cat: avoid redundant pipe creation and resizing

* src/cat.c (splice_cat): Don't bother resizing input as it generally
doesn't help perf, and also save an fstat per input. Don't close the
intermediate pipe once created, unless there is an error reading from
it.

Co-authored-by: Pádraig Brady <P@draigBrady.com>

diff --git a/src/cat.c b/src/cat.c
index a9e2d717a1711c7d18618061ac4132c174b59451..43063fb9b27e1273da79f37a2fbea74c41435fc8 100644 (file)
--- a/src/cat.c
+++ b/src/cat.c
@@ -562,6 +562,25 @@ splice_cat (void)
 
 #if HAVE_SPLICE
 
+  /* If PIPEFD[0] is a non-negative value, we have an open pipe from a
+     previous call to this function.  At the start of this function the
+     pipe will always be empty.  */
+  static int pipefd[2] = { -1, -1 };
+
+  /* The size of the pipe referred to by PIPEFD.  */
+  static idx_t pipefd_pipe_size = 0;
+
+  /* Create an intermediate pipe if it is not already open.
+     Even if both input and output are pipes,
+     so that read and write errors can be distinguished.  */
+  if (pipefd[0] < 0)
+    {
+      if (pipe (pipefd) < 0)
+        return false;
+      pipefd_pipe_size = increase_pipe_size (pipefd[1]);
+    }
+
+  /* Increase the size of the pipe referred to by standard output.  */
   static int stdout_is_pipe = -1;
   static idx_t stdout_pipe_size = 0;
   if (stdout_is_pipe == -1)
@@ -571,20 +590,7 @@ splice_cat (void)
         stdout_pipe_size = increase_pipe_size (STDOUT_FILENO);
     }
 
-  bool input_is_pipe = 0 < isapipe (input_desc);
-
-  idx_t pipe_size = stdout_pipe_size;
-  if (input_is_pipe)
-    pipe_size = MAX (pipe_size, increase_pipe_size (input_desc));
-
-  int pipefd[2] = { -1, -1 };
-
-  /* Create an intermediate pipe.
-     Even if both input and output are pipes,
-     so that read and write errors can be distinguished.  */
-  if (pipe (pipefd) < 0)
-    return false;
-  pipe_size = MAX (pipe_size, increase_pipe_size (pipefd[1]));
+  idx_t pipe_size = MAX (pipefd_pipe_size, stdout_pipe_size);
 
   while (true)
     {
@@ -636,18 +642,20 @@ splice_cat (void)
 
  done:
   if (! in_ok && ! out_ok)
-    error (0, errno, "%s", _("splice error"));
-  else if (! in_ok)
-    error (0, errno, "%s", quotef (infile));
-  else if (! out_ok)
-    write_error ();
-  if (0 <= pipefd[0])
     {
+      /* Recreate the pipe on internal error.  */
       int saved_errno = errno;
       close (pipefd[0]);
       close (pipefd[1]);
       errno = saved_errno;
+      pipefd[0] = pipefd[1] = -1;
+      pipefd_pipe_size = 0;
+      error (0, errno, "%s", _("splice error"));
     }
+  else if (! in_ok)
+    error (0, errno, "%s", quotef (infile));
+  else if (! out_ok)
+    write_error ();
 #endif
 
   return (in_ok && out_ok) ? some_copied : -1;