Extend PipePosix with child_processes_inherit support - to control whether pipe handles should be inherited by a child process.

[ovyalov]

Summary

In order to control resource sharing between processes Pipe::Open() has given a new argument bool child_processes_inherit .
If child_processes_inherit is false take following approaches:

1. On Linux, FreeBSD 10 or higher - use pipe2 with O_CLOEXEC flag.
2. Otherwise - set FD_CLOEXEC flag on read and write pipe descriptors after successful pipe creation.

[emaste]

source/Host/posix/PipePosix.cpp

183–184

Not sure this is necessary

[clayborg]

Looks good

[ovyalov]

Removed #undef PIPE2_SUPPORTED - since it's a source file no need to undef the macro explicitly.

Thank you!

[emaste]

LGTM

[emaste]

rL222541

include/lldb/Host/posix/PipePosix.h

 public:
     static int kInvalidDescriptor;
     
     Pipe();
     
     ~Pipe();
     
     bool
-    Open();
+    Open(bool child_processes_inherit = false);
 
     bool
     IsValid() const;
     
     bool
     ReadDescriptorIsValid() const;
 
     bool

source/Host/posix/ConnectionFileDescriptorPosix.cpp

 
 void
 ConnectionFileDescriptor::OpenCommandPipe()
 {
     CloseCommandPipe();
 
     Log *log(lldb_private::GetLogIfAnyCategoriesSet(LIBLLDB_LOG_CONNECTION));
     // Make the command file descriptor here:
-    if (!m_pipe.Open())
+    if (!m_pipe.Open(m_child_processes_inherit))
     {
         if (log)
             log->Printf("%p ConnectionFileDescriptor::OpenCommandPipe () - could not make pipe: %s", static_cast<void *>(this),
                         strerror(errno));
     }
     else
     {
         if (log)

source/Host/posix/PipePosix.cpp

 //===-- PipePosix.cpp -------------------------------------------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Host/posix/PipePosix.h"
 
 #include <unistd.h>
+#include <fcntl.h>
 
 using namespace lldb_private;
 
 int Pipe::kInvalidDescriptor = -1;
 
 enum PIPES { READ, WRITE }; // Constants 0 and 1 for READ and WRITE
 
+// pipe2 is supported by Linux, FreeBSD v10 and higher.
+// TODO: Add more platforms that support pipe2.
+#define PIPE2_SUPPORTED defined(__linux__) || (defined(__FreeBSD__) && __FreeBSD__ >= 10)
+
+namespace
+{
+
+#if defined(FD_CLOEXEC) && !PIPE2_SUPPORTED
+bool SetCloexecFlag(int fd)
+{
+    int flags = ::fcntl(fd, F_GETFD);
+    if (flags == -1)
+        return false;
+    return (::fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == 0);
+}
+#endif
+
+}
+
 Pipe::Pipe()
 {
     m_fds[READ] = Pipe::kInvalidDescriptor;
     m_fds[WRITE] = Pipe::kInvalidDescriptor;
 }
 
 Pipe::~Pipe()
 {
     Close();
 }
 
 bool
-Pipe::Open()
+Pipe::Open(bool child_processes_inherit)
 {
     if (IsValid())
         return true;
 
+#if PIPE2_SUPPORTED
+    if (::pipe2(m_fds, (child_processes_inherit) ? 0 : O_CLOEXEC) == 0)
+        return true;
+#else
     if (::pipe(m_fds) == 0)
+    {
+#ifdef FD_CLOEXEC
+        if (!child_processes_inherit)
+        {
+            if (!SetCloexecFlag(m_fds[0]) || !SetCloexecFlag(m_fds[1]))
+            {
+                Close();
+                return false;
+            }
+        }
+#endif
         return true;
+    }
+#endif
 
     m_fds[READ] = Pipe::kInvalidDescriptor;
     m_fds[WRITE] = Pipe::kInvalidDescriptor;
     return false;
 }
 
 int
 Pipe::GetReadFileDescriptor() const

 Pipe::Write (const void *buf, size_t num_bytes)
 {
     if (WriteDescriptorIsValid())
     {
         const int fd = GetWriteFileDescriptor();
         return write (fd, buf, num_bytes);
     }
     return 0; // Return 0 since errno won't be set if we didn't call write
 }