Re: [hackers] [sbase] [PATCH 07/10] concat: Use plain read/write instead of buffered stdio

From: Silvan Jegen <s.jegen_AT_gmail.com>
Date: Mon, 5 Dec 2016 21:40:25 +0100

On Sun, Dec 04, 2016 at 09:55:09PM -0800, Michael Forney wrote:
> If we are just copying data from one file to another, we don't need to
> fill a complete buffer, just read a chunk at a time, and write it to the
> output.
> ---
> cat.c | 34 ++++++++++------------------------
> libutil/concat.c | 24 ++++++++++++++----------
> libutil/cp.c | 42 ++++++++++++++++--------------------------
> sponge.c | 31 +++++++++++++++++--------------
> text.h | 1 -
> util.h | 1 +
> xinstall.c | 25 ++++++++++++-------------
> 7 files changed, 70 insertions(+), 88 deletions(-)
>
> diff --git a/cat.c b/cat.c
> index e3741aa..55585dd 100644
> --- a/cat.c
> +++ b/cat.c
> _AT_@ -1,22 +1,11 @@
> /* See LICENSE file for copyright and license details. */
> -#include <stdio.h>
> +#include <fcntl.h>
> #include <string.h>
> #include <unistd.h>
>
> -#include "text.h"
> #include "util.h"
>
> static void
> -uconcat(FILE *fp1, const char *s1, FILE *fp2, const char *s2)
> -{
> - int c;
> -
> - setbuf(fp2, NULL);
> - while ((c = getc(fp1)) != EOF)
> - putc(c, fp2);
> -}
> -
> -static void
> usage(void)
> {
> eprintf("usage: %s [-u] [file ...]\n", argv0);
> _AT_@ -25,37 +14,34 @@ usage(void)
> int
> main(int argc, char *argv[])
> {
> - FILE *fp;
> - int ret = 0;
> - void (*cat)(FILE *, const char *, FILE *, const char *) = &concat;
> + int fd, ret = 0;
>
> ARGBEGIN {
> case 'u':
> - cat = &uconcat;
> break;
> default:
> usage();
> } ARGEND
>
> if (!argc) {
> - cat(stdin, "<stdin>", stdout, "<stdout>");
> + if (concat(0, "<stdin>", 1, "<stdout>") < 0)
> + ret = 1;
> } else {
> for (; *argv; argc--, argv++) {
> if (!strcmp(*argv, "-")) {
> *argv = "<stdin>";
> - fp = stdin;
> - } else if (!(fp = fopen(*argv, "r"))) {
> - weprintf("fopen %s:", *argv);
> + fd = 0;
> + } else if ((fd = open(*argv, O_RDONLY)) < 0) {
> + weprintf("open %s:", *argv);
> ret = 1;
> continue;
> }
> - cat(fp, *argv, stdout, "<stdout>");
> - if (fp != stdin && fshut(fp, *argv))
> + if (concat(fd, *argv, 1, "<stdout>") < 0)
> ret = 1;
> + if (fd != 0)
> + close(fd);
> }
> }
>
> - ret |= fshut(stdin, "<stdin>") | fshut(stdout, "<stdout>");
> -
> return ret;
> }
> diff --git a/libutil/concat.c b/libutil/concat.c
> index fad9471..3f617e2 100644
> --- a/libutil/concat.c
> +++ b/libutil/concat.c
> _AT_@ -1,19 +1,23 @@
> /* See LICENSE file for copyright and license details. */
> -#include <stdio.h>
> +#include <unistd.h>
>
> -#include "../text.h"
> #include "../util.h"
>
> -void
> -concat(FILE *fp1, const char *s1, FILE *fp2, const char *s2)
> +int
> +concat(int f1, const char *s1, int f2, const char *s2)
> {
> char buf[BUFSIZ];
> - size_t n;
> + ssize_t n;
>
> - while ((n = fread(buf, 1, sizeof(buf), fp1))) {
> - fwrite(buf, 1, n, fp2);
> -
> - if (feof(fp1) || ferror(fp1) || ferror(fp2))
> - break;
> + while ((n = read(f1, buf, sizeof(buf))) > 0) {
> + if (writeall(f2, buf, n) < 0) {
> + weprintf("write %s:", s2);
> + return -1;
> + }
> + }
> + if (n < 0) {
> + weprintf("read %s:", s1);
> + return -1;
> }
> + return 0;
> }
> diff --git a/libutil/cp.c b/libutil/cp.c
> index c398962..8cd0a7d 100644
> --- a/libutil/cp.c
> +++ b/libutil/cp.c

The stdio.h #include can now also be removed from libutil/cp.c.


> _AT_@ -12,7 +12,6 @@
> #include <utime.h>
>
> #include "../fs.h"
> -#include "../text.h"
> #include "../util.h"
>
> int cp_aflag = 0;
> _AT_@ -27,7 +26,7 @@ int
> cp(const char *s1, const char *s2, int depth)
> {
> DIR *dp;
> - FILE *f1, *f2;
> + int f1, f2;
> struct dirent *d;
> struct stat st;
> struct timespec times[2];
> _AT_@ -112,43 +111,34 @@ cp(const char *s1, const char *s2, int depth)
> return 0;
> }
> } else {
> - if (!(f1 = fopen(s1, "r"))) {
> - weprintf("fopen %s:", s1);
> + if ((f1 = open(s1, O_RDONLY)) < 0) {
> + weprintf("open %s:", s1);
> cp_status = 1;
> return 0;
> }
> - if (!(f2 = fopen(s2, "w"))) {
> - if (cp_fflag) {
> - if (unlink(s2) < 0 && errno != ENOENT) {
> - weprintf("unlink %s:", s2);
> - cp_status = 1;
> - return 0;
> - } else if (!(f2 = fopen(s2, "w"))) {
> - weprintf("fopen %s:", s2);
> - cp_status = 1;
> - return 0;
> - }
> - } else {
> - weprintf("fopen %s:", s2);
> + if ((f2 = creat(s2, st.st_mode)) < 0 && cp_fflag) {
> + if (unlink(s2) < 0 && errno != ENOENT) {
> + weprintf("unlink %s:", s2);
> cp_status = 1;
> return 0;
> }
> + f2 = creat(s2, st.st_mode);
> }
> - concat(f1, s1, f2, s2);
> -
> - /* preserve permissions by default */
> - fchmod(fileno(f2), st.st_mode);
> -
> - if (fclose(f2) == EOF) {
> - weprintf("fclose %s:", s2);
> + if (f2 < 0) {
> + weprintf("creat %s:", s2);
> cp_status = 1;
> return 0;
> }
> - if (fclose(f1) == EOF) {
> - weprintf("fclose %s:", s1);
> + if (concat(f1, s1, f2, s2) < 0) {
> cp_status = 1;
> return 0;
> }
> +
> + /* preserve permissions by default */
> + fchmod(f2, st.st_mode);
> +
> + close(f1);
> + close(f2);
> }
>
> if (cp_aflag || cp_pflag) {
> diff --git a/sponge.c b/sponge.c
> index baeac7f..da8b28c 100644
> --- a/sponge.c
> +++ b/sponge.c
> _AT_@ -1,7 +1,8 @@
> /* See LICENSE file for copyright and license details. */
> -#include <stdio.h>
> +#include <fcntl.h>
> +#include <stdlib.h>
> +#include <unistd.h>
>
> -#include "text.h"
> #include "util.h"
>
> static void
> _AT_@ -13,24 +14,26 @@ usage(void)
> int
> main(int argc, char *argv[])
> {
> - FILE *fp, *tmpfp;
> - int ret = 0;
> + char tmp[] = "/tmp/sponge-XXXXXX";
> + int fd, tmpfd;
>
> argv0 = argv[0], argc--, argv++;
>
> if (argc != 1)
> usage();
>
> - if (!(tmpfp = tmpfile()))
> - eprintf("tmpfile:");
> - concat(stdin, "<stdin>", tmpfp, "<tmpfile>");
> - rewind(tmpfp);
> + if ((tmpfd = mkstemp(tmp)) < 0)
> + eprintf("mkstemp:");
> + unlink(tmp);
> + if (concat(0, "<stdin>", tmpfd, "<tmpfile>") < 0)
> + return 1;
> + if (lseek(tmpfd, 0, SEEK_SET) < 0)
> + eprintf("lseek:");
>
> - if (!(fp = fopen(argv[0], "w")))
> - eprintf("fopen %s:", argv[0]);
> - concat(tmpfp, "<tmpfile>", fp, argv[0]);
> + if ((fd = creat(argv[0], 0666)) < 0)

Mode 0660 may be the safer option here.

Other than that it LGTM!


Cheers,

Silvan

> + eprintf("creat %s:", argv[0]);
> + if (concat(tmpfd, "<tmpfile>", fd, argv[0]) < 0)
> + return 1;
>
> - ret |= fshut(fp, argv[0]) | fshut(tmpfp, "<tmpfile>");
> -
> - return ret;
> + return 0;
> }
> diff --git a/text.h b/text.h
> index bceda52..9858592 100644
> --- a/text.h
> +++ b/text.h
> _AT_@ -13,5 +13,4 @@ struct linebuf {
> #define EMPTY_LINEBUF {NULL, 0, 0,}
> void getlines(FILE *, struct linebuf *);
>
> -void concat(FILE *, const char *, FILE *, const char *);
> int linecmp(struct line *, struct line *);
> diff --git a/util.h b/util.h
> index eaad3ce..968a3af 100644
> --- a/util.h
> +++ b/util.h
> _AT_@ -64,6 +64,7 @@ int eregcomp(regex_t *, const char *, int);
>
> /* io */
> ssize_t writeall(int, const void *, size_t);
> +int concat(int, const char *, int, const char *);
>
> /* misc */
> void enmasse(int, char **, int (*)(const char *, const char *, int));
> diff --git a/xinstall.c b/xinstall.c
> index 5a0e390..3d24a1a 100644
> --- a/xinstall.c
> +++ b/xinstall.c
> _AT_@ -2,6 +2,7 @@
> #include <grp.h>
> #include <pwd.h>
> #include <errno.h>
> +#include <fcntl.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <string.h>
> _AT_@ -10,7 +11,6 @@
> #include <sys/wait.h>
>
> #include "util.h"
> -#include "text.h"
>
> static int Dflag = 0;
> static int sflag = 0;
> _AT_@ -61,7 +61,7 @@ static int
> install(const char *s1, const char *s2, int depth)
> {
> DIR *dp;
> - FILE *f1, *f2;
> + int f1, f2;
> struct dirent *d;
> struct stat st;
> ssize_t r;
> _AT_@ -109,23 +109,22 @@ install(const char *s1, const char *s2, int depth)
> else if (mknod(s2, (st.st_mode & ~07777) | mode, st.st_rdev) < 0)
> eprintf("mknod %s:", s2);
> } else {
> - if (!(f1 = fopen(s1, "r")))
> - eprintf("fopen %s:", s1);
> - if (!(f2 = fopen(s2, "w"))) {
> + if ((f1 = open(s1, O_RDONLY)) < 0)
> + eprintf("open %s:", s1);
> + if ((f2 = creat(s2, 0600)) < 0) {
> if (unlink(s2) < 0 && errno != ENOENT)
> eprintf("unlink %s:", s2);
> - else if (!(f2 = fopen(s2, "w")))
> - eprintf("fopen %s:", s2);
> + if ((f2 = creat(s2, 0600)) < 0)
> + eprintf("creat %s:", s2);
> }
> - concat(f1, s1, f2, s2);
> + if (concat(f1, s1, f2, s2) < 0)
> + exit(1);
>
> - if (fchmod(fileno(f2), mode) < 0)
> + if (fchmod(f2, mode) < 0)
> eprintf("fchmod %s:", s2);
>
> - if (fclose(f2) == EOF)
> - eprintf("fclose %s:", s2);
> - if (fclose(f1) == EOF)
> - eprintf("fclose %s:", s1);
> + close(f1);
> + close(f2);
>
> if (sflag)
> strip(s2);
> --
> 2.11.0
>
>
Received on Mon Dec 05 2016 - 21:40:25 CET