linux: read free/total memory from /proc/meminfo

It was reported that uv_get_free_memory() and uv_get_total_memory()
report the wrong values inside an lxc container.

Libuv calls sysinfo(2) but that isn't intercepted by lxc. /proc/meminfo
however is because /proc is a FUSE fs inside the container.

This commit makes libuv try /proc/meminfo first and fall back to
sysinfo(2) in case /proc isn't mounted.

Fixes: https://github.com/libuv/libuv/issues/2249
PR-URL: https://github.com/libuv/libuv/pull/2258
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

CMakeLists.txt

@@ -297,8 +297,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
        src/unix/linux-inotify.c
        src/unix/linux-syscalls.c
        src/unix/procfs-exepath.c
-       src/unix/sysinfo-loadavg.c
-       src/unix/sysinfo-memory.c)
+       src/unix/sysinfo-loadavg.c)
 endif()
 
 if(CMAKE_SYSTEM_NAME STREQUAL "NetBSD")

Makefile.am

@@ -425,8 +425,7 @@ libuv_la_SOURCES += src/unix/linux-core.c \
                     src/unix/linux-syscalls.h \
                     src/unix/procfs-exepath.c \
                     src/unix/proctitle.c \
-                    src/unix/sysinfo-loadavg.c \
-                    src/unix/sysinfo-memory.c
+                    src/unix/sysinfo-loadavg.c
 test_run_tests_LDFLAGS += -lutil
 endif
 

src/unix/linux-core.c

@@ -936,3 +936,75 @@ void uv__set_process_title(const char* title) {
   prctl(PR_SET_NAME, title);  /* Only copies first 16 characters. */
 #endif
 }
+
+
+static uint64_t uv__read_proc_meminfo(const char* what) {
+  unsigned long rc;
+  ssize_t n;
+  char* p;
+  int fd;
+  char buf[4096];  /* Large enough to hold all of /proc/meminfo. */
+
+  rc = 0;
+  fd = uv__open_cloexec("/proc/meminfo", O_RDONLY);
+
+  if (fd == -1)
+    return 0;
+
+  n = read(fd, buf, sizeof(buf) - 1);
+
+  if (n <= 0)
+    goto out;
+
+  buf[n] = '\0';
+  p = strstr(buf, what);
+
+  if (p == NULL)
+    goto out;
+
+  p += strlen(what);
+
+  if (1 != sscanf(p, "%lu kB", &rc))
+    goto out;
+
+  rc *= 1024;
+
+out:
+
+  if (uv__close_nocheckstdio(fd))
+    abort();
+
+  return rc;
+}
+
+
+uint64_t uv_get_free_memory(void) {
+  struct sysinfo info;
+  uint64_t rc;
+
+  rc = uv__read_proc_meminfo("MemFree:");
+
+  if (rc != 0)
+    return rc;
+
+  if (0 == sysinfo(&info))
+    return (uint64_t) info.freeram * info.mem_unit;
+
+  return 0;
+}
+
+
+uint64_t uv_get_total_memory(void) {
+  struct sysinfo info;
+  uint64_t rc;
+
+  rc = uv__read_proc_meminfo("MemTotal:");
+
+  if (rc != 0)
+    return rc;
+
+  if (0 == sysinfo(&info))
+    return (uint64_t) info.totalram * info.mem_unit;
+
+  return 0;
+}

uv.gyp

@@ -241,7 +241,6 @@
             'src/unix/linux-syscalls.h',
             'src/unix/procfs-exepath.c',
             'src/unix/sysinfo-loadavg.c',
-            'src/unix/sysinfo-memory.c',
           ],
           'link_settings': {
             'libraries': [ '-ldl', '-lrt' ],