os: avoid second fcntl syscall in NewFile on unix

CL 494915 introduced an additional fcntl(F_GETFL) syscall to determine
whether the file is in append-only mode. The existing unix.IsNonblock
call also issues an fcntl(F_GETFL) syscall. The two can be combined and
both the append-only mode and the non-blocking flags can be determined
from that syscall's result.

Change-Id: I915589ed94e079f6abaa2fd0032ef01f78698f7f
Reviewed-on: https://go-review.googlesource.com/c/go/+/497075
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>

diff --git a/src/os/file_unix.go b/src/os/file_unix.go
index 25ce83bf9dc3248261a405959ce81287961c9fb4..a34de8333da49b57aeccf07b358cad9e0be670ee 100644 (file)
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -104,13 +104,15 @@ func (f *File) Fd() uintptr {
 // constraints apply.
 func NewFile(fd uintptr, name string) *File {
        kind := kindNewFile
-       if nb, err := unix.IsNonblock(int(fd)); err == nil && nb {
-               kind = kindNonBlock
-       }
-       f := newFile(fd, name, kind)
+       appendMode := false
        if flags, err := unix.Fcntl(int(fd), syscall.F_GETFL, 0); err == nil {
-               f.appendMode = flags&syscall.O_APPEND != 0
+               if unix.HasNonblockFlag(flags) {
+                       kind = kindNonBlock
+               }
+               appendMode = flags&syscall.O_APPEND != 0
        }
+       f := newFile(fd, name, kind)
+       f.appendMode = appendMode
        return f
 }