text: /*
   * Portable xxxat() functions.
   *
   * Copyright (C) 2010 Karel Zak <kzak@redhat.com>
   */
  #include <stdio.h>
  #include <stdlib.h>
  #include <fcntl.h>
  #include <sys/stat.h>
  
  #include "at.h"
  #include "c.h"
  
  #ifdef HAVE_FSTATAT
  int fstat_at(int dir, const char *dirname __attribute__ ((__unused__)),
  	     const char *filename, struct stat *st, int nofollow)
  {
  	return fstatat(dir, filename, st,
  			nofollow ? AT_SYMLINK_NOFOLLOW : 0);
  }
  #else
  int fstat_at(int dir, const char *dirname, const char *filename,
  				struct stat *st, int nofollow)
  {
  
  	if (*filename != '/') {
  		char path[PATH_MAX];
  		int len;
  
  		len = snprintf(path, sizeof(path), "%s/%s", dirname, filename);
  		if (len < 0 || len + 1 > sizeof(path))
  			return -1;
  
  		return nofollow ? lstat(path, st) : stat(path, st);
  	}
  
  	return nofollow ? lstat(filename, st) : stat(filename, st);
  }
  #endif
  
  #ifdef HAVE_FSTATAT
  int open_at(int dir, const char *dirname __attribute__ ((__unused__)),
  	    const char *filename, int flags)
  {
  	return openat(dir, filename, flags);
  }
  #else
  int open_at(int dir, const char *dirname, const char *filename, int flags)
  {
  	if (*filename != '/') {
  		char path[PATH_MAX];
  		int len;
  
  		len = snprintf(path, sizeof(path), "%s/%s", dirname, filename);
  		if (len < 0 || len + 1 > sizeof(path))
  			return -1;
  
  		return open(path, flags);
  	}
  	return open(filename, flags);
  }
  #endif
  
  FILE *fopen_at(int dir, const char *dirname, const char *filename, int flags,
  			const char *mode)
  {
  	int fd = open_at(dir, dirname, filename, flags);
  
  	if (fd < 0)
  		return NULL;
  
  	return fdopen(fd, mode);
  }
  
  #ifdef HAVE_FSTATAT
  ssize_t readlink_at(int dir, const char *dirname __attribute__ ((__unused__)),
  		    const char *pathname, char *buf, size_t bufsiz)
  {
  	return readlinkat(dir, pathname, buf, bufsiz);
  }
  #else
  ssize_t readlink_at(int dir, const char *dirname, const char *pathname,
  		    char *buf, size_t bufsiz)
  {
  	if (*pathname != '/') {
  		char path[PATH_MAX];
  		int len;
  
  		len = snprintf(path, sizeof(path), "%s/%s", dirname, pathname);
  		if (len < 0 || len + 1 > sizeof(path))
  			return -1;
  
  		return readlink(path, buf, bufsiz);
  	}
  	return readlink(pathname, buf, bufsiz);
  }
  #endif
  
  #ifdef TEST_PROGRAM_AT
  #include <errno.h>
  #include <sys/types.h>
  #include <dirent.h>
  #include <string.h>
  
  int main(int argc, char *argv[])
  {
  	DIR *dir;
  	struct dirent *d;
  	char *dirname;
  
  	if (argc != 2) {
  		fprintf(stderr, "usage: %s <directory>\n", argv[0]);
  		exit(EXIT_FAILURE);
  	}
  	dirname = argv[1];
  
  	dir = opendir(dirname);
  	if (!dir)
  		err(EXIT_FAILURE, "%s: open failed", dirname);
  
  	while ((d = readdir(dir))) {
  		struct stat st;
  		FILE *f;
  
  		printf("%32s ", d->d_name);
  
  		if (fstat_at(dirfd(dir), dirname, d->d_name, &st, 0) == 0)
  			printf("%16jd bytes ", st.st_size);
  		else
  			printf("%16s bytes ", "???");
  
  		f = fopen_at(dirfd(dir), dirname, d->d_name, O_RDONLY, "r");
  		printf("   %s\n", f ? "OK" : strerror(errno));
  		if (f)
  			fclose(f);
  	}
  	closedir(dir);
  	return EXIT_SUCCESS;
  }
  #endif
  