busybox/coreutils/tail.c
Denys Vlasenko f560422fa0 Big cleanup in config help and description
Redundant help texts (one which only repeats the description)
are deleted.

Descriptions and help texts are trimmed.

Some config options are moved, even across menus.

No config option _names_ are changed.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2017-01-10 14:58:54 +01:00

405 lines
10 KiB
C

/* vi: set sw=4 ts=4: */
/*
* Mini tail implementation for busybox
*
* Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
*/
/* Mar 16, 2003 Manuel Novoa III (mjn3@codepoet.org)
*
* Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
* Bugs fixed (although I may have forgotten one or two... it was pretty bad)
* 1) mixing printf/write without fflush()ing stdout
* 2) no check that any open files are present
* 3) optstring had -q taking an arg
* 4) no error checking on write in some cases, and a warning even then
* 5) q and s interaction bug
* 6) no check for lseek error
* 7) lseek attempted when count==0 even if arg was +0 (from top)
*/
//config:config TAIL
//config: bool "tail"
//config: default y
//config: help
//config: tail is used to print the last specified number of lines
//config: from files.
//config:
//config:config FEATURE_FANCY_TAIL
//config: bool "Enable -q, -s, -v, and -F options"
//config: default y
//config: depends on TAIL
//config: help
//config: These options are provided by GNU tail, but
//config: are not specific in the SUSv3 standard:
//config: -q Never output headers giving file names
//config: -s SEC Wait SEC seconds between reads with -f
//config: -v Always output headers giving file names
//config: -F Same as -f, but keep retrying
//applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_TAIL) += tail.o
/* BB_AUDIT SUSv3 compliant (need fancy for -c) */
/* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
/* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
//usage:#define tail_trivial_usage
//usage: "[OPTIONS] [FILE]..."
//usage:#define tail_full_usage "\n\n"
//usage: "Print last 10 lines of each FILE (or stdin) to stdout.\n"
//usage: "With more than one FILE, precede each with a filename header.\n"
//usage: "\n -f Print data as file grows"
//usage: "\n -c [+]N[kbm] Print last N bytes"
//usage: "\n -n N[kbm] Print last N lines"
//usage: "\n -n +N[kbm] Start on Nth line and print the rest"
//usage: IF_FEATURE_FANCY_TAIL(
//usage: "\n -q Never print headers"
//usage: "\n -s SECONDS Wait SECONDS between reads with -f"
//usage: "\n -v Always print headers"
//usage: "\n -F Same as -f, but keep retrying"
//usage: "\n"
//usage: "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
//usage: )
//usage:
//usage:#define tail_example_usage
//usage: "$ tail -n 1 /etc/resolv.conf\n"
//usage: "nameserver 10.0.0.1\n"
#include "libbb.h"
#include "common_bufsiz.h"
struct globals {
bool from_top;
bool exitcode;
} FIX_ALIASING;
#define G (*(struct globals*)bb_common_bufsiz1)
#define INIT_G() do { setup_common_bufsiz(); } while (0)
static void tail_xprint_header(const char *fmt, const char *filename)
{
if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
bb_perror_nomsg_and_die();
}
static ssize_t tail_read(int fd, char *buf, size_t count)
{
ssize_t r;
r = full_read(fd, buf, count);
if (r < 0) {
bb_perror_msg(bb_msg_read_error);
G.exitcode = EXIT_FAILURE;
}
return r;
}
#define header_fmt_str "\n==> %s <==\n"
static unsigned eat_num(const char *p)
{
if (*p == '-')
p++;
else if (*p == '+') {
p++;
G.from_top = 1;
}
return xatou_sfx(p, bkm_suffixes);
}
int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int tail_main(int argc, char **argv)
{
unsigned count = 10;
unsigned sleep_period = 1;
const char *str_c, *str_n;
char *tailbuf;
size_t tailbufsize;
unsigned header_threshhold = 1;
unsigned nfiles;
int i, opt;
int *fds;
const char *fmt;
int prev_fd;
INIT_G();
#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
/* Allow legacy syntax of an initial numeric option without -n. */
if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
&& isdigit(argv[1][1])
) {
count = eat_num(argv[1]);
argv++;
argc--;
}
#endif
/* -s NUM, -F imlies -f */
IF_FEATURE_FANCY_TAIL(opt_complementary = "Ff";)
opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:+vF"),
&str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
#define FOLLOW (opt & 0x1)
#define COUNT_BYTES (opt & 0x2)
//if (opt & 0x1) // -f
if (opt & 0x2) count = eat_num(str_c); // -c
if (opt & 0x4) count = eat_num(str_n); // -n
#if ENABLE_FEATURE_FANCY_TAIL
/* q: make it impossible for nfiles to be > header_threshhold */
if (opt & 0x8) header_threshhold = UINT_MAX; // -q
//if (opt & 0x10) // -s
if (opt & 0x20) header_threshhold = 0; // -v
# define FOLLOW_RETRY (opt & 0x40)
#else
# define FOLLOW_RETRY 0
#endif
argc -= optind;
argv += optind;
/* open all the files */
fds = xmalloc(sizeof(fds[0]) * (argc + 1));
if (!argv[0]) {
struct stat statbuf;
if (fstat(STDIN_FILENO, &statbuf) == 0
&& S_ISFIFO(statbuf.st_mode)
) {
opt &= ~1; /* clear FOLLOW */
}
argv[0] = (char *) bb_msg_standard_input;
}
nfiles = i = 0;
do {
int fd = open_or_warn_stdin(argv[i]);
if (fd < 0 && !FOLLOW_RETRY) {
G.exitcode = EXIT_FAILURE;
continue;
}
fds[nfiles] = fd;
argv[nfiles++] = argv[i];
} while (++i < argc);
if (!nfiles)
bb_error_msg_and_die("no files");
/* prepare the buffer */
tailbufsize = BUFSIZ;
if (!G.from_top && COUNT_BYTES) {
if (tailbufsize < count + BUFSIZ) {
tailbufsize = count + BUFSIZ;
}
}
/* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
* (In fact, it doesn't need ANY memory). So delay allocation.
*/
tailbuf = NULL;
/* tail the files */
fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
i = 0;
do {
char *buf;
int taillen;
int newlines_seen;
unsigned seen;
int nread;
int fd = fds[i];
if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
continue; /* may happen with -F */
if (nfiles > header_threshhold) {
tail_xprint_header(fmt, argv[i]);
fmt = header_fmt_str;
}
if (!G.from_top) {
off_t current = lseek(fd, 0, SEEK_END);
if (current > 0) {
unsigned off;
if (COUNT_BYTES) {
/* Optimizing count-bytes case if the file is seekable.
* Beware of backing up too far.
* Also we exclude files with size 0 (because of /proc/xxx) */
if (count == 0)
continue; /* showing zero bytes is easy :) */
current -= count;
if (current < 0)
current = 0;
xlseek(fd, current, SEEK_SET);
bb_copyfd_size(fd, STDOUT_FILENO, count);
continue;
}
#if 1 /* This is technically incorrect for *LONG* strings, but very useful */
/* Optimizing count-lines case if the file is seekable.
* We assume the lines are <64k.
* (Users complain that tail takes too long
* on multi-gigabyte files) */
off = (count | 0xf); /* for small counts, be more paranoid */
if (off > (INT_MAX / (64*1024)))
off = (INT_MAX / (64*1024));
current -= off * (64*1024);
if (current < 0)
current = 0;
xlseek(fd, current, SEEK_SET);
#endif
}
}
if (!tailbuf)
tailbuf = xmalloc(tailbufsize);
buf = tailbuf;
taillen = 0;
/* "We saw 1st line/byte".
* Used only by +N code ("start from Nth", 1-based): */
seen = 1;
newlines_seen = 0;
while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
if (G.from_top) {
int nwrite = nread;
if (seen < count) {
/* We need to skip a few more bytes/lines */
if (COUNT_BYTES) {
nwrite -= (count - seen);
seen += nread;
} else {
char *s = buf;
do {
--nwrite;
if (*s++ == '\n' && ++seen == count) {
break;
}
} while (nwrite);
}
}
if (nwrite > 0)
xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
} else if (count) {
if (COUNT_BYTES) {
taillen += nread;
if (taillen > (int)count) {
memmove(tailbuf, tailbuf + taillen - count, count);
taillen = count;
}
} else {
int k = nread;
int newlines_in_buf = 0;
do { /* count '\n' in last read */
k--;
if (buf[k] == '\n') {
newlines_in_buf++;
}
} while (k);
if (newlines_seen + newlines_in_buf < (int)count) {
newlines_seen += newlines_in_buf;
taillen += nread;
} else {
int extra = (buf[nread-1] != '\n');
char *s;
k = newlines_seen + newlines_in_buf + extra - count;
s = tailbuf;
while (k) {
if (*s == '\n') {
k--;
}
s++;
}
taillen += nread - (s - tailbuf);
memmove(tailbuf, s, taillen);
newlines_seen = count - extra;
}
if (tailbufsize < (size_t)taillen + BUFSIZ) {
tailbufsize = taillen + BUFSIZ;
tailbuf = xrealloc(tailbuf, tailbufsize);
}
}
buf = tailbuf + taillen;
}
} /* while (tail_read() > 0) */
if (!G.from_top) {
xwrite(STDOUT_FILENO, tailbuf, taillen);
}
} while (++i < nfiles);
prev_fd = fds[i-1];
tailbuf = xrealloc(tailbuf, BUFSIZ);
fmt = NULL;
if (FOLLOW) while (1) {
sleep(sleep_period);
i = 0;
do {
int nread;
const char *filename = argv[i];
int fd = fds[i];
if (FOLLOW_RETRY) {
struct stat sbuf, fsbuf;
if (fd < 0
|| fstat(fd, &fsbuf) < 0
|| stat(filename, &sbuf) < 0
|| fsbuf.st_dev != sbuf.st_dev
|| fsbuf.st_ino != sbuf.st_ino
) {
int new_fd;
if (fd >= 0)
close(fd);
new_fd = open(filename, O_RDONLY);
if (new_fd >= 0) {
bb_error_msg("%s has %s; following end of new file",
filename, (fd < 0) ? "appeared" : "been replaced"
);
} else if (fd >= 0) {
bb_perror_msg("%s has become inaccessible", filename);
}
fds[i] = fd = new_fd;
}
}
if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
continue;
if (nfiles > header_threshhold) {
fmt = header_fmt_str;
}
for (;;) {
/* tail -f keeps following files even if they are truncated */
struct stat sbuf;
/* /proc files report zero st_size, don't lseek them */
if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
off_t current = lseek(fd, 0, SEEK_CUR);
if (sbuf.st_size < current)
xlseek(fd, 0, SEEK_SET);
}
nread = tail_read(fd, tailbuf, BUFSIZ);
if (nread <= 0)
break;
if (fmt && (fd != prev_fd)) {
tail_xprint_header(fmt, filename);
fmt = NULL;
prev_fd = fd;
}
xwrite(STDOUT_FILENO, tailbuf, nread);
}
} while (++i < nfiles);
} /* while (1) */
if (ENABLE_FEATURE_CLEAN_UP) {
free(fds);
free(tailbuf);
}
return G.exitcode;
}