return RET_NERRNO(linkat(fd, "", newdirfd, newpath, AT_EMPTY_PATH));
}
+
+int linkat_replace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
+ _cleanup_close_ int old_fd = -EBADF;
+ int r;
+
+ assert(olddirfd >= 0 || olddirfd == AT_FDCWD);
+ assert(newdirfd >= 0 || newdirfd == AT_FDCWD);
+ assert(!isempty(newpath)); /* source path is optional, but the target path is not */
+
+ /* Like linkat() but replaces the target if needed. Is a NOP if source and target already share the
+ * same inode. */
+
+ if (olddirfd == AT_FDCWD && isempty(oldpath)) /* Refuse operating on the cwd (which is a dir, and dirs can't be hardlinked) */
+ return -EISDIR;
+
+ if (path_implies_directory(oldpath)) /* Refuse these definite directories early */
+ return -EISDIR;
+
+ if (path_implies_directory(newpath))
+ return -EISDIR;
+
+ /* First, try to link this directly */
+ if (oldpath)
+ r = RET_NERRNO(linkat(olddirfd, oldpath, newdirfd, newpath, 0));
+ else
+ r = link_fd(olddirfd, newdirfd, newpath);
+ if (r >= 0)
+ return 0;
+ if (r != -EEXIST)
+ return r;
+
+ old_fd = xopenat(olddirfd, oldpath, O_PATH|O_CLOEXEC);
+ if (old_fd < 0)
+ return old_fd;
+
+ struct stat old_st;
+ if (fstat(old_fd, &old_st) < 0)
+ return -errno;
+
+ if (S_ISDIR(old_st.st_mode)) /* Don't bother if we are operating on a directory */
+ return -EISDIR;
+
+ struct stat new_st;
+ if (fstatat(newdirfd, newpath, &new_st, AT_SYMLINK_NOFOLLOW) < 0)
+ return -errno;
+
+ if (S_ISDIR(new_st.st_mode)) /* Refuse replacing directories */
+ return -EEXIST;
+
+ if (stat_inode_same(&old_st, &new_st)) /* Already the same inode? Then shortcut this */
+ return 0;
+
+ _cleanup_free_ char *tmp_path = NULL;
+ r = tempfn_random(newpath, /* extra= */ NULL, &tmp_path);
+ if (r < 0)
+ return r;
+
+ r = link_fd(old_fd, newdirfd, tmp_path);
+ if (r < 0) {
+ if (!ERRNO_IS_PRIVILEGE(r))
+ return r;
+
+ /* If that didn't work due to permissions then go via the path of the dentry */
+ r = RET_NERRNO(linkat(olddirfd, oldpath, newdirfd, tmp_path, 0));
+ if (r < 0)
+ return r;
+ }
+
+ r = RET_NERRNO(renameat(newdirfd, tmp_path, newdirfd, newpath));
+ if (r < 0) {
+ (void) unlinkat(newdirfd, tmp_path, /* flags= */ 0);
+ return r;
+ }
+
+ return 0;
+}
assert_se(xopenat_lock_full(tfd, "def", O_DIRECTORY, 0, 0755, LOCK_POSIX, LOCK_EX) == -EBADF);
}
+TEST(linkat_replace) {
+ _cleanup_(rm_rf_physical_and_freep) char *t = NULL;
+ _cleanup_close_ int tfd = -EBADF;
+
+ assert_se((tfd = mkdtemp_open(NULL, 0, &t)) >= 0);
+
+ _cleanup_close_ int fd1 = openat(tfd, "foo", O_CREAT|O_RDWR|O_CLOEXEC, 0600);
+ assert_se(fd1 >= 0);
+
+ assert_se(linkat_replace(tfd, "foo", tfd, "bar") >= 0);
+ assert_se(linkat_replace(tfd, "foo", tfd, "bar") >= 0);
+
+ _cleanup_close_ int fd1_check = openat(tfd, "bar", O_RDWR|O_CLOEXEC);
+ assert_se(fd1_check >= 0);
+
+ assert_se(inode_same_at(fd1, NULL, fd1_check, NULL, AT_EMPTY_PATH) > 0);
+
+ _cleanup_close_ int fd2 = openat(tfd, "baz", O_CREAT|O_RDWR|O_CLOEXEC, 0600);
+ assert_se(fd2 >= 0);
+
+ assert_se(inode_same_at(fd1, NULL, fd2, NULL, AT_EMPTY_PATH) == 0);
+
+ assert_se(linkat_replace(tfd, "foo", tfd, "baz") >= 0);
+
+ _cleanup_close_ int fd2_check = openat(tfd, "baz", O_RDWR|O_CLOEXEC);
+
+ assert_se(inode_same_at(fd2, NULL, fd2_check, NULL, AT_EMPTY_PATH) == 0);
+ assert_se(inode_same_at(fd1, NULL, fd2_check, NULL, AT_EMPTY_PATH) > 0);
+}
+
static int intro(void) {
arg_test_dir = saved_argv[1];
return EXIT_SUCCESS;