+int copy_file(const char *from, const char *to) {
+ int r, fdf, fdt;
+
+ assert(from);
+ assert(to);
+
+ fdf = open(from, O_RDONLY|O_CLOEXEC|O_NOCTTY);
+ if (fdf < 0)
+ return -errno;
+
+ fdt = open(to, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC|O_NOCTTY, 0644);
+ if (fdt < 0) {
+ close_nointr_nofail(fdf);
+ return -errno;
+ }
+
+ for (;;) {
+ char buf[PIPE_BUF];
+ ssize_t n, k;
+
+ n = read(fdf, buf, sizeof(buf));
+ if (n < 0) {
+ r = -errno;
+
+ close_nointr_nofail(fdf);
+ close_nointr(fdt);
+ unlink(to);
+
+ return r;
+ }
+
+ if (n == 0)
+ break;
+
+ errno = 0;
+ k = loop_write(fdt, buf, n, false);
+ if (n != k) {
+ r = k < 0 ? k : (errno ? -errno : -EIO);
+
+ close_nointr_nofail(fdf);
+ close_nointr(fdt);
+
+ unlink(to);
+ return r;
+ }
+ }
+
+ close_nointr_nofail(fdf);
+ r = close_nointr(fdt);
+
+ if (r < 0) {
+ unlink(to);
+ return r;
+ }
+
+ return 0;
+}
+
+int symlink_or_copy(const char *from, const char *to) {
+ char *pf = NULL, *pt = NULL;
+ struct stat a, b;
+ int r;
+
+ assert(from);
+ assert(to);
+
+ if (parent_of_path(from, &pf) < 0 ||
+ parent_of_path(to, &pt) < 0) {
+ r = -ENOMEM;
+ goto finish;
+ }
+
+ if (stat(pf, &a) < 0 ||
+ stat(pt, &b) < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ if (a.st_dev != b.st_dev) {
+ free(pf);
+ free(pt);
+
+ return copy_file(from, to);
+ }
+
+ if (symlink(from, to) < 0) {
+ r = -errno;
+ goto finish;
+ }
+
+ r = 0;
+
+finish:
+ free(pf);
+ free(pt);
+
+ return r;
+}
+
+int symlink_or_copy_atomic(const char *from, const char *to) {
+ char *t, *x;
+ const char *fn;
+ size_t k;
+ unsigned long long ull;
+ unsigned i;
+ int r;
+
+ assert(from);
+ assert(to);
+
+ t = new(char, strlen(to) + 1 + 16 + 1);
+ if (!t)
+ return -ENOMEM;
+
+ fn = file_name_from_path(to);
+ k = fn-to;
+ memcpy(t, to, k);
+ t[k] = '.';
+ x = stpcpy(t+k+1, fn);
+
+ ull = random_ull();
+ for (i = 0; i < 16; i++) {
+ *(x++) = hexchar(ull & 0xF);
+ ull >>= 4;
+ }
+
+ *x = 0;
+
+ r = symlink_or_copy(from, t);
+ if (r < 0) {
+ unlink(t);
+ free(t);
+ return r;
+ }
+
+ if (rename(t, to) < 0) {
+ r = -errno;
+ unlink(t);
+ free(t);
+ return r;
+ }
+
+ free(t);
+ return r;
+}
+