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Re: [PATCH] PR libstdc++/83279 handle sendfile not copying entire file


On 14/12/17 21:53 +0000, Jonathan Wakely wrote:
I failed to notice that the man page for sendfile(3) says it won't
copy more than 2GiB. This refactors the code to first try sendfile
(because it's fast if it works) and if that fails, or stops before the
end of the file, then use filebufs to copy what's left over.

I'm not adding a test because creating two files larger than 2G isn't
a good idea, but I've tested it locally.

	PR libstdc++/83279
	* src/filesystem/std-ops.cc (do_copy_file): Handle sendfile not
	copying entire file.


This restores the non-null offset argument to sendfile, which is
required by Solaris.

Tested x86_64-linux, committed to trunk.


commit d448551ca3cbbfd35796609128d54c8a0030a032
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Jan 5 21:04:54 2018 +0000

    PR libstdc++/83279 Use non-null offset argument for sendfile
    
            PR libstdc++/83279
            * src/filesystem/std-ops.cc  (do_copy_file): Use non-null offset with
            sendfile.

diff --git a/libstdc++-v3/src/filesystem/std-ops.cc b/libstdc++-v3/src/filesystem/std-ops.cc
index 2411bbb7977..bed1ad1fe27 100644
--- a/libstdc++-v3/src/filesystem/std-ops.cc
+++ b/libstdc++-v3/src/filesystem/std-ops.cc
@@ -382,10 +382,10 @@ fs::do_copy_file(const char* from, const char* to,
       return false;
     }
 
-  ssize_t n = 0;
   size_t count = from_st->st_size;
 #ifdef _GLIBCXX_USE_SENDFILE
-  n = ::sendfile(out.fd, in.fd, nullptr, count);
+  off_t offset = 0;
+  ssize_t n = ::sendfile(out.fd, in.fd, &offset, count);
   if (n < 0 && errno != ENOSYS && errno != EINVAL)
     {
       ec.assign(errno, std::generic_category());
@@ -405,35 +405,32 @@ fs::do_copy_file(const char* from, const char* to,
     count -= n;
 #endif // _GLIBCXX_USE_SENDFILE
 
-  __gnu_cxx::stdio_filebuf<char> sbin(in.fd, std::ios::in);
-  __gnu_cxx::stdio_filebuf<char> sbout(out.fd, std::ios::out);
+  using std::ios;
+  __gnu_cxx::stdio_filebuf<char> sbin(in.fd, ios::in|ios::binary);
+  __gnu_cxx::stdio_filebuf<char> sbout(out.fd, ios::out|ios::binary);
 
   if (sbin.is_open())
     in.fd = -1;
   if (sbout.is_open())
     out.fd = -1;
 
-  const std::streampos errpos(std::streamoff(-1));
-
-  if (n < 0)
+#ifdef _GLIBCXX_USE_SENDFILE
+  if (n != 0)
     {
-      auto p1 = sbin.pubseekoff(0, std::ios_base::beg, std::ios_base::in);
-      auto p2 = sbout.pubseekoff(0, std::ios_base::beg, std::ios_base::out);
+      if (n < 0)
+	n = 0;
+
+      const auto p1 = sbin.pubseekoff(n, ios::beg, ios::in);
+      const auto p2 = sbout.pubseekoff(n, ios::beg, ios::out);
+
+      const std::streampos errpos(std::streamoff(-1));
       if (p1 == errpos || p2 == errpos)
 	{
 	  ec = std::make_error_code(std::errc::io_error);
 	  return false;
 	}
     }
-  else if (n > 0)
-    {
-      auto p = sbout.pubseekoff(n, std::ios_base::beg, std::ios_base::out);
-      if (p == errpos)
-	{
-	  ec = std::make_error_code(std::errc::io_error);
-	  return false;
-	}
-    }
+#endif
 
   if (count && !(std::ostream(&sbout) << &sbin))
     {

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