Date: Sat, 19 Feb 2011 19:50:43 +0100 From: Jeremie Le Hen <jeremie@le-hen.org> To: freebsd-current@FreeBSD.org Subject: [RFC] Force stdio output streams to line-buffered mode Message-ID: <20110219185043.GA6573@felucia.tataz.chchile.org>
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Hi,
I've been annoyed multiple time when running a command such like
iostat -x 1 | grep -v ad10 | cat -n
The problem stems from two factors:
- grep's stdio sees that its stdout is not a terminal, so stdout is
full buffered and not line-buffered;
- iostat produces output too slowly so the aforementioned buffer takes
numerous seconds to be filled and flushed to the last command.
This problems is not specific to FreeBSD, it is actually a consequence
of POSIX specification. I've checked this on Solaris and Linux.
I've attached a small patch for stdio, so if the environment variable
STDIO_IOLBF is set, the output streams will be line-oriented by default.
iostat -x 1 | env STDIO_IOLBF=1 grep -v ad10 | cat -n
Before send it as a PR, I would like to hear your comments about this,
especially:
- the variable name (no bikeshed please, I just ask this if there is a
naming convention I'm not aware of);
- the documentation: I've put a hint in stdio(3) manpage and put the
full explanation in setvbuf(3).
Thanks.
Regards,
--
Jeremie Le Hen
Humans are born free and equal. But some are more equal than others.
Coluche
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diff -rup /usr/src.orig/lib/libc/stdio/makebuf.c /usr/src/lib/libc/stdio/makebuf.c
--- /usr/src.orig/lib/libc/stdio/makebuf.c 2009-08-03 10:13:06.000000000 +0200
+++ /usr/src/lib/libc/stdio/makebuf.c 2011-02-19 19:09:56.000000000 +0100
@@ -59,6 +59,7 @@ __smakebuf(fp)
FILE *fp;
{
void *p;
+ char *bmode;
int flags;
size_t size;
int couldbetty;
@@ -79,7 +80,8 @@ __smakebuf(fp)
flags |= __SMBF;
fp->_bf._base = fp->_p = p;
fp->_bf._size = size;
- if (couldbetty && isatty(fp->_file))
+ if (((bmode = getenv("STDIO_IOLBF")) && bmode[0] != '\0') ||
+ (couldbetty && isatty(fp->_file)))
flags |= __SLBF;
fp->_flags |= flags;
}
diff -rup /usr/src.orig/lib/libc/stdio/setbuf.3 /usr/src/lib/libc/stdio/setbuf.3
--- /usr/src.orig/lib/libc/stdio/setbuf.3 2009-08-03 10:13:06.000000000 +0200
+++ /usr/src/lib/libc/stdio/setbuf.3 2011-02-19 19:09:13.000000000 +0100
@@ -79,7 +79,9 @@ and an optimally-sized buffer is obtaine
If a stream refers to a terminal
(as
.Dv stdout
-normally does) it is line buffered.
+normally does), or the environment variable
+.Ev STDIO_IOLBF
+is set, it is line buffered.
The standard error stream
.Dv stderr
is always unbuffered.
@@ -176,6 +178,12 @@ The
function returns what the equivalent
.Fn setvbuf
would have returned.
+.Sh ENVIRONMENT
+.Bl -tag -width ".Ev STDIO_IOLBF"
+If the environment variable
+.Ev STDIO_IOLBF
+is set, output streams will be line-buffered by default
+even when not referring to a terminal.
.Sh SEE ALSO
.Xr fclose 3 ,
.Xr fopen 3 ,
diff -rup /usr/src.orig/lib/libc/stdio/stdio.3 /usr/src/lib/libc/stdio/stdio.3
--- /usr/src.orig/lib/libc/stdio/stdio.3 2009-08-03 10:13:06.000000000 +0200
+++ /usr/src/lib/libc/stdio/stdio.3 2011-02-19 12:56:00.000000000 +0100
@@ -137,7 +137,8 @@ an interactive or
.Dq terminal
device, as determined by the
.Xr isatty 3
-function.
+function (this can be overriden with an environment variable, see
+.Xr setvbuf 3 ) .
In fact,
.Em all
freshly-opened streams that refer to terminal devices
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