dd: work around buffer length restrictions with oflag=direct (O_DIRECT)

dd oflag=direct would fail to copy a file with size that is
not a multiple of 512 (destination file system specific)

* NEWS (Bug fixes): Mention it.
* src/dd.c (iwrite): Turn off O_DIRECT for any
smaller-than-obs-sized write.  Don't bother to restore it.
* tests/dd/direct: New test for the above.
* tests/Makefile.am (TESTS): Add dd/direct.
* doc/coreutils.texi (dd invocation): Mention oflag=direct
buffer size restriction.
Details in http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/17586
Reported by Eric Sandeen.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/dd.c b/src/dd.c
index 9a9d22ae7..43ad7189f 100644
--- a/src/dd.c
+++ b/src/dd.c
@@ -837,6 +837,14 @@ iwrite (int fd, char const *buf, size_t size)
 {
   size_t total_written = 0;
 
+  if ((output_flags & O_DIRECT) && size < output_blocksize)
+    {
+      int old_flags = fcntl (STDOUT_FILENO, F_GETFL);
+      if (fcntl (STDOUT_FILENO, F_SETFL, old_flags & ~O_DIRECT) != 0)
+        error (0, errno, _("failed to turn off O_DIRECT: %s"),
+               quote (output_file));
+    }
+
   while (total_written < size)
     {
       ssize_t nwritten;
@@ -1897,7 +1905,7 @@ main (int argc, char **argv)
 		  || S_ISDIR (stdout_stat.st_mode)
 		  || S_TYPEISSHM (&stdout_stat))
 		error (EXIT_FAILURE, ftruncate_errno,
-		       _("truncating at %"PRIuMAX" bytes in output file %s"),
+                   _("failed to truncate to %"PRIuMAX" bytes in output file %s"),
 		       size, quote (output_file));
 	    }
 	}