[LibOS] Add shared_cpu_list file to sysfs cache info

This is e.g. required by the gemm-common Rust crate, see
`gemm-common/src/cache.rs`. Without this file, the crate logic
incorrectly calculates shared-cpu count as zero and leads to a
division-by-zero exception.

Signed-off-by: Dmitrii Kuvaiskii <[email protected]>

libos/include/libos_fs_pseudo.h

@@ -74,6 +74,10 @@ struct libos_dev_ops {
  * Note: Used to allocate on stack; increase with caution or use malloc instead. */
 #define PAL_SYSFS_MAP_FILESZ 256
 
+/* Used to represent cpu ranges (lists) like "0-31,64-95,97".
+ * Note: Used to allocate on stack; increase with caution or use malloc instead. */
+#define PAL_SYSFS_RANGES_FILESZ 512
+
 /*
  * A node of the pseudo filesystem. A single node can describe either a single file, or a family of
  * files:

libos/src/fs/sys/cache_info.c

@@ -44,14 +44,26 @@ int sys_cache_load(struct libos_dentry* dent, char** out_data, size_t* out_size)
     const struct pal_topo_info* topo = &g_pal_public_state->topo_info;
     size_t cache_idx = topo->threads[thread_id].ids_of_caches[cache_class];
     const struct pal_cache_info* cache = &topo->caches[cache_idx];
-    char str[PAL_SYSFS_MAP_FILESZ] = {'\0'};
+
+    /* str buffer of the same size is used for all below pseudo-files; we pick the largest size for
+     * this buffer (which is presumably the size required for the "shared_cpu_list" file) */
+    static_assert(PAL_SYSFS_RANGES_FILESZ >= PAL_SYSFS_MAP_FILESZ, "sysfs file size too small");
+    char str[PAL_SYSFS_RANGES_FILESZ] = {'\0'};
+
     if (strcmp(name, "shared_cpu_map") == 0) {
         struct callback_arg callback_arg = {
             .cache_id_to_match = cache_idx,
             .cache_class = cache_class,
         };
         ret = sys_print_as_bitmask(str, sizeof(str), topo->threads_cnt,
                                    is_same_cache, &callback_arg);
+    } else if (strcmp(name, "shared_cpu_list") == 0) {
+        struct callback_arg callback_arg = {
+            .cache_id_to_match = cache_idx,
+            .cache_class = cache_class,
+        };
+        ret = sys_print_as_ranges(str, sizeof(str), topo->threads_cnt,
+                                  is_same_cache, &callback_arg);
     } else if (strcmp(name, "level") == 0) {
         ret = snprintf(str, sizeof(str), "%zu\n", cache->level);
     } else if (strcmp(name, "type") == 0) {

libos/src/fs/sys/cpu_info.c

@@ -31,7 +31,7 @@ int sys_cpu_general_load(struct libos_dentry* dent, char** out_data, size_t* out
     int ret;
     const struct pal_topo_info* topo = &g_pal_public_state->topo_info;
     const char* name = dent->name;
-    char str[PAL_SYSFS_BUF_FILESZ];
+    char str[PAL_SYSFS_RANGES_FILESZ];
 
     if (strcmp(name, "online") == 0) {
         ret = sys_print_as_ranges(str, sizeof(str), topo->threads_cnt, is_online, NULL);

libos/src/fs/sys/fs.c

@@ -269,6 +269,7 @@ static void init_cpu_dir(struct pseudo_node* cpu) {
     indexX->list_names = &sys_resource_list_names;
 
     pseudo_add_str(indexX, "shared_cpu_map", &sys_cache_load);
+    pseudo_add_str(indexX, "shared_cpu_list", &sys_cache_load);
     pseudo_add_str(indexX, "level", &sys_cache_load);
     pseudo_add_str(indexX, "type", &sys_cache_load);
     pseudo_add_str(indexX, "size", &sys_cache_load);

libos/src/fs/sys/node_info.c

@@ -30,7 +30,7 @@ int sys_node_general_load(struct libos_dentry* dent, char** out_data, size_t* ou
     int ret;
     const struct pal_topo_info* topo = &g_pal_public_state->topo_info;
     const char* name = dent->name;
-    char str[PAL_SYSFS_BUF_FILESZ];
+    char str[PAL_SYSFS_RANGES_FILESZ];
     if (strcmp(name, "online") == 0) {
         ret = sys_print_as_ranges(str, sizeof(str), topo->numa_nodes_cnt, is_online, NULL);
     } else if (strcmp(name, "possible") == 0) {