Re: [PATCH v3 bpf-next 2/2] libbpf: remove qidconf and better support external bpf programs.

[Jonathan Lemon]

On 1 Jun 2019, at 16:05, Song Liu wrote:

On May 31, 2019, at 11:57 AM, Jonathan Lemon 
<jonathan.le...@gmail.com> wrote:

Use the recent change to XSKMAP bpf_map_lookup_elem() to test if
there is a xsk present in the map instead of duplicating the work
with qidconf.

Fix things so callers using XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD
bypass any internal bpf maps, so xsk_socket__{create|delete} works
properly.

Signed-off-by: Jonathan Lemon <jonathan.le...@gmail.com>
---
tools/lib/bpf/xsk.c | 79 
+++++++++------------------------------------
1 file changed, 16 insertions(+), 63 deletions(-)

diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
index 38667b62f1fe..7ce7494b5b50 100644
--- a/tools/lib/bpf/xsk.c
+++ b/tools/lib/bpf/xsk.c
@@ -60,10 +60,8 @@ struct xsk_socket {
        struct xsk_umem *umem;
        struct xsk_socket_config config;
        int fd;
-       int xsks_map;
        int ifindex;
        int prog_fd;
-       int qidconf_map_fd;
        int xsks_map_fd;
        __u32 queue_id;
        char ifname[IFNAMSIZ];
@@ -265,15 +263,11 @@ static int xsk_load_xdp_prog(struct xsk_socket 
*xsk)
        /* This is the C-program:
         * SEC("xdp_sock") int xdp_sock_prog(struct xdp_md *ctx)
         * {
-        *     int *qidconf, index = ctx->rx_queue_index;
+        *     int index = ctx->rx_queue_index;
         *
         *     // A set entry here means that the correspnding queue_id
         *     // has an active AF_XDP socket bound to it.
-        *     qidconf = bpf_map_lookup_elem(&qidconf_map, &index);
-        *     if (!qidconf)
-        *         return XDP_ABORTED;
-        *
-        *     if (*qidconf)
+        *     if (bpf_map_lookup_elem(&xsks_map, &index))
         *         return bpf_redirect_map(&xsks_map, index, 0);
         *
         *     return XDP_PASS;
@@ -286,15 +280,10 @@ static int xsk_load_xdp_prog(struct xsk_socket 
*xsk)
                BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_1, -4),
                BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
                BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4),
-               BPF_LD_MAP_FD(BPF_REG_1, xsk->qidconf_map_fd),
+               BPF_LD_MAP_FD(BPF_REG_1, xsk->xsks_map_fd),
                BPF_EMIT_CALL(BPF_FUNC_map_lookup_elem),
                BPF_MOV64_REG(BPF_REG_1, BPF_REG_0),
-               BPF_MOV32_IMM(BPF_REG_0, 0),
-               /* if r1 == 0 goto +8 */
-               BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 8),
                BPF_MOV32_IMM(BPF_REG_0, 2),
-               /* r1 = *(u32 *)(r1 + 0) */
-               BPF_LDX_MEM(BPF_W, BPF_REG_1, BPF_REG_1, 0),
                /* if r1 == 0 goto +5 */
                BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 5),
                /* r2 = *(u32 *)(r10 - 4) */
@@ -366,18 +355,11 @@ static int xsk_create_bpf_maps(struct 
xsk_socket *xsk)
        if (max_queues < 0)
                return max_queues;

-       fd = bpf_create_map_name(BPF_MAP_TYPE_ARRAY, "qidconf_map",
+       fd = bpf_create_map_name(BPF_MAP_TYPE_XSKMAP, "xsks_map",
                                 sizeof(int), sizeof(int), max_queues, 0);
        if (fd < 0)
                return fd;
-       xsk->qidconf_map_fd = fd;

-       fd = bpf_create_map_name(BPF_MAP_TYPE_XSKMAP, "xsks_map",
-                                sizeof(int), sizeof(int), max_queues, 0);
-       if (fd < 0) {
-               close(xsk->qidconf_map_fd);
-               return fd;
-       }
        xsk->xsks_map_fd = fd;

        return 0;
@@ -385,10 +367,8 @@ static int xsk_create_bpf_maps(struct xsk_socket 
*xsk)

static void xsk_delete_bpf_maps(struct xsk_socket *xsk)
{
-       close(xsk->qidconf_map_fd);
+       bpf_map_delete_elem(xsk->xsks_map_fd, &xsk->queue_id);
        close(xsk->xsks_map_fd);
-       xsk->qidconf_map_fd = -1;
-       xsk->xsks_map_fd = -1;
}

static int xsk_lookup_bpf_maps(struct xsk_socket *xsk)
@@ -417,10 +397,9 @@ static int xsk_lookup_bpf_maps(struct xsk_socket 
*xsk)
        if (err)
                goto out_map_ids;

-       for (i = 0; i < prog_info.nr_map_ids; i++) {
-               if (xsk->qidconf_map_fd != -1 && xsk->xsks_map_fd != -1)
-                       break;
+       xsk->xsks_map_fd = -1;

+       for (i = 0; i < prog_info.nr_map_ids; i++) {
                fd = bpf_map_get_fd_by_id(map_ids[i]);
                if (fd < 0)
                        continue;
@@ -431,11 +410,6 @@ static int xsk_lookup_bpf_maps(struct xsk_socket 
*xsk)
                        continue;
                }

-               if (!strcmp(map_info.name, "qidconf_map")) {
-                       xsk->qidconf_map_fd = fd;
-                       continue;
-               }
-
                if (!strcmp(map_info.name, "xsks_map")) {
                        xsk->xsks_map_fd = fd;
                        continue;
@@ -445,40 +419,18 @@ static int xsk_lookup_bpf_maps(struct 
xsk_socket *xsk)
        }

        err = 0;
-       if (xsk->qidconf_map_fd < 0 || xsk->xsks_map_fd < 0) {
+       if (xsk->xsks_map_fd == -1)
                err = -ENOENT;
-               xsk_delete_bpf_maps(xsk);
-       }

out_map_ids:
        free(map_ids);
        return err;
}

-static void xsk_clear_bpf_maps(struct xsk_socket *xsk)
-{
-       int qid = false;
-
-       bpf_map_update_elem(xsk->qidconf_map_fd, &xsk->queue_id, &qid, 0);
-       bpf_map_delete_elem(xsk->xsks_map_fd, &xsk->queue_id);
-}
-
static int xsk_set_bpf_maps(struct xsk_socket *xsk)
{
-       int qid = true, fd = xsk->fd, err;
-
-	err = bpf_map_update_elem(xsk->qidconf_map_fd, &xsk->queue_id, 
&qid, 0);
-       if (err)
-               goto out;
-
-	err = bpf_map_update_elem(xsk->xsks_map_fd, &xsk->queue_id, &fd, 
0);
-       if (err)
-               goto out;
-
-       return 0;
-out:
-       xsk_clear_bpf_maps(xsk);
-       return err;
+       return bpf_map_update_elem(xsk->xsks_map_fd, &xsk->queue_id,
+                                  &xsk->fd, 0);
}

static int xsk_setup_xdp_prog(struct xsk_socket *xsk)
@@ -514,6 +466,7 @@ static int xsk_setup_xdp_prog(struct xsk_socket 
*xsk)

out_load:
        close(xsk->prog_fd);
+       xsk->prog_fd = -1;

I found xsk->prog_fd confusing. Why do we need to set it here?

I suppose this one isn't strictly required - I set it as a guard out of 
habit.
xsk is (currently) immediately freed by the caller, so it can be 
removed.


The main logic is:

        xsk->prog_fd = -1;
        if (!(xsk->config.libbpf_flags & 
XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD)) {
                err = xsk_setup_xdp_prog(xsk);

The user may pass INHIBIT_PROG_LOAD, which bypasses setting up the xdp 
program
(and any maps associated with the program), allowing installation of a 
custom
program.  The cleanup behavior is then gated on prog_fd being -1,


I think we don't need to call xsk_delete_bpf_maps() in out_load path?

Hmm, there's two out_load paths, but only one needs the delete maps 
call.  Let
me redo the error handling so it's a bit more explicit.



out_maps:
        xsk_delete_bpf_maps(xsk);
        return err;
@@ -643,9 +596,7 @@ int xsk_socket__create(struct xsk_socket 
**xsk_ptr, const char *ifname,
                goto out_mmap_tx;
        }

-       xsk->qidconf_map_fd = -1;
-       xsk->xsks_map_fd = -1;
-
+       xsk->prog_fd = -1;
	if (!(xsk->config.libbpf_flags & 
XSK_LIBBPF_FLAGS__INHIBIT_PROG_LOAD)) {
                err = xsk_setup_xdp_prog(xsk);
                if (err)
@@ -708,8 +659,10 @@ void xsk_socket__delete(struct xsk_socket *xsk)
        if (!xsk)
                return;

-       xsk_clear_bpf_maps(xsk);
-       xsk_delete_bpf_maps(xsk);
+       if (xsk->prog_fd != -1) {
+               xsk_delete_bpf_maps(xsk);
+               close(xsk->prog_fd);

Here, we use prog_fd != -1 to gate xsk_delete_bpf_maps(), which is
confusing. I looked at the code for quite sometime, but still cannot
confirm it is correct.

See above reasoning - with INHIBIT_PROG_LOAD, there is no 
library-provided
program or maps, so cleanup actions are skipped.
--
Jonathan