Remember if lseek works in this FD.

It will be used in clang in a sec.

llvm-svn: 234619

2 files changed, 6 insertions, 1 deletions

diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h
index 6b0bde73db6..c378fa95763 100644
--- a/llvm/include/llvm/Support/raw_ostream.h
+++ b/llvm/include/llvm/Support/raw_ostream.h
@@ -333,6 +333,8 @@ class raw_fd_ostream : public raw_ostream {
 
   uint64_t pos;
 
+  bool SupportsSeeking;
+
   /// See raw_ostream::write_impl.
   void write_impl(const char *Ptr, size_t Size) override;
 
@@ -370,6 +372,8 @@ public:
   /// fsync.
   void close();
 
+  bool supportsSeeking() { return SupportsSeeking; }
+
   /// Flushes the stream and repositions the underlying file descriptor position
   /// to the offset specified from the beginning of the file.
   uint64_t seek(uint64_t off);
diff --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp
index b7e9ba616d5..199f0a6185b 100644
--- a/llvm/lib/Support/raw_ostream.cpp
+++ b/llvm/lib/Support/raw_ostream.cpp
@@ -525,7 +525,8 @@ raw_fd_ostream::raw_fd_ostream(int fd, bool shouldClose, bool unbuffered)
 
   // Get the starting position.
   off_t loc = ::lseek(FD, 0, SEEK_CUR);
-  if (loc == (off_t)-1)
+  SupportsSeeking = loc != (off_t)-1;
+  if (!SupportsSeeking)
     pos = 0;
   else
     pos = static_cast<uint64_t>(loc);