stdio buffering extension

[christos%zoulas.com@localhost (Christos Zoulas)]

Hi,

After discussing importing stdbuf(1) from FreeBSD with various
people, they objected about it using LD_PRELOAD and suggested to
use the environment directly to alter the default buffering policy.

Here's an implementation of that...

Suggestions/Comments?

christos

Index: fopen.3
===================================================================
RCS file: /cvsroot/src/lib/libc/stdio/fopen.3,v
retrieving revision 1.30
diff -u -u -r1.30 fopen.3
--- fopen.3	11 Feb 2015 15:19:05 -0000	1.30
+++ fopen.3	14 Jul 2015 20:16:45 -0000
@@ -196,6 +196,13 @@
 .Em stdin ,
 or
 .Em stdout ) .
+.Pp
+Input and output against the opened stream will be fully buffered, unless
+it refers to an interactive terminal device, or a different kind of buffering
+is specified in the environment.
+See
+.Xr setvbuf 3
+for additional details.
 .Sh RETURN VALUES
 Upon successful completion
 .Fn fopen ,
Index: makebuf.c
===================================================================
RCS file: /cvsroot/src/lib/libc/stdio/makebuf.c,v
retrieving revision 1.17
diff -u -u -r1.17 makebuf.c
--- makebuf.c	15 Mar 2012 18:22:30 -0000	1.17
+++ makebuf.c	14 Jul 2015 20:16:45 -0000
@@ -49,10 +49,64 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <inttypes.h>
+#include <ctype.h>
 #include "reentrant.h"
 #include "local.h"
 
 /*
+ * Override the file buffering based on the environment setting STDBUF%d
+ * (for the specific file descriptor) and STDBUF (for all descriptors).
+ * the setting is ULB<num> standing for "Unbuffered", "Linebuffered",
+ * and Fullybuffered", and <num> is a value from 0 to 1M
+ */
+static int
+__senvbuf(FILE *fp, size_t *size, int *couldbetty)
+{
+	char evb[64], *evp;
+	int flags, e;
+	intmax_t s;
+
+	flags = 0;
+	if (snprintf(evb, sizeof(evb), "STDBUF%d", fp->_file) < 0)
+		return flags;
+
+	if ((evp = getenv(evb)) == NULL && (evp = getenv("STDBUF")) == NULL)
+		return flags;
+
+	switch (*evp) {
+	case 'u':
+	case 'U':
+		evp++;
+		flags |= __SNBF;
+		break;
+	case 'l':
+	case 'L':
+		evp++;
+		flags |= __SLBF;
+		break;
+	case 'f':
+	case 'F':
+		evp++;
+		*couldbetty = 0;
+		break;
+	}
+
+	if (!isdigit((unsigned char)*evp))
+		return flags;
+
+	s = strtoi(evp, NULL, 0, 0, 1024 * 1024, &e);
+	if (e != 0)
+		return flags;
+
+	*size = (size_t)s;
+	if (*size == 0)
+		return __SNBF;
+
+	return flags;
+}
+
+/*
  * Allocate a file buffer, or switch to unbuffered I/O.
  * Per the ANSI C standard, ALL tty devices default to line buffered.
  *
@@ -69,18 +123,21 @@
 
 	_DIAGASSERT(fp != NULL);
 
-	if (fp->_flags & __SNBF) {
-		fp->_bf._base = fp->_p = fp->_nbuf;
-		fp->_bf._size = 1;
-		return;
-	}
+	if (fp->_flags & __SNBF)
+		goto unbuf;
+
 	flags = __swhatbuf(fp, &size, &couldbetty);
-	if ((p = malloc(size)) == NULL) {
-		fp->_flags |= __SNBF;
-		fp->_bf._base = fp->_p = fp->_nbuf;
-		fp->_bf._size = 1;
-		return;
+
+	if ((fp->_flags & (__SLBF|__SNBF|__SMBF)) == 0
+	    && fp->_cookie == fp && fp->_file >= 0) {
+		flags |= __senvbuf(fp, &size, &couldbetty);
+		if (flags & __SNBF)
+			goto unbuf;
 	}
+
+	if ((p = malloc(size)) == NULL)
+		goto unbuf;
+
 	__cleanup = _cleanup;
 	flags |= __SMBF;
 	fp->_bf._base = fp->_p = p;
@@ -89,6 +146,11 @@
 	if (couldbetty && isatty(__sfileno(fp)))
 		flags |= __SLBF;
 	fp->_flags |= flags;
+	return;
+unbuf:
+	fp->_flags |= __SNBF;
+	fp->_bf._base = fp->_p = fp->_nbuf;
+	fp->_bf._size = 1;
 }
 
 /*
Index: setbuf.3
===================================================================
RCS file: /cvsroot/src/lib/libc/stdio/setbuf.3,v
retrieving revision 1.13
diff -u -u -r1.13 setbuf.3
--- setbuf.3	7 Aug 2003 16:43:31 -0000	1.13
+++ setbuf.3	14 Jul 2015 20:16:45 -0000
@@ -63,6 +63,27 @@
 when it is line buffered characters are saved up until a newline is
 output or input is read from any stream attached to a terminal device
 (typically stdin).
+.Pp
+The default buffer settings can be overwritten per descriptor
+.Dv ( STDBUFn )
+where
+.Dv n
+is the numeric value of the file descriptor represented by the stream, or
+for all descriptors
+.Dv ( STDBUF ) .
+The environment variable value is a letter followed by an optional numeric
+value indicating the size of the buffer.
+Valid sizes range from 0B to 1MB.
+Valid letters are:
+.Bl -tag -width X -indent
+.It Dv Li U
+Unbuffered.
+.It Dv Li L
+Line-buffered.
+.It Dv Li F
+Fully-buffered.
+.El
+.Pp
 The function
 .Xr fflush 3
 may be used to force the block out early.