bk commit into 5.0 tree (kaa:1.2535) BUG#31566

[Alexey Kopytov]

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ChangeSet@stripped, 2007-10-24 21:16:20+04:00, kaa@polly.(none) +1 -0
  Fix for bug #31566: my_write(fd, 0x0, 0, flags) fails with EFAULT on
  some platforms
  
  Since the behavior of write(fd, buf, 0) is undefined, it may fail with
  EFAULT on some architectures when buf == NULL. The error was propagated
  up to a caller, since my_write() code did not handle it properly.
  
  Fixed by checking the 'number of bytes' argument in my_write() and
  returning before calling the write() system call when there is nothing
  to write.

  mysys/my_write.c@stripped, 2007-10-24 21:16:12+04:00, kaa@polly.(none) +4 -0
    Return from my_write() before calling the write() system call when the
    number of bytes to be written is 0, since the behavior of write() in
    this case is not portable.

diff -Nrup a/mysys/my_write.c b/mysys/my_write.c
--- a/mysys/my_write.c	2007-03-28 20:01:08 +04:00
+++ b/mysys/my_write.c	2007-10-24 21:16:12 +04:00
@@ -29,6 +29,10 @@ uint my_write(int Filedes, const byte *B
 		   Filedes, (long) Buffer, Count, MyFlags));
   errors=0; written=0L;
 
+  /* The behavior of write(fd, buf, 0) is not portable */
+  if (unlikely(!Count))
+    return 0;
+  
   for (;;)
   {
     if ((writenbytes = (uint) write(Filedes, Buffer, Count)) == Count)