答复: [PATCH v4,bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd
From: shaozhengchao <hidden>
Date: 2022-06-01 10:33:50
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bpf, lkml
-----邮件原件----- 发件人: Toke Høiland-Jørgensen [mailto:toke@kernel.org] 发送时间: 2022年6月1日 17:25 收件人: shaozhengchao [off-list ref]; bpf@vger.kernel.org; netdev@vger.kernel.org; linux-kernel@vger.kernel.org; ast@kernel.org; daniel@iogearbox.net; davem@davemloft.net; kuba@kernel.org; hawk@kernel.org; john.fastabend@gmail.com; andrii@kernel.org; kafai@fb.com; songliubraving@fb.com; yhs@fb.com; kpsingh@kernel.org 抄送: weiyongjun (A) [off-list ref]; shaozhengchao [off-list ref]; yuehaibing [off-list ref] 主题: Re: [PATCH v4,bpf-next] samples/bpf: check detach prog exist or not in xdp_fwd Zhengchao Shao [off-list ref] writes:
Before detach the prog, we should check detach prog exist or not. Signed-off-by: Zhengchao Shao <redacted>
The logic looks good now, just spotted one issue with the use of 'return errno' (which I just realised I suggested on the last version, sorry about that).
quoted hunk ↗ jump to hunk
samples/bpf/xdp_fwd_user.c | 62 ++++++++++++++++++++++++++++++++------ 1 file changed, 53 insertions(+), 9 deletions(-)diff --git a/samples/bpf/xdp_fwd_user.c b/samples/bpf/xdp_fwd_user.c index 1828487bae9a..a4ba53891653 100644 --- a/samples/bpf/xdp_fwd_user.c +++ b/samples/bpf/xdp_fwd_user.c@@ -47,17 +47,61 @@ static int do_attach(int idx, int prog_fd, int map_fd, const char *name) return err; } -static int do_detach(int idx, const char *name) +static int do_detach(int ifindex, const char *ifname, const char +*app_name) { - int err; + LIBBPF_OPTS(bpf_xdp_attach_opts, opts); + struct bpf_prog_info prog_info = {}; + char prog_name[BPF_OBJ_NAME_LEN]; + __u32 info_len, curr_prog_id; + int prog_fd; + int err = 1; + + if (bpf_xdp_query_id(ifindex, xdp_flags, &curr_prog_id)) { + printf("ERROR: bpf_xdp_query_id failed (%s)\n", + strerror(errno)); + return -errno;
The printf above may override errno, so this could return 0; the actual return value is not really used by the caller, so you could just always 'return -1' or 'return err'.
+ }
+
+ if (!curr_prog_id) {
+ printf("ERROR: flags(0x%x) xdp prog is not attached to %s\n",
+ xdp_flags, ifname);
+ goto err_out;Doesn't really need a label, just do a direct return here as well.
+ }
- err = bpf_xdp_detach(idx, xdp_flags, NULL);
- if (err < 0)
- printf("ERROR: failed to detach program from %s\n", name);
+ info_len = sizeof(prog_info);
+ prog_fd = bpf_prog_get_fd_by_id(curr_prog_id);
+ if (prog_fd < 0) {
+ printf("ERROR: bpf_prog_get_fd_by_id failed (%s)\n",
+ strerror(errno));
+ return -errno;Same issue as above with errno being overwritten.
+ }
+
+ err = bpf_obj_get_info_by_fd(prog_fd, &prog_info, &info_len);
+ if (err) {
+ printf("ERROR: bpf_obj_get_info_by_fd failed (%s)\n",
+ strerror(errno));
+ goto close_out;
+ }
+ snprintf(prog_name, sizeof(prog_name), "%s_prog", app_name);
+ prog_name[BPF_OBJ_NAME_LEN - 1] = '\0';
+
+ if (strcmp(prog_info.name, prog_name)) {
+ printf("ERROR: %s isn't attached to %s\n", app_name, ifname);
+ err = 1;
+ } else {You can save a level of indentation by adding a 'goto close_out' after 'err=1' instead of using an 'else' block.
+ opts.old_prog_fd = prog_fd;
+ err = bpf_xdp_detach(ifindex, xdp_flags, &opts);
+ if (err < 0)
+ printf("ERROR: failed to detach program from %s (%s)\n",
+ ifname, strerror(errno));
+ /* TODO: Remember to cleanup map, when adding use of shared map
+ * bpf_map_delete_elem((map_fd, &idx);
+ */
+ }
- /* TODO: Remember to cleanup map, when adding use of shared map
- * bpf_map_delete_elem((map_fd, &idx);
- */
+close_out:
+ close(prog_fd);
+err_out:don't need the err_out label, see above. -Toke Hi Toke: Thank you for your reply. I will fix it in next patch. Zhengchao Shao