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Proposed new feature for bash: unbuffered pipes, part 4: glibc.diff

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diff --git a/libio/filedoalloc.c b/libio/filedoalloc.c
index 412b8d5937..35044e3512 100644
--- a/libio/filedoalloc.c
+++ b/libio/filedoalloc.c
@@ -58,6 +58,7 @@
 #include "libioP.h"
 #include <device-nrs.h>
 #include <sys/stat.h>
+#include <sys/types.h>
 #include <stdlib.h>
 #include <unistd.h>
 
@@ -71,6 +72,17 @@ local_isatty (int fd)
   return res;
 }
 
+struct _IO_stdout_unbuffered
+{
+  int initialized;
+  int present;
+  dev_t dev;
+  ino_t ino;
+} _IO_stdout_unbuffered_values;
+
+static void
+process_stdout_unbuffered (void);
+
 /* Allocate a file buffer, or switch to unbuffered I/O.  Streams for
    TTY devices default to line buffered.  */
 int
@@ -80,9 +92,23 @@ _IO_file_doallocate (FILE *fp)
   char *p;
   struct stat64 st;
 
+  /* Check to see if buffering of stdout has been suppressed. */
+  if (! _IO_stdout_unbuffered_values.initialized)
+    {
+      process_stdout_unbuffered();
+    }
+
   size = BUFSIZ;
   if (fp->_fileno >= 0 && __builtin_expect (_IO_SYSSTAT (fp, &st), 0) >= 0)
     {
+      // If this fd matched STDOUT_UNBUFFERED ...
+      if (_IO_stdout_unbuffered_values.present &&
+	  _IO_stdout_unbuffered_values.dev == st.st_dev &&
+	  _IO_stdout_unbuffered_values.ino == st.st_ino)
+	{
+	  fp->_flags |= _IO_UNBUFFERED;
+	  return 1;
+	}  
       if (S_ISCHR (st.st_mode))
 	{
 	  /* Possibly a tty.  */
@@ -105,3 +131,26 @@ _IO_file_doallocate (FILE *fp)
   return 1;
 }
 libc_hidden_def (_IO_file_doallocate)
+
+/* Examine the STDOUT_UNBUFFERED environment variable, if any.
+   If it has the format NNNN:NNNN, parse those numbers into
+   _IP_stdout_unbuffered_values. */
+static void
+process_stdout_unbuffered (void)
+{
+  _IO_stdout_unbuffered_values.initialized = 1;
+  _IO_stdout_unbuffered_values.present = 0;
+  char *su_value = getenv("STDOUT_UNBUFFERED");
+  if (!su_value)
+    return;
+  char *p1;
+  _IO_stdout_unbuffered_values.dev = strtoul(su_value, &p1, 10);
+  if (*p1 != ':')
+    return;
+  char *p2;
+  _IO_stdout_unbuffered_values.ino = strtoul(p1+1, &p2, 10);
+  if (*p2)
+    return;
+  // Enable the values that we have set.
+  _IO_stdout_unbuffered_values.present = 1;
+}

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Proposed new feature for bash:  unbuffered pipes, part 4: glibc.diff worley@alum.mit.edu (Dale R. Worley) - 2020-04-21 20:40 -0400

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