct bpf_devmap_val {

	u32 ifindex;   /* device index */

	union {

		int fd;  /* prog fd on map write */

		u32 id;  /* prog id on map read */

	} bpf_prog;

};



struct bpf_dtab_netdev {

	struct net_device *dev; /* must be first member, due to tracepoint */

	struct hlist_node index_hlist;
@@ -619,7 +610,7 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net, 
	if (!dev->dev)

		goto err_out;



	if (val->bpf_prog.fd >= 0) {

	if (val->bpf_prog.fd > 0) {

		prog = bpf_prog_get_type_dev(val->bpf_prog.fd,

					     BPF_PROG_TYPE_XDP, false);

		if (IS_ERR(prog))
@@ -653,8 +644,8 @@ static int __dev_map_update_elem(struct net *net, struct bpf_map *map, 
				 void *key, void *value, u64 map_flags)

{

	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);

	struct bpf_devmap_val val = { .bpf_prog.fd = -1 };

	struct bpf_dtab_netdev *dev, *old_dev;

	struct bpf_devmap_val val = {};

	u32 i = *(u32 *)key;



	if (unlikely(map_flags > BPF_EXIST))
@@ -670,7 +661,7 @@ static int __dev_map_update_elem(struct net *net, struct bpf_map *map, 
	if (!val.ifindex) {

		dev = NULL;

		/* can not specify fd if ifindex is 0 */

		if (val.bpf_prog.fd != -1)

		if (val.bpf_prog.fd > 0)

			return -EINVAL;

	} else {

		dev = __dev_map_alloc_node(net, dtab, &val, i);
@@ -700,8 +691,8 @@ static int __dev_map_hash_update_elem(struct net *net, struct bpf_map *map, 
				     void *key, void *value, u64 map_flags)

{

	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);

	struct bpf_devmap_val val = { .bpf_prog.fd = -1 };

	struct bpf_dtab_netdev *dev, *old_dev;

	struct bpf_devmap_val val = {};

	u32 idx = *(u32 *)key;

	unsigned long flags;

	int err = -EEXIST;

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