Implement __zipos_dup (#972)

* Implement __zipos_dup

Makes ZiposHandle reference-counted by an `rc` field in a union with its
freelist `next` pointer. The functions `__zipos_free` and `__zipos_keep`
function as incref/decref for it. Adds `__zipos_postdup` to fix metadata
on file descriptors after dup-like operations, and adds zipos support to
`sys_dup_nt` + `sys_close_nt`.

* Remove noop __zipos_postdup

rc is never a zipos file because it is always a previously unused file
descriptor. fd is never a zipos file because that case has been handled
above by __zipos_fcntl.

libc/runtime/zipos-fcntl.c

@@ -16,13 +16,30 @@
 │ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/createfileflags.internal.h"
 #include "libc/calls/internal.h"
+#include "libc/calls/syscall-nt.internal.h"
+#include "libc/calls/syscall-sysv.internal.h"
 #include "libc/runtime/zipos.internal.h"
 #include "libc/sysv/consts/f.h"
 #include "libc/sysv/consts/fd.h"
 #include "libc/sysv/consts/o.h"
 #include "libc/sysv/errfuns.h"
 
+static int __zipos_dupfd(int fd, int cmd, int start) {
+  int rc;
+  if (start < 0) return einval();
+  if (IsWindows()) {
+    return sys_dup_nt(fd, -1, (cmd == F_DUPFD_CLOEXEC ? _O_CLOEXEC : 0),
+                      start);
+  }
+  rc = sys_fcntl(fd, cmd, start, __sys_fcntl);
+  if (rc != -1) {
+    __zipos_postdup(fd, rc);
+  }
+  return rc;
+}
+
 int __zipos_fcntl(int fd, int cmd, uintptr_t arg) {
   if (cmd == F_GETFD) {
     if (g_fds.p[fd].flags & O_CLOEXEC) {
@@ -38,6 +55,8 @@ int __zipos_fcntl(int fd, int cmd, uintptr_t arg) {
       g_fds.p[fd].flags &= ~O_CLOEXEC;
       return 0;
     }
+  } else if (cmd == F_DUPFD || cmd == F_DUPFD_CLOEXEC) {
+    return __zipos_dupfd(fd, cmd, arg);
   } else {
     return einval();
   }

libc/runtime/zipos-open.c

@@ -78,7 +78,20 @@ static void *__zipos_mmap_space(size_t mapsize) {
   return start + offset;
 }
 
+struct ZiposHandle *__zipos_keep(struct ZiposHandle *h) {
+  atomic_fetch_add_explicit(&h->refs, 1, memory_order_relaxed);
+  return h;
+}
+
+static bool __zipos_drop(struct ZiposHandle *h) {
+  int refs = atomic_load_explicit(&h->refs, memory_order_acquire);
+  return -1 == refs || -1 == atomic_fetch_sub(&h->refs, 1);
+}
+
 void __zipos_free(struct ZiposHandle *h) {
+  if (!__zipos_drop(h)) {
+    return;
+  }
   if (IsAsan()) {
     __asan_poison((char *)h + sizeof(struct ZiposHandle),
                   h->mapsize - sizeof(struct ZiposHandle), kAsanHeapFree);
@@ -100,7 +113,7 @@ StartOver:
   while ((h = *ph)) {
     if (h->mapsize >= mapsize) {
       if (!_cmpxchg(ph, h, h->next)) goto StartOver;
-      h->next = 0;
+      atomic_init(&h->refs, 0);
       break;
     }
     ph = &h->next;
@@ -209,6 +222,27 @@ static int __zipos_load(struct Zipos *zipos, size_t cf, int flags,
   return -1;
 }
 
+void __zipos_postdup(int oldfd, int newfd) {
+  if (oldfd == newfd) {
+    return;
+  }
+  if (__isfdkind(newfd, kFdZip)) {
+    __zipos_free((struct ZiposHandle *)(intptr_t)g_fds.p[newfd].handle);
+    if (!__isfdkind(oldfd, kFdZip)) {
+      __fds_lock();
+      bzero(g_fds.p + newfd, sizeof(*g_fds.p));
+      __fds_unlock();
+    }
+  }
+  if (__isfdkind(oldfd, kFdZip)) {
+    __zipos_keep((struct ZiposHandle *)(intptr_t)g_fds.p[oldfd].handle);
+    __fds_lock();
+    __ensurefds_unlocked(newfd);
+    g_fds.p[newfd] = g_fds.p[oldfd];
+    __fds_unlock();
+  }
+}
+
 /**
  * Loads compressed file from αcτµαlly pδrταblε εxεcµταblε object store.
  *

libc/runtime/zipos.S

@@ -33,6 +33,9 @@
 	.yoink	__zipos_stat
 	.yoink	__zipos_notat
 	.yoink	__zipos_mmap
+	.yoink  __zipos_postdup
+	.yoink  __zipos_keep
+	.yoink  __zipos_free
 
 //	TODO(jart): why does corruption happen when zip has no assets?
 	.yoink	.cosmo

libc/runtime/zipos.internal.h

@@ -20,8 +20,9 @@ struct ZiposHandle {
   struct Zipos *zipos;
   size_t size;
   size_t mapsize;
-  size_t pos;
   size_t cfile;
+  _Atomic(int) refs;
+  size_t pos;         // TODO atomic
   uint8_t *mem;
   uint8_t data[];
 };
@@ -38,6 +39,7 @@ struct Zipos {
 
 int __zipos_close(int);
 void __zipos_free(struct ZiposHandle *);
+struct ZiposHandle *__zipos_keep(struct ZiposHandle *);
 struct Zipos *__zipos_get(void) pureconst;
 size_t __zipos_normpath(char *, const char *, size_t);
 ssize_t __zipos_find(struct Zipos *, struct ZiposUri *);
@@ -45,6 +47,7 @@ ssize_t __zipos_scan(struct Zipos *, struct ZiposUri *);
 ssize_t __zipos_parseuri(const char *, struct ZiposUri *);
 uint64_t __zipos_inode(struct Zipos *, int64_t, const void *, size_t);
 int __zipos_open(struct ZiposUri *, int);
+void __zipos_postdup(int, int);
 int __zipos_access(struct ZiposUri *, int);
 int __zipos_stat(struct ZiposUri *, struct stat *);
 int __zipos_fstat(struct ZiposHandle *, struct stat *);