Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1238 insertions, 0 deletions

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
new file mode 100644
index 0000000..9ba9268
--- /dev/null
+++ b/src/basic/fs-util.c
@@ -0,0 +1,1238 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <sys/file.h>
+#include <linux/falloc.h>
+#include <linux/magic.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "btrfs.h"
+#include "dirent-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "hostname-util.h"
+#include "label.h"
+#include "lock-util.h"
+#include "log.h"
+#include "macro.h"
+#include "missing_fcntl.h"
+#include "missing_fs.h"
+#include "missing_syscall.h"
+#include "mkdir.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "random-util.h"
+#include "ratelimit.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "time-util.h"
+#include "tmpfile-util.h"
+#include "umask-util.h"
+#include "user-util.h"
+
+int rmdir_parents(const char *path, const char *stop) {
+        char *p;
+        int r;
+
+        assert(path);
+        assert(stop);
+
+        if (!path_is_safe(path))
+                return -EINVAL;
+
+        if (!path_is_safe(stop))
+                return -EINVAL;
+
+        p = strdupa_safe(path);
+
+        for (;;) {
+                char *slash = NULL;
+
+                /* skip the last component. */
+                r = path_find_last_component(p, /* accept_dot_dot= */ false, (const char **) &slash, NULL);
+                if (r <= 0)
+                        return r;
+                if (slash == p)
+                        return 0;
+
+                assert(*slash == '/');
+                *slash = '\0';
+
+                if (path_startswith_full(stop, p, /* accept_dot_dot= */ false))
+                        return 0;
+
+                if (rmdir(p) < 0 && errno != ENOENT)
+                        return -errno;
+        }
+}
+
+int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
+        int r;
+
+        /* Try the ideal approach first */
+        if (renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE) >= 0)
+                return 0;
+
+        /* renameat2() exists since Linux 3.15, btrfs and FAT added support for it later. If it is not implemented,
+         * fall back to a different method. */
+        if (!ERRNO_IS_NOT_SUPPORTED(errno) && errno != EINVAL)
+                return -errno;
+
+        /* Let's try to use linkat()+unlinkat() as fallback. This doesn't work on directories and on some file systems
+         * that do not support hard links (such as FAT, most prominently), but for files it's pretty close to what we
+         * want — though not atomic (i.e. for a short period both the new and the old filename will exist). */
+        if (linkat(olddirfd, oldpath, newdirfd, newpath, 0) >= 0) {
+
+                r = RET_NERRNO(unlinkat(olddirfd, oldpath, 0));
+                if (r < 0) {
+                        (void) unlinkat(newdirfd, newpath, 0);
+                        return r;
+                }
+
+                return 0;
+        }
+
+        if (!ERRNO_IS_NOT_SUPPORTED(errno) && !IN_SET(errno, EINVAL, EPERM)) /* FAT returns EPERM on link()… */
+                return -errno;
+
+        /* OK, neither RENAME_NOREPLACE nor linkat()+unlinkat() worked. Let's then fall back to the racy TOCTOU
+         * vulnerable accessat(F_OK) check followed by classic, replacing renameat(), we have nothing better. */
+
+        if (faccessat(newdirfd, newpath, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
+                return -EEXIST;
+        if (errno != ENOENT)
+                return -errno;
+
+        return RET_NERRNO(renameat(olddirfd, oldpath, newdirfd, newpath));
+}
+
+int readlinkat_malloc(int fd, const char *p, char **ret) {
+        size_t l = PATH_MAX;
+
+        assert(fd >= 0 || fd == AT_FDCWD);
+
+        if (fd < 0 && isempty(p))
+                return -EISDIR; /* In this case, the fd points to the current working directory, and is
+                                 * definitely not a symlink. Let's return earlier. */
+
+        for (;;) {
+                _cleanup_free_ char *c = NULL;
+                ssize_t n;
+
+                c = new(char, l+1);
+                if (!c)
+                        return -ENOMEM;
+
+                n = readlinkat(fd, strempty(p), c, l);
+                if (n < 0)
+                        return -errno;
+
+                if ((size_t) n < l) {
+                        c[n] = 0;
+
+                        if (ret)
+                                *ret = TAKE_PTR(c);
+
+                        return 0;
+                }
+
+                if (l > (SSIZE_MAX-1)/2) /* readlinkat() returns an ssize_t, and we want an extra byte for a
+                                          * trailing NUL, hence do an overflow check relative to SSIZE_MAX-1
+                                          * here */
+                        return -EFBIG;
+
+                l *= 2;
+        }
+}
+
+int readlink_malloc(const char *p, char **ret) {
+        return readlinkat_malloc(AT_FDCWD, p, ret);
+}
+
+int readlink_value(const char *p, char **ret) {
+        _cleanup_free_ char *link = NULL, *name = NULL;
+        int r;
+
+        assert(p);
+        assert(ret);
+
+        r = readlink_malloc(p, &link);
+        if (r < 0)
+                return r;
+
+        r = path_extract_filename(link, &name);
+        if (r < 0)
+                return r;
+        if (r == O_DIRECTORY)
+                return -EINVAL;
+
+        *ret = TAKE_PTR(name);
+        return 0;
+}
+
+int readlink_and_make_absolute(const char *p, char **ret) {
+        _cleanup_free_ char *target = NULL;
+        int r;
+
+        assert(p);
+        assert(ret);
+
+        r = readlink_malloc(p, &target);
+        if (r < 0)
+                return r;
+
+        return file_in_same_dir(p, target, ret);
+}
+
+int chmod_and_chown_at(int dir_fd, const char *path, mode_t mode, uid_t uid, gid_t gid) {
+        _cleanup_close_ int fd = -EBADF;
+
+        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+
+        if (path) {
+                /* Let's acquire an O_PATH fd, as precaution to change mode/owner on the same file */
+                fd = openat(dir_fd, path, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+                if (fd < 0)
+                        return -errno;
+                dir_fd = fd;
+
+        } else if (dir_fd == AT_FDCWD) {
+                /* Let's acquire an O_PATH fd of the current directory */
+                fd = openat(dir_fd, ".", O_PATH|O_CLOEXEC|O_NOFOLLOW|O_DIRECTORY);
+                if (fd < 0)
+                        return -errno;
+                dir_fd = fd;
+        }
+
+        return fchmod_and_chown(dir_fd, mode, uid, gid);
+}
+
+int fchmod_and_chown_with_fallback(int fd, const char *path, mode_t mode, uid_t uid, gid_t gid) {
+        bool do_chown, do_chmod;
+        struct stat st;
+        int r;
+
+        /* Change ownership and access mode of the specified fd. Tries to do so safely, ensuring that at no
+         * point in time the access mode is above the old access mode under the old ownership or the new
+         * access mode under the new ownership. Note: this call tries hard to leave the access mode
+         * unaffected if the uid/gid is changed, i.e. it undoes implicit suid/sgid dropping the kernel does
+         * on chown().
+         *
+         * This call is happy with O_PATH fds.
+         *
+         * If path is given, allow a fallback path which does not use /proc/self/fd/. On any normal system
+         * /proc will be mounted, but in certain improperly assembled environments it might not be. This is
+         * less secure (potential TOCTOU), so should only be used after consideration. */
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        do_chown =
+                (uid != UID_INVALID && st.st_uid != uid) ||
+                (gid != GID_INVALID && st.st_gid != gid);
+
+        do_chmod =
+                !S_ISLNK(st.st_mode) && /* chmod is not defined on symlinks */
+                ((mode != MODE_INVALID && ((st.st_mode ^ mode) & 07777) != 0) ||
+                 do_chown); /* If we change ownership, make sure we reset the mode afterwards, since chown()
+                             * modifies the access mode too */
+
+        if (mode == MODE_INVALID)
+                mode = st.st_mode; /* If we only shall do a chown(), save original mode, since chown() might break it. */
+        else if ((mode & S_IFMT) != 0 && ((mode ^ st.st_mode) & S_IFMT) != 0)
+                return -EINVAL; /* insist on the right file type if it was specified */
+
+        if (do_chown && do_chmod) {
+                mode_t minimal = st.st_mode & mode; /* the subset of the old and the new mask */
+
+                if (((minimal ^ st.st_mode) & 07777) != 0) {
+                        r = fchmod_opath(fd, minimal & 07777);
+                        if (r < 0) {
+                                if (!path || r != -ENOSYS)
+                                        return r;
+
+                                /* Fallback path which doesn't use /proc/self/fd/. */
+                                if (chmod(path, minimal & 07777) < 0)
+                                        return -errno;
+                        }
+                }
+        }
+
+        if (do_chown)
+                if (fchownat(fd, "", uid, gid, AT_EMPTY_PATH) < 0)
+                        return -errno;
+
+        if (do_chmod) {
+                r = fchmod_opath(fd, mode & 07777);
+                if (r < 0) {
+                        if (!path || r != -ENOSYS)
+                                return r;
+
+                        /* Fallback path which doesn't use /proc/self/fd/. */
+                        if (chmod(path, mode & 07777) < 0)
+                                return -errno;
+                }
+        }
+
+        return do_chown || do_chmod;
+}
+
+int fchmod_umask(int fd, mode_t m) {
+        _cleanup_umask_ mode_t u = umask(0777);
+
+        return RET_NERRNO(fchmod(fd, m & (~u)));
+}
+
+int fchmod_opath(int fd, mode_t m) {
+        /* This function operates also on fd that might have been opened with
+         * O_PATH. The tool set we have is non-intuitive:
+         * - fchmod(2) only operates on open files (i. e., fds with an open file description);
+         * - fchmodat(2) does not have a flag arg like fchownat(2) does, so no way to pass AT_EMPTY_PATH;
+         *   + it should not be confused with the libc fchmodat(3) interface, which adds 4th flag argument,
+         *     but does not support AT_EMPTY_PATH (only supports AT_SYMLINK_NOFOLLOW);
+         * - fchmodat2(2) supports all the AT_* flags, but is still very recent.
+         *
+         * We try to use fchmodat2(), and, if it is not supported, resort
+         * to the /proc/self/fd dance. */
+
+        assert(fd >= 0);
+
+        if (fchmodat2(fd, "", m, AT_EMPTY_PATH) >= 0)
+                return 0;
+        if (!IN_SET(errno, ENOSYS, EPERM)) /* Some container managers block unknown syscalls with EPERM */
+                return -errno;
+
+        if (chmod(FORMAT_PROC_FD_PATH(fd), m) < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                if (proc_mounted() == 0)
+                        return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
+
+                return -ENOENT;
+        }
+
+        return 0;
+}
+
+int futimens_opath(int fd, const struct timespec ts[2]) {
+        /* Similar to fchmod_opath() but for futimens() */
+
+        if (utimensat(AT_FDCWD, FORMAT_PROC_FD_PATH(fd), ts, 0) < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                if (proc_mounted() == 0)
+                        return -ENOSYS; /* if we have no /proc/, the concept is not implementable */
+
+                return -ENOENT;
+        }
+
+        return 0;
+}
+
+int stat_warn_permissions(const char *path, const struct stat *st) {
+        assert(path);
+        assert(st);
+
+        /* Don't complain if we are reading something that is not a file, for example /dev/null */
+        if (!S_ISREG(st->st_mode))
+                return 0;
+
+        if (st->st_mode & 0111)
+                log_warning("Configuration file %s is marked executable. Please remove executable permission bits. Proceeding anyway.", path);
+
+        if (st->st_mode & 0002)
+                log_warning("Configuration file %s is marked world-writable. Please remove world writability permission bits. Proceeding anyway.", path);
+
+        if (getpid_cached() == 1 && (st->st_mode & 0044) != 0044)
+                log_warning("Configuration file %s is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.", path);
+
+        return 0;
+}
+
+int fd_warn_permissions(const char *path, int fd) {
+        struct stat st;
+
+        assert(path);
+        assert(fd >= 0);
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        return stat_warn_permissions(path, &st);
+}
+
+int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode) {
+        _cleanup_close_ int fd = -EBADF;
+        int r, ret;
+
+        assert(path);
+
+        /* Note that touch_file() does not follow symlinks: if invoked on an existing symlink, then it is the symlink
+         * itself which is updated, not its target
+         *
+         * Returns the first error we encounter, but tries to apply as much as possible. */
+
+        if (parents)
+                (void) mkdir_parents(path, 0755);
+
+        /* Initially, we try to open the node with O_PATH, so that we get a reference to the node. This is useful in
+         * case the path refers to an existing device or socket node, as we can open it successfully in all cases, and
+         * won't trigger any driver magic or so. */
+        fd = open(path, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+        if (fd < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                /* if the node doesn't exist yet, we create it, but with O_EXCL, so that we only create a regular file
+                 * here, and nothing else */
+                fd = open(path, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, IN_SET(mode, 0, MODE_INVALID) ? 0644 : mode);
+                if (fd < 0)
+                        return -errno;
+        }
+
+        /* Let's make a path from the fd, and operate on that. With this logic, we can adjust the access mode,
+         * ownership and time of the file node in all cases, even if the fd refers to an O_PATH object — which is
+         * something fchown(), fchmod(), futimensat() don't allow. */
+        ret = fchmod_and_chown(fd, mode, uid, gid);
+
+        if (stamp != USEC_INFINITY) {
+                struct timespec ts[2];
+
+                timespec_store(&ts[0], stamp);
+                ts[1] = ts[0];
+                r = futimens_opath(fd, ts);
+        } else
+                r = futimens_opath(fd, NULL);
+        if (r < 0 && ret >= 0)
+                return r;
+
+        return ret;
+}
+
+int symlink_idempotent(const char *from, const char *to, bool make_relative) {
+        _cleanup_free_ char *relpath = NULL;
+        int r;
+
+        assert(from);
+        assert(to);
+
+        if (make_relative) {
+                r = path_make_relative_parent(to, from, &relpath);
+                if (r < 0)
+                        return r;
+
+                from = relpath;
+        }
+
+        if (symlink(from, to) < 0) {
+                _cleanup_free_ char *p = NULL;
+
+                if (errno != EEXIST)
+                        return -errno;
+
+                r = readlink_malloc(to, &p);
+                if (r == -EINVAL) /* Not a symlink? In that case return the original error we encountered: -EEXIST */
+                        return -EEXIST;
+                if (r < 0) /* Any other error? In that case propagate it as is */
+                        return r;
+
+                if (!streq(p, from)) /* Not the symlink we want it to be? In that case, propagate the original -EEXIST */
+                        return -EEXIST;
+        }
+
+        return 0;
+}
+
+int symlinkat_atomic_full(const char *from, int atfd, const char *to, bool make_relative) {
+        _cleanup_free_ char *relpath = NULL, *t = NULL;
+        int r;
+
+        assert(from);
+        assert(to);
+
+        if (make_relative) {
+                r = path_make_relative_parent(to, from, &relpath);
+                if (r < 0)
+                        return r;
+
+                from = relpath;
+        }
+
+        r = tempfn_random(to, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (symlinkat(from, atfd, t) < 0)
+                return -errno;
+
+        r = RET_NERRNO(renameat(atfd, t, atfd, to));
+        if (r < 0) {
+                (void) unlinkat(atfd, t, 0);
+                return r;
+        }
+
+        return 0;
+}
+
+int mknodat_atomic(int atfd, const char *path, mode_t mode, dev_t dev) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        r = tempfn_random(path, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mknodat(atfd, t, mode, dev) < 0)
+                return -errno;
+
+        r = RET_NERRNO(renameat(atfd, t, atfd, path));
+        if (r < 0) {
+                (void) unlinkat(atfd, t, 0);
+                return r;
+        }
+
+        return 0;
+}
+
+int mkfifoat_atomic(int atfd, const char *path, mode_t mode) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        /* We're only interested in the (random) filename.  */
+        r = tempfn_random(path, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mkfifoat(atfd, t, mode) < 0)
+                return -errno;
+
+        r = RET_NERRNO(renameat(atfd, t, atfd, path));
+        if (r < 0) {
+                (void) unlinkat(atfd, t, 0);
+                return r;
+        }
+
+        return 0;
+}
+
+int get_files_in_directory(const char *path, char ***list) {
+        _cleanup_strv_free_ char **l = NULL;
+        _cleanup_closedir_ DIR *d = NULL;
+        size_t n = 0;
+
+        assert(path);
+
+        /* Returns all files in a directory in *list, and the number
+         * of files as return value. If list is NULL returns only the
+         * number. */
+
+        d = opendir(path);
+        if (!d)
+                return -errno;
+
+        FOREACH_DIRENT_ALL(de, d, return -errno) {
+                if (!dirent_is_file(de))
+                        continue;
+
+                if (list) {
+                        /* one extra slot is needed for the terminating NULL */
+                        if (!GREEDY_REALLOC(l, n + 2))
+                                return -ENOMEM;
+
+                        l[n] = strdup(de->d_name);
+                        if (!l[n])
+                                return -ENOMEM;
+
+                        l[++n] = NULL;
+                } else
+                        n++;
+        }
+
+        if (list)
+                *list = TAKE_PTR(l);
+
+        return n;
+}
+
+static int getenv_tmp_dir(const char **ret_path) {
+        int r, ret = 0;
+
+        assert(ret_path);
+
+        /* We use the same order of environment variables python uses in tempfile.gettempdir():
+         * https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir */
+        FOREACH_STRING(n, "TMPDIR", "TEMP", "TMP") {
+                const char *e;
+
+                e = secure_getenv(n);
+                if (!e)
+                        continue;
+                if (!path_is_absolute(e)) {
+                        r = -ENOTDIR;
+                        goto next;
+                }
+                if (!path_is_normalized(e)) {
+                        r = -EPERM;
+                        goto next;
+                }
+
+                r = is_dir(e, true);
+                if (r < 0)
+                        goto next;
+                if (r == 0) {
+                        r = -ENOTDIR;
+                        goto next;
+                }
+
+                *ret_path = e;
+                return 1;
+
+        next:
+                /* Remember first error, to make this more debuggable */
+                if (ret >= 0)
+                        ret = r;
+        }
+
+        if (ret < 0)
+                return ret;
+
+        *ret_path = NULL;
+        return ret;
+}
+
+static int tmp_dir_internal(const char *def, const char **ret) {
+        const char *e;
+        int r, k;
+
+        assert(def);
+        assert(ret);
+
+        r = getenv_tmp_dir(&e);
+        if (r > 0) {
+                *ret = e;
+                return 0;
+        }
+
+        k = is_dir(def, true);
+        if (k == 0)
+                k = -ENOTDIR;
+        if (k < 0)
+                return r < 0 ? r : k;
+
+        *ret = def;
+        return 0;
+}
+
+int var_tmp_dir(const char **ret) {
+
+        /* Returns the location for "larger" temporary files, that is backed by physical storage if available, and thus
+         * even might survive a boot: /var/tmp. If $TMPDIR (or related environment variables) are set, its value is
+         * returned preferably however. Note that both this function and tmp_dir() below are affected by $TMPDIR,
+         * making it a variable that overrides all temporary file storage locations. */
+
+        return tmp_dir_internal("/var/tmp", ret);
+}
+
+int tmp_dir(const char **ret) {
+
+        /* Similar to var_tmp_dir() above, but returns the location for "smaller" temporary files, which is usually
+         * backed by an in-memory file system: /tmp. */
+
+        return tmp_dir_internal("/tmp", ret);
+}
+
+int unlink_or_warn(const char *filename) {
+        if (unlink(filename) < 0 && errno != ENOENT)
+                /* If the file doesn't exist and the fs simply was read-only (in which
+                 * case unlink() returns EROFS even if the file doesn't exist), don't
+                 * complain */
+                if (errno != EROFS || access(filename, F_OK) >= 0)
+                        return log_error_errno(errno, "Failed to remove \"%s\": %m", filename);
+
+        return 0;
+}
+
+int access_fd(int fd, int mode) {
+        /* Like access() but operates on an already open fd */
+
+        if (access(FORMAT_PROC_FD_PATH(fd), mode) < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                /* ENOENT can mean two things: that the fd does not exist or that /proc is not mounted. Let's
+                 * make things debuggable and distinguish the two. */
+
+                if (proc_mounted() == 0)
+                        return -ENOSYS;  /* /proc is not available or not set up properly, we're most likely in some chroot
+                                          * environment. */
+
+                return -EBADF; /* The directory exists, hence it's the fd that doesn't. */
+        }
+
+        return 0;
+}
+
+void unlink_tempfilep(char (*p)[]) {
+        /* If the file is created with mkstemp(), it will (almost always)
+         * change the suffix. Treat this as a sign that the file was
+         * successfully created. We ignore both the rare case where the
+         * original suffix is used and unlink failures. */
+        if (!endswith(*p, ".XXXXXX"))
+                (void) unlink(*p);
+}
+
+int unlinkat_deallocate(int fd, const char *name, UnlinkDeallocateFlags flags) {
+        _cleanup_close_ int truncate_fd = -EBADF;
+        struct stat st;
+        off_t l, bs;
+
+        assert((flags & ~(UNLINK_REMOVEDIR|UNLINK_ERASE)) == 0);
+
+        /* Operates like unlinkat() but also deallocates the file contents if it is a regular file and there's no other
+         * link to it. This is useful to ensure that other processes that might have the file open for reading won't be
+         * able to keep the data pinned on disk forever. This call is particular useful whenever we execute clean-up
+         * jobs ("vacuuming"), where we want to make sure the data is really gone and the disk space released and
+         * returned to the free pool.
+         *
+         * Deallocation is preferably done by FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE (👊) if supported, which means
+         * the file won't change size. That's a good thing since we shouldn't needlessly trigger SIGBUS in other
+         * programs that have mmap()ed the file. (The assumption here is that changing file contents to all zeroes
+         * underneath those programs is the better choice than simply triggering SIGBUS in them which truncation does.)
+         * However if hole punching is not implemented in the kernel or file system we'll fall back to normal file
+         * truncation (🔪), as our goal of deallocating the data space trumps our goal of being nice to readers (💐).
+         *
+         * Note that we attempt deallocation, but failure to succeed with that is not considered fatal, as long as the
+         * primary job – to delete the file – is accomplished. */
+
+        if (!FLAGS_SET(flags, UNLINK_REMOVEDIR)) {
+                truncate_fd = openat(fd, name, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW|O_NONBLOCK);
+                if (truncate_fd < 0) {
+
+                        /* If this failed because the file doesn't exist propagate the error right-away. Also,
+                         * AT_REMOVEDIR wasn't set, and we tried to open the file for writing, which means EISDIR is
+                         * returned when this is a directory but we are not supposed to delete those, hence propagate
+                         * the error right-away too. */
+                        if (IN_SET(errno, ENOENT, EISDIR))
+                                return -errno;
+
+                        if (errno != ELOOP) /* don't complain if this is a symlink */
+                                log_debug_errno(errno, "Failed to open file '%s' for deallocation, ignoring: %m", name);
+                }
+        }
+
+        if (unlinkat(fd, name, FLAGS_SET(flags, UNLINK_REMOVEDIR) ? AT_REMOVEDIR : 0) < 0)
+                return -errno;
+
+        if (truncate_fd < 0) /* Don't have a file handle, can't do more ☹️ */
+                return 0;
+
+        if (fstat(truncate_fd, &st) < 0) {
+                log_debug_errno(errno, "Failed to stat file '%s' for deallocation, ignoring: %m", name);
+                return 0;
+        }
+
+        if (!S_ISREG(st.st_mode))
+                return 0;
+
+        if (FLAGS_SET(flags, UNLINK_ERASE) && st.st_size > 0 && st.st_nlink == 0) {
+                uint64_t left = st.st_size;
+                char buffer[64 * 1024];
+
+                /* If erasing is requested, let's overwrite the file with random data once before deleting
+                 * it. This isn't going to give you shred(1) semantics, but hopefully should be good enough
+                 * for stuff backed by tmpfs at least.
+                 *
+                 * Note that we only erase like this if the link count of the file is zero. If it is higher it
+                 * is still linked by someone else and we'll leave it to them to remove it securely
+                 * eventually! */
+
+                random_bytes(buffer, sizeof(buffer));
+
+                while (left > 0) {
+                        ssize_t n;
+
+                        n = write(truncate_fd, buffer, MIN(sizeof(buffer), left));
+                        if (n < 0) {
+                                log_debug_errno(errno, "Failed to erase data in file '%s', ignoring.", name);
+                                break;
+                        }
+
+                        assert(left >= (size_t) n);
+                        left -= n;
+                }
+
+                /* Let's refresh metadata */
+                if (fstat(truncate_fd, &st) < 0) {
+                        log_debug_errno(errno, "Failed to stat file '%s' for deallocation, ignoring: %m", name);
+                        return 0;
+                }
+        }
+
+        /* Don't dallocate if there's nothing to deallocate or if the file is linked elsewhere */
+        if (st.st_blocks == 0 || st.st_nlink > 0)
+                return 0;
+
+        /* If this is a regular file, it actually took up space on disk and there are no other links it's time to
+         * punch-hole/truncate this to release the disk space. */
+
+        bs = MAX(st.st_blksize, 512);
+        l = ROUND_UP(st.st_size, bs); /* Round up to next block size */
+
+        if (fallocate(truncate_fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, 0, l) >= 0)
+                return 0; /* Successfully punched a hole! 😊 */
+
+        /* Fall back to truncation */
+        if (ftruncate(truncate_fd, 0) < 0) {
+                log_debug_errno(errno, "Failed to truncate file to 0, ignoring: %m");
+                return 0;
+        }
+
+        return 0;
+}
+
+int open_parent_at(int dir_fd, const char *path, int flags, mode_t mode) {
+        _cleanup_free_ char *parent = NULL;
+        int r;
+
+        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(path);
+
+        r = path_extract_directory(path, &parent);
+        if (r == -EDESTADDRREQ) {
+                parent = strdup(".");
+                if (!parent)
+                        return -ENOMEM;
+        } else if (r == -EADDRNOTAVAIL) {
+                parent = strdup(path);
+                if (!parent)
+                        return -ENOMEM;
+        } else if (r < 0)
+                return r;
+
+        /* Let's insist on O_DIRECTORY since the parent of a file or directory is a directory. Except if we open an
+         * O_TMPFILE file, because in that case we are actually create a regular file below the parent directory. */
+
+        if (FLAGS_SET(flags, O_PATH))
+                flags |= O_DIRECTORY;
+        else if (!FLAGS_SET(flags, O_TMPFILE))
+                flags |= O_DIRECTORY|O_RDONLY;
+
+        return RET_NERRNO(openat(dir_fd, parent, flags, mode));
+}
+
+int conservative_renameat(
+                int olddirfd, const char *oldpath,
+                int newdirfd, const char *newpath) {
+
+        _cleanup_close_ int old_fd = -EBADF, new_fd = -EBADF;
+        struct stat old_stat, new_stat;
+
+        /* Renames the old path to the new path, much like renameat() — except if both are regular files and
+         * have the exact same contents and basic file attributes already. In that case remove the new file
+         * instead. This call is useful for reducing inotify wakeups on files that are updated but don't
+         * actually change. This function is written in a style that we rather rename too often than suppress
+         * too much. I.e. whenever we are in doubt, we rather rename than fail. After all reducing inotify
+         * events is an optimization only, not more. */
+
+        old_fd = openat(olddirfd, oldpath, O_CLOEXEC|O_RDONLY|O_NOCTTY|O_NOFOLLOW);
+        if (old_fd < 0)
+                goto do_rename;
+
+        new_fd = openat(newdirfd, newpath, O_CLOEXEC|O_RDONLY|O_NOCTTY|O_NOFOLLOW);
+        if (new_fd < 0)
+                goto do_rename;
+
+        if (fstat(old_fd, &old_stat) < 0)
+                goto do_rename;
+
+        if (!S_ISREG(old_stat.st_mode))
+                goto do_rename;
+
+        if (fstat(new_fd, &new_stat) < 0)
+                goto do_rename;
+
+        if (stat_inode_same(&new_stat, &old_stat))
+                goto is_same;
+
+        if (old_stat.st_mode != new_stat.st_mode ||
+            old_stat.st_size != new_stat.st_size ||
+            old_stat.st_uid != new_stat.st_uid ||
+            old_stat.st_gid != new_stat.st_gid)
+                goto do_rename;
+
+        for (;;) {
+                uint8_t buf1[16*1024];
+                uint8_t buf2[sizeof(buf1)];
+                ssize_t l1, l2;
+
+                l1 = read(old_fd, buf1, sizeof(buf1));
+                if (l1 < 0)
+                        goto do_rename;
+
+                if (l1 == sizeof(buf1))
+                        /* Read the full block, hence read a full block in the other file too */
+
+                        l2 = read(new_fd, buf2, l1);
+                else {
+                        assert((size_t) l1 < sizeof(buf1));
+
+                        /* Short read. This hence was the last block in the first file, and then came
+                         * EOF. Read one byte more in the second file, so that we can verify we hit EOF there
+                         * too. */
+
+                        assert((size_t) (l1 + 1) <= sizeof(buf2));
+                        l2 = read(new_fd, buf2, l1 + 1);
+                }
+                if (l2 != l1)
+                        goto do_rename;
+
+                if (memcmp(buf1, buf2, l1) != 0)
+                        goto do_rename;
+
+                if ((size_t) l1 < sizeof(buf1)) /* We hit EOF on the first file, and the second file too, hence exit
+                                                 * now. */
+                        break;
+        }
+
+is_same:
+        /* Everything matches? Then don't rename, instead remove the source file, and leave the existing
+         * destination in place */
+
+        if (unlinkat(olddirfd, oldpath, 0) < 0)
+                goto do_rename;
+
+        return 0;
+
+do_rename:
+        if (renameat(olddirfd, oldpath, newdirfd, newpath) < 0)
+                return -errno;
+
+        return 1;
+}
+
+int posix_fallocate_loop(int fd, uint64_t offset, uint64_t size) {
+        RateLimit rl;
+        int r;
+
+        r = posix_fallocate(fd, offset, size); /* returns positive errnos on error */
+        if (r != EINTR)
+                return -r; /* Let's return negative errnos, like common in our codebase */
+
+        /* On EINTR try a couple of times more, but protect against busy looping
+         * (not more than 16 times per 10s) */
+        rl = (const RateLimit) { 10 * USEC_PER_SEC, 16 };
+        while (ratelimit_below(&rl)) {
+                r = posix_fallocate(fd, offset, size);
+                if (r != EINTR)
+                        return -r;
+        }
+
+        return -EINTR;
+}
+
+int parse_cifs_service(
+                const char *s,
+                char **ret_host,
+                char **ret_service,
+                char **ret_path) {
+
+        _cleanup_free_ char *h = NULL, *ss = NULL, *x = NULL;
+        const char *p, *e, *d;
+        char delimiter;
+
+        /* Parses a CIFS service in form of //host/service/path… and splitting it in three parts. The last
+         * part is optional, in which case NULL is returned there. To maximize compatibility syntax with
+         * backslashes instead of slashes is accepted too. */
+
+        if (!s)
+                return -EINVAL;
+
+        p = startswith(s, "//");
+        if (!p) {
+                p = startswith(s, "\\\\");
+                if (!p)
+                        return -EINVAL;
+        }
+
+        delimiter = s[0];
+        e = strchr(p, delimiter);
+        if (!e)
+                return -EINVAL;
+
+        h = strndup(p, e - p);
+        if (!h)
+                return -ENOMEM;
+
+        if (!hostname_is_valid(h, 0))
+                return -EINVAL;
+
+        e++;
+
+        d = strchrnul(e, delimiter);
+
+        ss = strndup(e, d - e);
+        if (!ss)
+                return -ENOMEM;
+
+        if (!filename_is_valid(ss))
+                return -EINVAL;
+
+        if (!isempty(d)) {
+                x = strdup(skip_leading_chars(d, CHAR_TO_STR(delimiter)));
+                if (!x)
+                        return -EINVAL;
+
+                /* Make sure to convert Windows-style "\" → Unix-style / */
+                for (char *i = x; *i; i++)
+                        if (*i == delimiter)
+                                *i = '/';
+
+                if (!path_is_valid(x))
+                        return -EINVAL;
+
+                path_simplify(x);
+                if (!path_is_normalized(x))
+                        return -EINVAL;
+        }
+
+        if (ret_host)
+                *ret_host = TAKE_PTR(h);
+        if (ret_service)
+                *ret_service = TAKE_PTR(ss);
+        if (ret_path)
+                *ret_path = TAKE_PTR(x);
+
+        return 0;
+}
+
+int open_mkdir_at(int dirfd, const char *path, int flags, mode_t mode) {
+        _cleanup_close_ int fd = -EBADF, parent_fd = -EBADF;
+        _cleanup_free_ char *fname = NULL, *parent = NULL;
+        int r;
+
+        /* Creates a directory with mkdirat() and then opens it, in the "most atomic" fashion we can
+         * do. Guarantees that the returned fd refers to a directory. If O_EXCL is specified will fail if the
+         * dir already exists. Otherwise will open an existing dir, but only if it is one.  */
+
+        if (flags & ~(O_RDONLY|O_CLOEXEC|O_DIRECTORY|O_EXCL|O_NOATIME|O_NOFOLLOW|O_PATH))
+                return -EINVAL;
+        if ((flags & O_ACCMODE) != O_RDONLY)
+                return -EINVAL;
+
+        /* Note that O_DIRECTORY|O_NOFOLLOW is implied, but we allow specifying it anyway. The following
+         * flags actually make sense to specify: O_CLOEXEC, O_EXCL, O_NOATIME, O_PATH */
+
+        /* If this is not a valid filename, it's a path. Let's open the parent directory then, so
+         * that we can pin it, and operate below it. */
+        r = path_extract_directory(path, &parent);
+        if (r < 0) {
+                if (!IN_SET(r, -EDESTADDRREQ, -EADDRNOTAVAIL))
+                        return r;
+        } else {
+                r = path_extract_filename(path, &fname);
+                if (r < 0)
+                        return r;
+
+                parent_fd = openat(dirfd, parent, O_PATH|O_DIRECTORY|O_CLOEXEC);
+                if (parent_fd < 0)
+                        return -errno;
+
+                dirfd = parent_fd;
+                path = fname;
+        }
+
+        fd = xopenat(dirfd, path, flags|O_CREAT|O_DIRECTORY|O_NOFOLLOW, /* xopen_flags = */ 0, mode);
+        if (IN_SET(fd, -ELOOP, -ENOTDIR))
+                return -EEXIST;
+        if (fd < 0)
+                return fd;
+
+        return TAKE_FD(fd);
+}
+
+int openat_report_new(int dirfd, const char *pathname, int flags, mode_t mode, bool *ret_newly_created) {
+        unsigned attempts = 7;
+        int fd;
+
+        /* Just like openat(), but adds one thing: optionally returns whether we created the file anew or if
+         * it already existed before. This is only relevant if O_CREAT is set without O_EXCL, and thus will
+         * shortcut to openat() otherwise */
+
+        if (!ret_newly_created)
+                return RET_NERRNO(openat(dirfd, pathname, flags, mode));
+
+        if (!FLAGS_SET(flags, O_CREAT) || FLAGS_SET(flags, O_EXCL)) {
+                fd = openat(dirfd, pathname, flags, mode);
+                if (fd < 0)
+                        return -errno;
+
+                *ret_newly_created = FLAGS_SET(flags, O_CREAT);
+                return fd;
+        }
+
+        for (;;) {
+                /* First, attempt to open without O_CREAT/O_EXCL, i.e. open existing file */
+                fd = openat(dirfd, pathname, flags & ~(O_CREAT | O_EXCL), mode);
+                if (fd >= 0) {
+                        *ret_newly_created = false;
+                        return fd;
+                }
+                if (errno != ENOENT)
+                        return -errno;
+
+                /* So the file didn't exist yet, hence create it with O_CREAT/O_EXCL. */
+                fd = openat(dirfd, pathname, flags | O_CREAT | O_EXCL, mode);
+                if (fd >= 0) {
+                        *ret_newly_created = true;
+                        return fd;
+                }
+                if (errno != EEXIST)
+                        return -errno;
+
+                /* Hmm, so now we got EEXIST? So it apparently exists now? If so, let's try to open again
+                 * without the two flags. But let's not spin forever, hence put a limit on things */
+
+                if (--attempts == 0) /* Give up eventually, somebody is playing with us */
+                        return -EEXIST;
+        }
+}
+
+int xopenat(int dir_fd, const char *path, int open_flags, XOpenFlags xopen_flags, mode_t mode) {
+        _cleanup_close_ int fd = -EBADF;
+        bool made = false;
+        int r;
+
+        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+
+        /* This is like openat(), but has a few tricks up its sleeves, extending behaviour:
+         *
+         *   • O_DIRECTORY|O_CREAT is supported, which causes a directory to be created, and immediately
+         *     opened. When used with the XO_SUBVOLUME flag this will even create a btrfs subvolume.
+         *
+         *   • If O_CREAT is used with XO_LABEL, any created file will be immediately relabelled.
+         *
+         *   • If the path is specified NULL or empty, behaves like fd_reopen().
+         */
+
+        if (isempty(path)) {
+                assert(!FLAGS_SET(open_flags, O_CREAT|O_EXCL));
+                return fd_reopen(dir_fd, open_flags & ~O_NOFOLLOW);
+        }
+
+        if (FLAGS_SET(open_flags, O_CREAT) && FLAGS_SET(xopen_flags, XO_LABEL)) {
+                r = label_ops_pre(dir_fd, path, FLAGS_SET(open_flags, O_DIRECTORY) ? S_IFDIR : S_IFREG);
+                if (r < 0)
+                        return r;
+        }
+
+        if (FLAGS_SET(open_flags, O_DIRECTORY|O_CREAT)) {
+                if (FLAGS_SET(xopen_flags, XO_SUBVOLUME))
+                        r = btrfs_subvol_make_fallback(dir_fd, path, mode);
+                else
+                        r = RET_NERRNO(mkdirat(dir_fd, path, mode));
+                if (r == -EEXIST) {
+                        if (FLAGS_SET(open_flags, O_EXCL))
+                                return -EEXIST;
+
+                        made = false;
+                } else if (r < 0)
+                        return r;
+                else
+                        made = true;
+
+                if (FLAGS_SET(xopen_flags, XO_LABEL)) {
+                        r = label_ops_post(dir_fd, path);
+                        if (r < 0)
+                                return r;
+                }
+
+                open_flags &= ~(O_EXCL|O_CREAT);
+                xopen_flags &= ~XO_LABEL;
+        }
+
+        fd = RET_NERRNO(openat(dir_fd, path, open_flags, mode));
+        if (fd < 0) {
+                if (IN_SET(fd,
+                           /* We got ENOENT? then someone else immediately removed it after we
+                           * created it. In that case let's return immediately without unlinking
+                           * anything, because there simply isn't anything to unlink anymore. */
+                           -ENOENT,
+                           /* is a symlink? exists already → created by someone else, don't unlink */
+                           -ELOOP,
+                           /* not a directory? exists already → created by someone else, don't unlink */
+                           -ENOTDIR))
+                        return fd;
+
+                if (made)
+                        (void) unlinkat(dir_fd, path, AT_REMOVEDIR);
+
+                return fd;
+        }
+
+        if (FLAGS_SET(open_flags, O_CREAT) && FLAGS_SET(xopen_flags, XO_LABEL)) {
+                r = label_ops_post(dir_fd, path);
+                if (r < 0)
+                        return r;
+        }
+
+        return TAKE_FD(fd);
+}
+
+int xopenat_lock(
+                int dir_fd,
+                const char *path,
+                int open_flags,
+                XOpenFlags xopen_flags,
+                mode_t mode,
+                LockType locktype,
+                int operation) {
+
+        _cleanup_close_ int fd = -EBADF;
+        int r;
+
+        assert(dir_fd >= 0 || dir_fd == AT_FDCWD);
+        assert(IN_SET(operation & ~LOCK_NB, LOCK_EX, LOCK_SH));
+
+        /* POSIX/UNPOSIX locks don't work on directories (errno is set to -EBADF so let's return early with
+         * the same error here). */
+        if (FLAGS_SET(open_flags, O_DIRECTORY) && !IN_SET(locktype, LOCK_BSD, LOCK_NONE))
+                return -EBADF;
+
+        for (;;) {
+                struct stat st;
+
+                fd = xopenat(dir_fd, path, open_flags, xopen_flags, mode);
+                if (fd < 0)
+                        return fd;
+
+                r = lock_generic(fd, locktype, operation);
+                if (r < 0)
+                        return r;
+
+                /* If we acquired the lock, let's check if the file/directory still exists in the file
+                 * system. If not, then the previous exclusive owner removed it and then closed it. In such a
+                 * case our acquired lock is worthless, hence try again. */
+
+                if (fstat(fd, &st) < 0)
+                        return -errno;
+                if (st.st_nlink > 0)
+                        break;
+
+                fd = safe_close(fd);
+        }
+
+        return TAKE_FD(fd);
+}