Merge "Simplify close(2) EINTR handling."

1 files changed, 56 insertions, 0 deletions

diff --git a/libc/bionic/close.cpp b/libc/bionic/close.cpp
new file mode 100644
index 0000000..18225f0
--- /dev/null
+++ b/libc/bionic/close.cpp
@@ -0,0 +1,56 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <unistd.h>
+
+extern "C" int ___close(int);
+
+int close(int fd) {
+  int rc = ___close(fd);
+  if (rc == -1 && errno == EINTR) {
+    // POSIX says that if close returns with EINTR, the fd must not be closed.
+    // Linus disagrees: http://lkml.indiana.edu/hypermail/linux/kernel/0509.1/0877.html
+    // The future POSIX solution is posix_close (http://austingroupbugs.net/view.php?id=529),
+    // with the state after EINTR being undefined, and EINPROGRESS for the case where close
+    // was interrupted by a signal but the file descriptor was actually closed.
+    // My concern with that future behavior is that it breaks existing code that assumes
+    // that close only returns -1 if it failed. Unlike other system calls, I have real
+    // difficulty even imagining a caller that would need to know that close was interrupted
+    // but succeeded. So returning EINTR is wrong (because Linux always closes) and EINPROGRESS
+    // is harmful because callers need to be rewritten to understand that EINPROGRESS isn't
+    // actually a failure, but will be reported as one.
+
+    // We don't restore errno because that would incur a cost (the TLS read) for every caller.
+    // Since callers don't know ahead of time whether close will legitimately fail, they need
+    // to have stashed the old errno value anyway if they plan on using it afterwards, so
+    // us clobbering errno here doesn't change anything in that respect.
+    return 0;
+  }
+  return rc;
+}