bpftool, musl compat: Replace nftw with FTW_ACTIONRETVAL

musl nftw implementation does not support FTW_ACTIONRETVAL. There have been
multiple attempts at pushing the feature in musl upstream, but it has been
refused or ignored all the times:

  https://www.openwall.com/lists/musl/2021/03/26/1
  https://www.openwall.com/lists/musl/2022/01/22/1

In this case we only care about /proc/<pid>/fd/<fd>, so it's not too difficult
to reimplement directly instead, and the new implementation makes 'bpftool perf'
slightly faster because it doesn't needlessly stat/readdir unneeded directories
(54ms -> 13ms on my machine).

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220424051022.2619648-4-asmadeus@codewreck.org

diff --git a/tools/bpf/bpftool/perf.c b/tools/bpf/bpftool/perf.c
index 50de087b0db72e529a3dbe693223664991423d4c..226ec2c39052401c76fa78f1d6fa6150ec1b6104 100644 (file)
--- a/tools/bpf/bpftool/perf.c
+++ b/tools/bpf/bpftool/perf.c
@@ -11,7 +11,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
-#include <ftw.h>
+#include <dirent.h>
 
 #include <bpf/bpf.h>
 
@@ -147,81 +147,83 @@ static void print_perf_plain(int pid, int fd, __u32 prog_id, __u32 fd_type,
        }
 }
 
-static int show_proc(const char *fpath, const struct stat *sb,
-                    int tflag, struct FTW *ftwbuf)
+static int show_proc(void)
 {
+       struct dirent *proc_de, *pid_fd_de;
        __u64 probe_offset, probe_addr;
        __u32 len, prog_id, fd_type;
-       int err, pid = 0, fd = 0;
+       DIR *proc, *pid_fd;
+       int err, pid, fd;
        const char *pch;
        char buf[4096];
 
-       /* prefix always /proc */
-       pch = fpath + 5;
-       if (*pch == '\0')
-               return 0;
+       proc = opendir("/proc");
+       if (!proc)
+               return -1;
 
-       /* pid should be all numbers */
-       pch++;
-       while (isdigit(*pch)) {
-               pid = pid * 10 + *pch - '0';
-               pch++;
-       }
-       if (*pch == '\0')
-               return 0;
-       if (*pch != '/')
-               return FTW_SKIP_SUBTREE;
-
-       /* check /proc/<pid>/fd directory */
-       pch++;
-       if (strncmp(pch, "fd", 2))
-               return FTW_SKIP_SUBTREE;
-       pch += 2;
-       if (*pch == '\0')
-               return 0;
-       if (*pch != '/')
-               return FTW_SKIP_SUBTREE;
-
-       /* check /proc/<pid>/fd/<fd_num> */
-       pch++;
-       while (isdigit(*pch)) {
-               fd = fd * 10 + *pch - '0';
-               pch++;
-       }
-       if (*pch != '\0')
-               return FTW_SKIP_SUBTREE;
+       while ((proc_de = readdir(proc))) {
+               pid = 0;
+               pch = proc_de->d_name;
 
-       /* query (pid, fd) for potential perf events */
-       len = sizeof(buf);
-       err = bpf_task_fd_query(pid, fd, 0, buf, &len, &prog_id, &fd_type,
-                               &probe_offset, &probe_addr);
-       if (err < 0)
-               return 0;
+               /* pid should be all numbers */
+               while (isdigit(*pch)) {
+                       pid = pid * 10 + *pch - '0';
+                       pch++;
+               }
+               if (*pch != '\0')
+                       continue;
 
-       if (json_output)
-               print_perf_json(pid, fd, prog_id, fd_type, buf, probe_offset,
-                               probe_addr);
-       else
-               print_perf_plain(pid, fd, prog_id, fd_type, buf, probe_offset,
-                                probe_addr);
+               err = snprintf(buf, sizeof(buf), "/proc/%s/fd", proc_de->d_name);
+               if (err < 0 || err >= (int)sizeof(buf))
+                       continue;
+
+               pid_fd = opendir(buf);
+               if (!pid_fd)
+                       continue;
 
+               while ((pid_fd_de = readdir(pid_fd))) {
+                       fd = 0;
+                       pch = pid_fd_de->d_name;
+
+                       /* fd should be all numbers */
+                       while (isdigit(*pch)) {
+                               fd = fd * 10 + *pch - '0';
+                               pch++;
+                       }
+                       if (*pch != '\0')
+                               continue;
+
+                       /* query (pid, fd) for potential perf events */
+                       len = sizeof(buf);
+                       err = bpf_task_fd_query(pid, fd, 0, buf, &len,
+                                               &prog_id, &fd_type,
+                                               &probe_offset, &probe_addr);
+                       if (err < 0)
+                               continue;
+
+                       if (json_output)
+                               print_perf_json(pid, fd, prog_id, fd_type, buf,
+                                               probe_offset, probe_addr);
+                       else
+                               print_perf_plain(pid, fd, prog_id, fd_type, buf,
+                                                probe_offset, probe_addr);
+               }
+               closedir(pid_fd);
+       }
+       closedir(proc);
        return 0;
 }
 
 static int do_show(int argc, char **argv)
 {
-       int flags = FTW_ACTIONRETVAL | FTW_PHYS;
-       int err = 0, nopenfd = 16;
+       int err;
 
        if (!has_perf_query_support())
                return -1;
 
        if (json_output)
                jsonw_start_array(json_wtr);
-       if (nftw("/proc", show_proc, nopenfd, flags) == -1) {
-               p_err("%s", strerror(errno));
-               err = -1;
-       }
+       err = show_proc();
        if (json_output)
                jsonw_end_array(json_wtr);