On 9/11/18 4:11 AM, Björn Töpel wrote:
Hi Yonghong, I tried to run the XDP samples from the bpf-next tip
today, and was hit by a regression.
Commit f7010770fbac ("tools/bpf: move bpf/lib netlink related
functions into a new file") adds a while(1) around the recv call in
bpf_set_link_xdp_fd making that call getting stuck in an infinite
loop.
I simply removed the loop, and that solved my problem (patch below).
However, I don't know if removing the loop would break bpftool for
you. If not, I can submit the patch as a proper one for bpf-next.
Hi, Björn, thanks for reporting the problem.
The while loop is needed since the "recv" syscall buffer size
may not be big enough to hold all the returned information, in
which cases, multiple "recv" calls are needed.
Could you try the following patch to see whether it fixed your
issue? Thanks!
commit 3eb1c0249dfc3ea4ad61aa223dce32262af7e049 (HEAD -> fix)
Author: Yonghong Song <y...@fb.com>
Date: Tue Sep 11 08:58:20 2018 -0700
tools/bpf: fix a netlink recv issue
Commit f7010770fbac ("tools/bpf: move bpf/lib netlink related
functions into a new file") introduced a while loop for the
netlink recv path. This while loop is needed since the
buffer in recv syscall may not be big enough to hold all the
information and in such cases multiple recv calls are needed.
When netlink recv returns message length of 0, there will be
no more messages for returning data so the while loop
can end.
Fixes: f7010770fbac ("tools/bpf: move bpf/lib netlink related
functions into a new file")
Reported-by: Björn Töpel <bjorn.to...@intel.com>
Signed-off-by: Yonghong Song <y...@fb.com>
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 469e068dd0c5..37827319a50a 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -77,6 +77,9 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid,
int seq,
goto done;
}
+ if (len == 0)
+ break;
+
for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len);
nh = NLMSG_NEXT(nh, len)) {
if (nh->nlmsg_pid != nl_pid) {
Thanks!
Björn
From: =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <bjorn.to...@intel.com>
Date: Tue, 11 Sep 2018 12:35:44 +0200
Subject: [PATCH] tools/bpf: remove loop around netlink recv
Commit f7010770fbac ("tools/bpf: move bpf/lib netlink related
functions into a new file") moved the bpf_set_link_xdp_fd and split it
up into multiple functions. The added receive function
bpf_netlink_recv added a loop around the recv syscall leading to
multiple recv calls. This resulted in all XDP samples in the
samples/bpf/ to stop working, since they were stuck in a blocking
recv.
This commits removes the while (1)-statement.
Fixes: f7010770fbac ("tools/bpf: move bpf/lib netlink related
functions into a new file")
Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
---
tools/lib/bpf/netlink.c | 64 ++++++++++++++++++++---------------------
1 file changed, 31 insertions(+), 33 deletions(-)
diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
index 469e068dd0c5..0eae1fbf46c6 100644
--- a/tools/lib/bpf/netlink.c
+++ b/tools/lib/bpf/netlink.c
@@ -70,41 +70,39 @@ static int bpf_netlink_recv(int sock, __u32 nl_pid, int seq,
char buf[4096];
int len, ret;
- while (1) {
- len = recv(sock, buf, sizeof(buf), 0);
- if (len < 0) {
- ret = -errno;
+ len = recv(sock, buf, sizeof(buf), 0);
+ if (len < 0) {
+ ret = -errno;
+ goto done;
+ }
+
+ for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len);
+ nh = NLMSG_NEXT(nh, len)) {
+ if (nh->nlmsg_pid != nl_pid) {
+ ret = -LIBBPF_ERRNO__WRNGPID;
goto done;
}
-
- for (nh = (struct nlmsghdr *)buf; NLMSG_OK(nh, len);
- nh = NLMSG_NEXT(nh, len)) {
- if (nh->nlmsg_pid != nl_pid) {
- ret = -LIBBPF_ERRNO__WRNGPID;
- goto done;
- }
- if (nh->nlmsg_seq != seq) {
- ret = -LIBBPF_ERRNO__INVSEQ;
- goto done;
- }
- switch (nh->nlmsg_type) {
- case NLMSG_ERROR:
- err = (struct nlmsgerr *)NLMSG_DATA(nh);
- if (!err->error)
- continue;
- ret = err->error;
- nla_dump_errormsg(nh);
- goto done;
- case NLMSG_DONE:
- return 0;
- default:
- break;
- }
- if (_fn) {
- ret = _fn(nh, fn, cookie);
- if (ret)
- return ret;
- }
+ if (nh->nlmsg_seq != seq) {
+ ret = -LIBBPF_ERRNO__INVSEQ;
+ goto done;
+ }
+ switch (nh->nlmsg_type) {
+ case NLMSG_ERROR:
+ err = (struct nlmsgerr *)NLMSG_DATA(nh);
+ if (!err->error)
+ continue;
+ ret = err->error;
+ nla_dump_errormsg(nh);
+ goto done;
+ case NLMSG_DONE:
+ return 0;
+ default:
+ break;
+ }
+ if (_fn) {
+ ret = _fn(nh, fn, cookie);
+ if (ret)
+ return ret;
}
}
ret = 0;
