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/*
* simpletail.c
* A fast implementation of tail which uses the inotify-API present in
* recent Linux Kernels.
*
* Copyright (C) 2005-2006, Tobias Klauser <tklauser@access.unizh.ch>
*
* The idea and some code were taken from turbotail.
*
* This program is free software; you can redistribute it and/or modify it under
* the terms of the GNU General Public License as published by the Free Software
* Foundation; either version 2, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
* FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License along with
* this program; if not, write to the Free Software Foundation, Inc., 51
* Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include "inotify.h"
#include "inotify-syscalls.h"
#include "inotail.h"
#define BUFFER_SIZE 4096
void usage(void)
{
fprintf(stderr, "usage: simpletail [-f] [-n <nr-lines>] <file>\n");
exit(EXIT_FAILURE);
}
off_t lines(int fd, int file_size, unsigned int n_lines)
{
int i;
char buf[BUFFER_SIZE];
off_t offset = file_size;
/* Negative offsets don't make sense here */
if (offset < 0)
offset = 0;
while (offset > 0 && n_lines > 0) {
int rc;
int block_size = BUFFER_SIZE; /* Size of the current block we're reading */
if (offset < BUFFER_SIZE)
block_size = offset;
/* Start of current block */
offset -= block_size;
dprintf(" offset: %lu\n", offset);
lseek(fd, offset, SEEK_SET);
rc = read(fd, &buf, block_size);
for (i = block_size; i > 0; i--) {
if (buf[i] == '\n') {
dprintf(" Found \\n at position %d\n", i);
n_lines--;
if (n_lines == 0)
break;
}
}
}
if (n_lines == 0)
offset += i + 1; /* We don't want the first \n */
return offset;
}
int watch_file(const char *filename, off_t offset)
{
int ifd, watch;
struct inotify_event *inev;
char buf[BUFFER_SIZE];
dprintf(">> Watching %s\n", filename);
ifd = inotify_init();
if (ifd < 0) {
perror("inotify_init()");
exit(-2);
}
watch = inotify_add_watch(ifd, filename, IN_MODIFY|IN_DELETE_SELF|IN_MOVE_SELF|IN_UNMOUNT);
memset(&buf, 0, sizeof(buf));
while (1) {
int len;
len = read(ifd, buf, sizeof(buf));
inev = (struct inotify_event *) &buf;
while (len > 0) {
if (inev->mask & IN_MODIFY) {
int ffd, block_size;
char fbuf[BUFFER_SIZE];
struct stat finfo;
dprintf(" File '%s' modified.\n", filename);
dprintf(" offset: %lu.\n", offset);
ffd = open(filename, O_RDONLY);
if (fstat(ffd, &finfo) < 0) {
perror("fstat()");
return -1;
}
/* XXX: block_size could be bigger than BUFFER_SIZE */
block_size = finfo.st_size - offset;
if (block_size < 0)
block_size = 0;
lseek(ffd, offset, SEEK_SET);
while (read(ffd, &fbuf, BUFFER_SIZE) != 0) {
write(STDOUT_FILENO, fbuf, block_size);
}
offset = finfo.st_size;
close(ffd);
}
if (inev->mask & IN_DELETE_SELF) {
dprintf(" File '%s' deleted.\n", filename);
return -1;
}
if (inev->mask & IN_MOVE_SELF) {
dprintf(" File '%s' moved.\n", filename);
return -1;
}
if (inev->mask & IN_UNMOUNT) {
dprintf(" Device containing file '%s' unmounted.\n", filename);
return -1;
}
len -= sizeof(struct inotify_event) + inev->len;
inev = (struct inotify_event *) ((char *) inev + sizeof(struct inotify_event) + inev->len);
}
}
}
int main(int argc, char **argv)
{
int i, fd;
int n_lines = 0;
int ret = 0;
short forever = 0;
char buf[BUFFER_SIZE], *filename;
struct stat finfo;
off_t offset = 0;
if (argc < 3)
usage();
for (i = 1; (i + 1 < argc) && (argv[i][0] == '-'); i++) {
switch (argv[i][1]) {
case 'f':
forever = 1;
break;
case 'n':
n_lines = strtol(argv[++i], NULL, 0) + 1;
break;
default:
usage();
break;
}
}
filename = argv[i];
fd = open(filename, O_RDONLY);
if (fd < 0) {
perror("open()");
return -1;
}
if (fstat(fd, &finfo) < 0) {
perror("fstat()");
return -1;
}
offset = lines(fd, finfo.st_size, n_lines);
dprintf(" offset: %lu.\n", offset);
lseek(fd, offset, SEEK_SET);
while (read(fd, &buf, BUFFER_SIZE) != 0) {
write(STDOUT_FILENO, buf, finfo.st_size - offset);
}
close(fd);
if (forever)
ret = watch_file(filename, finfo.st_size);
return ret;
}
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