diff (diffutils 2.7) breaks with non-regular files on FreeBSD 4.1.1, with patch

[Timothy Miller]

GNU diff, from diffutils 2.7 breaks trying to diff files where at least one of
them is not a regular file. For instance, under zsh, prog1 <(prog2) takes the
output of prog2 and makes it available through a pipe whose name is then
substituted for <(prog1) as the argument to prog2, so I can do

diff -a <(g++ -E -dM -xc++ /dev/null) <(g++ -O -E -dM -xc++ /dev/null)

to see what the differences in preprocessor predefinitions are with optimization
turned on in g++. Unfortunately, that doesn't work with the current version of
diffutils on FreeBSD 4.1.1; instead it always reports the files as being the
same. I tracked this down to the fact that st_blksize is 0 for the nonregular
files zsh uses (/dev/fd/* in this case, but also /dev/null and various others),
and diff tries to double this value to get a buffer size to read the file in.
My patch to fix this is at the end of this email. current->bufsize is 
initialized on line 97 of io.c to st_blksize, fyi.
   Tim

--- io.c.dist   Wed Oct 29 11:14:35 1997
+++ io.c        Tue Aug  7 20:30:10 2001
@@ -165,7 +165,7 @@
        {
          if (current->buffered_chars == current->bufsize)
            {
-             current->bufsize = current->bufsize * 2;
+             current->bufsize = current->bufsize == 0 ? sizeof(word) : 
current->bufsize * 2;
              current->buffer = xrealloc (current->buffer, current->bufsize);
            }
          cc = read (current->desc,