busybox/coreutils/tail.c

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/* vi: set sw=4 ts=4: */
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/*
* 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.
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*/
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/* 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))
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//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"
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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)
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static void tail_xprint_header(const char *fmt, const char *filename)
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{
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if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
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bb_perror_nomsg_and_die();
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}
static ssize_t tail_read(int fd, char *buf, size_t count)
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{
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ssize_t r;
r = full_read(fd, buf, count);
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if (r < 0) {
bb_perror_msg(bb_msg_read_error);
G.exitcode = EXIT_FAILURE;
}
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return r;
}
#define header_fmt_str "\n==> %s <==\n"
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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;
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int tail_main(int argc, char **argv)
{
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unsigned count = 10;
unsigned sleep_period = 1;
const char *str_c, *str_n;
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char *tailbuf;
size_t tailbufsize;
unsigned header_threshhold = 1;
unsigned nfiles;
int i, opt;
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int *fds;
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const char *fmt;
int prev_fd;
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INIT_G();
#if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
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/* 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--;
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}
#endif
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/* -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));
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#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
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if (opt & 0x20) header_threshhold = 0; // -v
# define FOLLOW_RETRY (opt & 0x40)
#else
# define FOLLOW_RETRY 0
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#endif
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argc -= optind;
argv += optind;
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/* open all the files */
fds = xmalloc(sizeof(fds[0]) * (argc + 1));
if (!argv[0]) {
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struct stat statbuf;
if (fstat(STDIN_FILENO, &statbuf) == 0
&& S_ISFIFO(statbuf.st_mode)
) {
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opt &= ~1; /* clear FOLLOW */
}
argv[0] = (char *) bb_msg_standard_input;
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}
nfiles = i = 0;
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do {
int fd = open_or_warn_stdin(argv[i]);
if (fd < 0 && !FOLLOW_RETRY) {
G.exitcode = EXIT_FAILURE;
continue;
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}
fds[nfiles] = fd;
argv[nfiles++] = argv[i];
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} while (++i < argc);
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if (!nfiles)
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bb_error_msg_and_die("no files");
/* prepare the buffer */
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tailbufsize = BUFSIZ;
if (!G.from_top && COUNT_BYTES) {
if (tailbufsize < count + BUFSIZ) {
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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 */
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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 */
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if (nfiles > header_threshhold) {
tail_xprint_header(fmt, argv[i]);
fmt = header_fmt_str;
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}
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);
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buf = tailbuf;
taillen = 0;
/* "We saw 1st line/byte".
* Used only by +N code ("start from Nth", 1-based): */
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seen = 1;
newlines_seen = 0;
while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
if (G.from_top) {
int nwrite = nread;
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if (seen < count) {
/* We need to skip a few more bytes/lines */
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if (COUNT_BYTES) {
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nwrite -= (count - seen);
seen += nread;
} else {
char *s = buf;
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do {
--nwrite;
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if (*s++ == '\n' && ++seen == count) {
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break;
}
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} while (nwrite);
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}
}
if (nwrite > 0)
xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
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} else if (count) {
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if (COUNT_BYTES) {
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taillen += nread;
if (taillen > (int)count) {
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memmove(tailbuf, tailbuf + taillen - count, count);
taillen = count;
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}
} else {
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int k = nread;
int newlines_in_buf = 0;
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do { /* count '\n' in last read */
k--;
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if (buf[k] == '\n') {
newlines_in_buf++;
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}
} while (k);
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if (newlines_seen + newlines_in_buf < (int)count) {
newlines_seen += newlines_in_buf;
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taillen += nread;
} else {
int extra = (buf[nread-1] != '\n');
char *s;
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k = newlines_seen + newlines_in_buf + extra - count;
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s = tailbuf;
while (k) {
if (*s == '\n') {
k--;
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}
s++;
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}
taillen += nread - (s - tailbuf);
memmove(tailbuf, s, taillen);
newlines_seen = count - extra;
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}
if (tailbufsize < (size_t)taillen + BUFSIZ) {
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tailbufsize = taillen + BUFSIZ;
tailbuf = xrealloc(tailbuf, tailbufsize);
}
}
buf = tailbuf + taillen;
}
} /* while (tail_read() > 0) */
if (!G.from_top) {
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xwrite(STDOUT_FILENO, tailbuf, taillen);
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}
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} while (++i < nfiles);
prev_fd = fds[i-1];
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tailbuf = xrealloc(tailbuf, BUFSIZ);
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fmt = NULL;
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if (FOLLOW) while (1) {
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sleep(sleep_period);
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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;
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if (nfiles > header_threshhold) {
fmt = header_fmt_str;
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}
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);
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fmt = NULL;
prev_fd = fd;
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}
xwrite(STDOUT_FILENO, tailbuf, nread);
}
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} while (++i < nfiles);
} /* while (1) */
if (ENABLE_FEATURE_CLEAN_UP) {
free(fds);
free(tailbuf);
}
return G.exitcode;
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}