[LibOS] Add /sys/devices/system/cpu/kernel_max file

Signed-off-by: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@intel.com>
gramineproject · Aug 21, 2023 · 028d580 · 028d580
1 parent 9ef75eb
commit 028d580
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Showing 2 changed files with 29 additions and 0 deletions.
diff --git a/libos/src/fs/sys/fs.c b/libos/src/fs/sys/fs.c
@@ -13,6 +13,23 @@
 #include "libos_fs.h"
 #include "libos_fs_pseudo.h"
 
+#define DEFAULT_KERNEL_MAX_CPUS 8192
+static uint32_t g_kernel_max_cpus = DEFAULT_KERNEL_MAX_CPUS;
+
+static int sys_cpu_kernel_max(struct libos_dentry* dent, char** out_data, size_t* out_size) {
+ __UNUSED(dent);
+ char str[32];
+
+ /* `- 1` because Linux always reports kernel_max like this */
+ int ret = snprintf(str, sizeof(str), "%u\n", g_kernel_max_cpus - 1);
+ if (ret < 0)
+ return ret;
+ if ((size_t)ret >= sizeof(str))
+ return -ERANGE;
+
+ return sys_load(str, out_data, out_size);
+}
+
 int sys_print_as_ranges(char* buf, size_t buf_size, size_t count,
  bool (*is_present)(size_t ind, const void* arg), const void* callback_arg) {
  size_t buf_pos = 0;
@@ -206,6 +223,17 @@ int sys_load(const char* str, char** out_data, size_t* out_size) {
 }
 
 static void init_cpu_dir(struct pseudo_node* cpu) {
+ uint32_t next_power_of_2 = DEFAULT_KERNEL_MAX_CPUS;
+ assert(IS_POWER_OF_2(next_power_of_2));
+
+ while (next_power_of_2 < g_pal_public_state->topo_info.threads_cnt) {
+ /* this should never happen in real systems, so BUG() railguard is enough */
+ if (__builtin_mul_overflow(next_power_of_2, 2, &next_power_of_2))
+ BUG();
+ }
+ g_kernel_max_cpus = next_power_of_2;
+
+ pseudo_add_str(cpu, "kernel_max", &sys_cpu_kernel_max);
  pseudo_add_str(cpu, "online", &sys_cpu_general_load);
  pseudo_add_str(cpu, "offline", &sys_cpu_general_load);
  pseudo_add_str(cpu, "possible", &sys_cpu_general_load);

diff --git a/libos/test/regression/test_libos.py b/libos/test/regression/test_libos.py
@@ -1146,6 +1146,7 @@ def test_040_sysfs(self):
  self.assertIn('/sys/devices/system/cpu/offline: file', lines)
  self.assertIn('/sys/devices/system/cpu/possible: file', lines)
  self.assertIn('/sys/devices/system/cpu/present: file', lines)
+ self.assertIn('/sys/devices/system/cpu/kernel_max: file', lines)
  for i in range(cpus_cnt):
  cpu = f'/sys/devices/system/cpu/cpu{i}'
  self.assertIn(f'{cpu}: directory', lines)