libbpf: fix errno is overwritten after being closed.

In the ensure_good_fd function, if the fcntl function succeeds but
the close function fails, ensure_good_fd returns a normal fd and
sets errno, which may cause users to misunderstand. The close
failure is not a serious problem, and the correct FD has been
handed over to the upper-layer application. Let's restore errno here.

Signed-off-by: Xin Liu <liuxin350@huawei.com>
Link: https://lore.kernel.org/r/20221223133618.10323-1-liuxin350@huawei.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index 377642f..98333a6 100644 (file)
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h
@@ -543,10 +543,9 @@ static inline int ensure_good_fd(int fd)
                fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
                saved_errno = errno;
                close(old_fd);
-               if (fd < 0) {
+               errno = saved_errno;
+               if (fd < 0)
                        pr_warn("failed to dup FD %d to FD > 2: %d\n", old_fd, -saved_errno);
-                       errno = saved_errno;
-               }
        }
        return fd;
 }