Automatically bump memlock ulimit

Instead of requiring the user to bump the ulimit in their shell before
starting a bcc script, try to setrlimit automatically when a failure
occurs. Since there is no getrusage for memlock limit, unfortunately we
have to brute force setting the limit. For now, just try bpf() once and
then try to set unlimited ulimit, then try bpf() again.

Fixes: #281
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/cc/libbpf.c

@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ioctl.h>
+#include <sys/resource.h>
 #include <unistd.h>
 
 #include "libbpf.h"
@@ -67,7 +68,19 @@ int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size, int
   attr.value_size = value_size;
   attr.max_entries = max_entries;
 
-  return syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
+  int ret = syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
+  if (ret < 0 && errno == EPERM) {
+    // see note below about the rationale for this retry
+
+    struct rlimit rl = {};
+    if (getrlimit(RLIMIT_MEMLOCK, &rl) == 0) {
+      rl.rlim_max = RLIM_INFINITY;
+      rl.rlim_cur = rl.rlim_max;
+      if (setrlimit(RLIMIT_MEMLOCK, &rl) == 0)
+        ret = syscall(__NR_bpf, BPF_MAP_CREATE, &attr, sizeof(attr));
+    }
+  }
+  return ret;
 }
 
 int bpf_update_elem(int fd, void *key, void *value, unsigned long long flags)
@@ -138,6 +151,24 @@ int bpf_prog_load(enum bpf_prog_type prog_type,
     log_buf[0] = 0;
 
   int ret = syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
+  if (ret < 0 && errno == EPERM) {
+    // When EPERM is returned, two reasons are possible:
+    //  1. user has no permissions for bpf()
+    //  2. user has insufficent rlimit for locked memory
+    // Unfortunately, there is no api to inspect the current usage of locked
+    // mem for the user, so an accurate calculation of how much memory to lock
+    // for this new program is difficult to calculate. As a hack, bump the limit
+    // to unlimited. If program load fails again, return the error.
+
+    struct rlimit rl = {};
+    if (getrlimit(RLIMIT_MEMLOCK, &rl) == 0) {
+      rl.rlim_max = RLIM_INFINITY;
+      rl.rlim_cur = rl.rlim_max;
+      if (setrlimit(RLIMIT_MEMLOCK, &rl) == 0)
+        ret = syscall(__NR_bpf, BPF_PROG_LOAD, &attr, sizeof(attr));
+    }
+  }
+
   if (ret < 0 && !log_buf) {
     // caller did not specify log_buf but failure should be printed,
     // so call recursively and print the result to stderr

tests/wrapper.sh.in

@@ -32,11 +32,11 @@ function ns_run() {
   sudo ip netns exec $ns ethtool -K eth0 tx off
   sudo ip addr add dev $ns.out 172.16.1.1/24
   sudo ip link set $ns.out up
-  sudo bash -c "ulimit -l 10240; PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH ip netns exec $ns $cmd $1 $2"
+  sudo bash -c "PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH ip netns exec $ns $cmd $1 $2"
   return $?
 }
 function sudo_run() {
-  sudo bash -c "ulimit -l 10240; PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd $1 $2"
+  sudo bash -c "PYTHONPATH=$PYTHONPATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH $cmd $1 $2"
   return $?
 }
 function simple_run() {