91b7d6dc58
- Issue a single writev(2) call instead of multiple write(2)s.
This change improves the inefficiencies introduced when echo
went on an stdio diet.
The following figures are for echoing 1000 arguments.
original stdio-based echo:
0.01 real 0.01 user 0.00 sys
before:
0.05 real 0.00 user 0.04 sys
after:
0.01 real 0.00 user 0.00 sys
142 lines
4.1 KiB
C
142 lines
4.1 KiB
C
/*
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* Copyright (c) 1989, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#if 0
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#ifndef lint
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static char const copyright[] =
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"@(#) Copyright (c) 1989, 1993\n\
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The Regents of the University of California. All rights reserved.\n";
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#endif /* not lint */
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#ifndef lint
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static char sccsid[] = "@(#)echo.c 8.1 (Berkeley) 5/31/93";
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#endif /* not lint */
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#endif
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/uio.h>
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#include <assert.h>
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#include <errno.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <string.h>
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#include <unistd.h>
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/*
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* Report an error and exit.
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* Use it instead of err(3) to avoid linking-in stdio.
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*/
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static void
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errexit(const char *prog, const char *reason)
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{
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char *errstr = strerror(errno);
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write(STDERR_FILENO, prog, strlen(prog));
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write(STDERR_FILENO, ": ", 2);
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write(STDERR_FILENO, reason, strlen(reason));
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write(STDERR_FILENO, ": ", 2);
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write(STDERR_FILENO, errstr, strlen(errstr));
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write(STDERR_FILENO, "\n", 1);
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exit(1);
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}
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int
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main(int argc, char *argv[])
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{
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int nflag; /* if not set, output a trailing newline. */
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int veclen; /* number of writev arguments. */
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struct iovec *iov, *vp; /* Elements to write, current element. */
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char space[] = " ";
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char newline[] = "\n";
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char *progname = argv[0];
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/* This utility may NOT do getopt(3) option parsing. */
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if (*++argv && !strcmp(*argv, "-n")) {
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++argv;
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--argc;
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nflag = 1;
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} else
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nflag = 0;
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veclen = (argc >= 2) ? (argc - 2) * 2 + 1 : 0;
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if ((vp = iov = malloc((veclen + 1) * sizeof(struct iovec))) == NULL)
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errexit(progname, "malloc");
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while (argv[0] != NULL) {
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size_t len;
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len = strlen(argv[0]);
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/*
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* If the next argument is NULL then this is this
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* the last argument, therefore we need to check
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* for a trailing \c.
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*/
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if (argv[1] == NULL) {
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/* is there room for a '\c' and is there one? */
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if (len >= 2 &&
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argv[0][len - 2] == '\\' &&
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argv[0][len - 1] == 'c') {
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/* chop it and set the no-newline flag. */
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len -= 2;
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nflag = 1;
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}
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}
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vp->iov_base = *argv;
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vp++->iov_len = len;
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if (*++argv) {
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vp->iov_base = space;
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vp++->iov_len = 1;
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}
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}
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if (!nflag) {
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veclen++;
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vp->iov_base = newline;
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vp++->iov_len = 1;
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}
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/* assert(veclen == (vp - iov)); */
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while (veclen) {
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int nwrite;
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nwrite = (veclen > IOV_MAX) ? IOV_MAX : veclen;
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if (writev(STDOUT_FILENO, iov, nwrite) == -1)
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errexit(progname, "write");
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iov += nwrite;
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veclen -= nwrite;
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}
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return 0;
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}
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