Kernel: Make file descriptor numbers reusable.

Instead of using the "append only" list it now uses "relist" which
allows for indexes to be removed.

1 files changed, 120 insertions, 0 deletions

diff --git a/kernel/lib/relist.c b/kernel/lib/relist.c
new file mode 100644
index 0000000..6ad30d2
--- /dev/null
+++ b/kernel/lib/relist.c
@@ -0,0 +1,120 @@
+#include <assert.h>
+#include <kmalloc.h>
+#include <lib/relist.h>
+
+void relist_init(struct relist *list) {
+  list->bitmap_capacity = 100;
+  list->bitmap = kcalloc(sizeof(u64), list->bitmap_capacity);
+  if (!list->bitmap) {
+    goto relist_init_error;
+  }
+  list->entries = kallocarray(sizeof(void *), (sizeof(u64) * 8));
+  if (!list->entries) {
+    goto relist_init_error;
+  }
+  return;
+
+// Can't allocate now but future appends can try to allocate anyways so
+// there is no reason to "fail" the init.
+relist_init_error:
+  list->bitmap_capacity = 0;
+  list->entries = NULL;
+  list->bitmap = NULL;
+  return;
+}
+
+void relist_reset(struct relist *list) {
+  memset(list->bitmap, 0, list->bitmap_capacity * sizeof(u64));
+}
+
+int relist_clone(struct relist *in, struct relist *out) {
+  relist_init(out);
+  for (int i = 0;; i++) {
+    void *output;
+    if (!relist_get(in, i, &output)) {
+      break;
+    }
+    if (!relist_add(out, output, NULL)) {
+      relist_free(out);
+      return 0;
+    }
+  }
+  return 1;
+}
+
+static int relist_find_free_entry(struct relist *list, u32 *entry) {
+  for (u32 i = 0; i < list->bitmap_capacity; i++) {
+    if (0 == ~(list->bitmap[i])) {
+      continue;
+    }
+
+    for (int c = 0; c < 64; c++) {
+      if (!(list->bitmap[i] & ((u64)1 << c))) {
+        *entry = i * 64 + c;
+        return 1;
+      }
+    }
+  }
+  *entry = 0;
+  return 0;
+}
+
+int relist_add(struct relist *list, void *value, u32 *index) {
+  u32 entry;
+  if (!relist_find_free_entry(list, &entry)) {
+    assert(0);
+  }
+  list->entries[entry] = value;
+  if (index) {
+    *index = entry;
+  }
+  list->bitmap[entry / 64] |= ((u64)1 << (entry % 64));
+  return 1;
+}
+
+int relist_remove(struct relist *list, u32 index) {
+  if ((index / 64) > list->bitmap_capacity) {
+    assert(0);
+    return 0;
+  }
+  int is_used = (list->bitmap[index / 64] & ((u64)1 << (index % 64)));
+  if (!is_used) {
+    assert(0);
+    return 0;
+  }
+  list->bitmap[index / 64] &= ~((u64)1 << (index % 64));
+  return 1;
+}
+
+int relist_set(struct relist *list, u32 index, void *value) {
+  assert(value);
+  if ((index / 64) > list->bitmap_capacity) {
+    assert(0);
+    return 0;
+  }
+  int is_used = (list->bitmap[index / 64] & ((u64)1 << (index % 64)));
+  assert(is_used);
+  list->entries[index] = value;
+  return 1;
+}
+
+int relist_get(const struct relist *list, u32 index, void **out) {
+  if ((index / 64) > list->bitmap_capacity) {
+    assert(0);
+    return 0;
+  }
+  int is_used = (list->bitmap[index / 64] & ((u64)1 << (index % 64)));
+  if (!is_used) {
+    return 0;
+  }
+  *out = list->entries[index];
+  return 1;
+}
+
+void relist_free(struct relist *list) {
+  list->bitmap_capacity = 0;
+  kfree(list->entries);
+  kfree(list->bitmap);
+  list->entries = NULL;
+  list->bitmap = NULL;
+}