src/utmpx/utmpx.c

/*	Common utmpx implementation
	Copyright 2015-2023 Rivoreo

	Permission is hereby granted, free of charge, to any person obtaining
	a copy of this software and associated documentation files (the
	"Software"), to deal in the Software without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Software, and to
	permit persons to whom the Software is furnished to do so, subject to
	the following conditions:

	The above copyright notice and this permission notice shall be
	included in all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
	IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
	DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
	OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
	THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/

#define _GNU_SOURCE
#include "utmpx.h"
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <limits.h>

static int utmpx_fd = -1;
static char utmpx_file[PATH_MAX+1] = UTMPX_FILE;

static int open_utmpx() {
	if(utmpx_fd != -1) return utmpx_fd;
	utmpx_fd = open(utmpx_file, O_RDWR);
	return utmpx_fd;
}

void setutxent() {
	if(utmpx_fd == -1) open_utmpx();
	else lseek(utmpx_fd, 0, SEEK_SET);
}

void endutxent() {
	if(utmpx_fd == -1) return;
	close(utmpx_fd);
	utmpx_fd = -1;
}

struct utmpx *getutxent() {
	static struct utmpx buffer;
	if(utmpx_fd == -1 && open_utmpx() == -1) return NULL;
	int s = read(utmpx_fd, &buffer, sizeof buffer);
	if(s < (int)sizeof buffer) return NULL;
	return &buffer;
}

struct utmpx *getutxid(const struct utmpx *id) {
	static struct utmpx buffer;
	if(utmpx_fd == -1 && open_utmpx() == -1) return NULL;
	int s;
	while((s = read(utmpx_fd, &buffer, sizeof buffer))) {
		if(s == -1 && (errno == EINTR || errno == EAGAIN)) continue;
		if(s < (int)sizeof buffer) break;
		switch(id->ut_type) {
			case RUN_LVL:
			case BOOT_TIME:
			case NEW_TIME:
			case OLD_TIME:
				if(id->ut_type == buffer.ut_type) return &buffer;
				break;
			case INIT_PROCESS:
			case LOGIN_PROCESS:
			case USER_PROCESS:
			case DEAD_PROCESS:
				switch(buffer.ut_type) {
					case INIT_PROCESS:
					case LOGIN_PROCESS:
					case USER_PROCESS:
					case DEAD_PROCESS:
						if(memcmp(id->ut_id, buffer.ut_id, sizeof buffer.ut_id) == 0) return &buffer;
						break;
				}
				break;
			default:
				return NULL;
		}
	}
	return NULL;
}

struct utmpx *getutxline(const struct utmpx *line) {
	static struct utmpx buffer;
	if(utmpx_fd == -1 && open_utmpx() == -1) return NULL;
	int s;
	while((s = read(utmpx_fd, &buffer, sizeof buffer))) {
		if(s == -1 && (errno == EINTR || errno == EAGAIN)) continue;
		if(s < (int)sizeof buffer) break;
		switch(buffer.ut_type) {
			case LOGIN_PROCESS:
			case USER_PROCESS:
				if(strncmp(line->ut_line, buffer.ut_line, sizeof buffer.ut_line) == 0) return &buffer;
				break;
		}
	}
	return NULL;
}

static int lock_write_end(int fd, const void *buffer, size_t count) {
	int r, e;
	if(lockf(fd, F_LOCK, 0) < 0) return -1;
	if(lseek(fd, 0, SEEK_END) == (off_t)-1) {
		r = -1;
		e = errno;
		goto end;
	}
	do {
		r = write(fd, buffer, count);
	} while(r < 0 && ((e = errno) == EINTR || e == EAGAIN));
end:
	lockf(fd, F_ULOCK, 0);
	if(r < 0) errno = e;
	return r;
}

struct utmpx *pututxline(const struct utmpx *utx) {
	static struct utmpx buffer;
	if(!utx) {
		errno = EFAULT;
		return NULL;
	}
	//if(utmpx_fd == -1 && open_utmpx() == -1) return NULL;
	setutxent();
	if(utmpx_fd == -1) return NULL;
	memcpy(&buffer, utx, sizeof buffer);
	struct utmpx *old = getutxid(utx);
	if(old) {
		lseek(utmpx_fd, -(off_t)sizeof buffer, SEEK_CUR);
		int s;
		do {
			s = write(utmpx_fd, &buffer, sizeof buffer);
		} while(s == -1 && (errno == EINTR || errno == EAGAIN));
		if(s < 0) return NULL;
	} else if(lock_write_end(utmpx_fd, &buffer, sizeof buffer) < 0) {
		return NULL;
	}
	return &buffer;
}

#undef utmpxname
int utmpxname(const char *name) {
	if(!name) {
		errno = EFAULT;
		return -1;
	}
	size_t len = strlen(name) + 1;
	if(len > sizeof utmpx_file) {
		errno = ENAMETOOLONG;
		return -1;
	}
	memcpy(utmpx_file, name, len);
	return 0;
}