Rename __zipos_free -> __zipos_drop (#1043)

Removes the separate decref function, uses keep/drop in the internal
API.

Author: mrdomino

libc/runtime/zipos-close.c

@@ -39,7 +39,7 @@ int __zipos_close(int fd) {
   if (!__vforked) {
     struct ZiposHandle *h;
     h = (struct ZiposHandle *)(intptr_t)g_fds.p[fd].handle;
-    __zipos_free(h);
+    __zipos_drop(h);
   }
   return rc;
 }

libc/runtime/zipos-open.c

@@ -88,18 +88,11 @@ struct ZiposHandle *__zipos_keep(struct ZiposHandle *h) {
   return h;
 }
 
-static bool __zipos_drop(struct ZiposHandle *h) {
-  if (!atomic_fetch_sub_explicit(&h->refs, 1, memory_order_release)) {
-    atomic_thread_fence(memory_order_acquire);
-    return true;
-  }
-  return false;
-}
-
-void __zipos_free(struct ZiposHandle *h) {
-  if (!__zipos_drop(h)) {
+void __zipos_drop(struct ZiposHandle *h) {
+  if (atomic_fetch_sub_explicit(&h->refs, 1, memory_order_release)) {
     return;
   }
+  atomic_thread_fence(memory_order_acquire);
   if (IsAsan()) {
     __asan_poison((char *)h + sizeof(struct ZiposHandle),
                   h->mapsize - sizeof(struct ZiposHandle), kAsanHeapFree);
@@ -227,7 +220,7 @@ static int __zipos_load(struct Zipos *zipos, size_t cf, int flags,
     }
     __fds_unlock();
   }
-  __zipos_free(h);
+  __zipos_drop(h);
   return -1;
 }
 
@@ -238,7 +231,7 @@ void __zipos_postdup(int oldfd, int newfd) {
   BLOCK_SIGNALS;
   __fds_lock();
   if (__isfdkind(newfd, kFdZip)) {
-    __zipos_free((struct ZiposHandle *)(intptr_t)g_fds.p[newfd].handle);
+    __zipos_drop((struct ZiposHandle *)(intptr_t)g_fds.p[newfd].handle);
     if (!__isfdkind(oldfd, kFdZip)) {
       bzero(g_fds.p + newfd, sizeof(*g_fds.p));
     }

libc/runtime/zipos.S

@@ -35,7 +35,7 @@
 	.yoink	__zipos_mmap
 	.yoink  __zipos_postdup
 	.yoink  __zipos_keep
-	.yoink  __zipos_free
+	.yoink  __zipos_drop
 
 //	TODO(jart): why does corruption happen when zip has no assets?
 	.yoink	.cosmo

libc/runtime/zipos.internal.h

@@ -38,7 +38,7 @@ struct Zipos {
 };
 
 int __zipos_close(int);
-void __zipos_free(struct ZiposHandle *);
+void __zipos_drop(struct ZiposHandle *);
 struct ZiposHandle *__zipos_keep(struct ZiposHandle *);
 struct Zipos *__zipos_get(void) pureconst;
 size_t __zipos_normpath(char *, const char *, size_t);