tree-wide: fix spelling of "fallback"

Similarly to "setup" vs. "set up", "fallback" is a noun, and "fall back"
is the verb. (This is pretty clear when we construct a sentence in the
present continous: "we are falling back" not "we are fallbacking").

TODO

@@ -541,7 +541,7 @@ Features:
   directory trees from the host to the services RootImage= and RootDirectory=
   environment. Which we can use for /etc/machine-id and in particular
   /etc/resolv.conf. Should be smart and do something useful on read-only
-  images, for example fallback to read-only bind mounting the file instead.
+  images, for example fall back to read-only bind mounting the file instead.
 
 * show invocation ID in systemd-run output
 
@@ -1018,7 +1018,7 @@ Features:
   - journald: also get thread ID from client, plus thread name
   - journal: when waiting for journal additions in the client always sleep at least 1s or so, in order to minimize wakeups
   - add API to close/reopen/get fd for journal client fd in libsystemd-journal.
-  - fallback to /dev/log based logging in libsystemd-journal, if we cannot log natively?
+  - fall back to /dev/log based logging in libsystemd-journal, if we cannot log natively?
   - declare the local journal protocol stable in the wiki interface chart
   - sd-journal: speed up sd_journal_get_data() with transparent hash table in bg
   - journald: when dropping msgs due to ratelimit make sure to write

meson.build

@@ -791,7 +791,7 @@ tty_gid = get_option('tty-gid')
 conf.set('TTY_GID', tty_gid)
 substs.set('TTY_GID', tty_gid)
 
-# Ensure provided GID argument is numeric, otherwise fallback to default assignment
+# Ensure provided GID argument is numeric, otherwise fall back to default assignment
 users_gid = get_option('users-gid')
 substs.set('USERS_GID', users_gid < 0 ? '-' : users_gid)
 

src/basic/fd-util.c

@@ -976,6 +976,6 @@ int read_nr_open(void) {
                         return v;
         }
 
-        /* If we fail, fallback to the hard-coded kernel limit of 1024 * 1024. */
+        /* If we fail, fall back to the hard-coded kernel limit of 1024 * 1024. */
         return 1024 * 1024;
 }

src/basic/fs-util.c

@@ -120,7 +120,7 @@ int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char
         if (!IN_SET(errno, EINVAL, ENOSYS, ENOTTY, EPERM)) /* FAT returns EPERM on link()… */
                 return -errno;
 
-        /* OK, neither RENAME_NOREPLACE nor linkat()+unlinkat() worked. Let's then fallback to the racy TOCTOU
+        /* 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)

src/basic/mountpoint-util.c

@@ -173,7 +173,7 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
                 if (!ERRNO_IS_NOT_SUPPORTED(errno) && !ERRNO_IS_PRIVILEGE(errno))
                         return -errno;
 
-                /* If statx() is not available or forbidden, fallback to name_to_handle_at() below */
+                /* If statx() is not available or forbidden, fall back to name_to_handle_at() below */
         } else if (FLAGS_SET(sx.stx_attributes_mask, STATX_ATTR_MOUNT_ROOT)) /* yay! */
                 return FLAGS_SET(sx.stx_attributes, STATX_ATTR_MOUNT_ROOT);
 
@@ -186,7 +186,7 @@ int fd_is_mount_point(int fd, const char *filename, int flags) {
                 goto fallback_fdinfo;
         else if (r == -EOPNOTSUPP)
                 /* This kernel or file system does not support name_to_handle_at(), hence let's see if the upper fs
-                 * supports it (in which case it is a mount point), otherwise fallback to the traditional stat()
+                 * supports it (in which case it is a mount point), otherwise fall back to the traditional stat()
                  * logic */
                 nosupp = true;
         else if (r < 0)

src/core/manager.c

@@ -4371,11 +4371,11 @@ const char *manager_get_confirm_spawn(Manager *m) {
          *
          * If the console suddenly disappear at the time our children will really it
          * then they will simply fail to acquire it and a positive answer will be
-         * assumed. New children will fallback to /dev/console though.
+         * assumed. New children will fall back to /dev/console though.
          *
          * Note: TTYs are devices that can come and go any time, and frequently aren't
          * available yet during early boot (consider a USB rs232 dongle...). If for any
-         * reason the configured console is not ready, we fallback to the default
+         * reason the configured console is not ready, we fall back to the default
          * console. */
 
         if (!m->confirm_spawn || path_equal(m->confirm_spawn, "/dev/console"))

src/core/namespace.c

@@ -648,7 +648,7 @@ static int clone_device_node(
                 *make_devnode = false;
         }
 
-        /* We're about to fallback to bind-mounting the device
+        /* We're about to fall back to bind-mounting the device
          * node. So create a dummy bind-mount target.
          * Do not prepare device-node SELinux label (see issue 13762) */
         r = mknod(dn, S_IFREG, 0);

src/core/service.c

@@ -1034,7 +1034,7 @@ static void service_search_main_pid(Service *s) {
 
         assert(s);
 
-        /* If we know it anyway, don't ever fallback to unreliable
+        /* If we know it anyway, don't ever fall back to unreliable
          * heuristics */
         if (s->main_pid_known)
                 return;

src/kernel-install/90-loaderentry.install

@@ -95,7 +95,7 @@ for initrd in "${INITRD_OPTIONS[@]}"; do
     fi
 done
 
-# If no initrd option is supplied, fallback to "initrd" which is
+# If no initrd option is supplied, fall back to "initrd" which is
 # the name used by dracut when generating it in its kernel-install hook
 [[ ${#INITRD_OPTIONS[@]} == 0 ]] && INITRD_OPTIONS=( initrd )
 

src/login/user-runtime-dir.c

@@ -166,7 +166,7 @@ static int do_umount(const char *user) {
         int r;
 
         /* The user may be already removed. So, first try to parse the string by parse_uid(),
-         * and if it fails, fallback to get_user_creds().*/
+         * and if it fails, fall back to get_user_creds().*/
         if (parse_uid(user, &uid) < 0) {
                 r = get_user_creds(&user, &uid, NULL, NULL, NULL, 0);
                 if (r < 0)

src/shared/dev-setup.c

@@ -72,10 +72,11 @@ int make_inaccessible_nodes(
                 { "inaccessible/sock", S_IFSOCK | 0000 },
 
                 /* The following two are likely to fail if we lack the privs for it (for example in an userns
-                 * environment, if CAP_SYS_MKNOD is missing, or if a device node policy prohibit major/minor of 0
-                 * device nodes to be created). But that's entirely fine. Consumers of these files should carry
-                 * fallback to use a different node then, for example <root>/inaccessible/sock, which is close
-                 * enough in behaviour and semantics for most uses. */
+                 * environment, if CAP_SYS_MKNOD is missing, or if a device node policy prohibits creation of
+                 * device nodes with a major/minor of 0). But that's entirely fine. Consumers of these files
+                 * should implement falling back to use a different node then, for example
+                 * <root>/inaccessible/sock, which is close enough in behaviour and semantics for most uses.
+                 */
                 { "inaccessible/chr",  S_IFCHR  | 0000 },
                 { "inaccessible/blk",  S_IFBLK  | 0000 },
         };

src/shared/dissect-image.c

@@ -813,8 +813,8 @@ int dissect_image(
                         _cleanup_free_ char *o = NULL;
                         const char *options = NULL;
 
-                        /* If the root has was set, then we won't fallback to a generic node, because the root hash
-                         * decides */
+                        /* If the root hash was set, then we won't fall back to a generic node, because the
+                         * root hash decides. */
                         if (root_hash)
                                 return -EADDRNOTAVAIL;
 
@@ -1426,7 +1426,7 @@ static int verity_partition(
                         r = crypt_activate_by_volume_key(cd, name, root_hash, root_hash_size, CRYPT_ACTIVATE_READONLY);
                 /* libdevmapper can return EINVAL when the device is already in the activation stage.
                  * There's no way to distinguish this situation from a genuine error due to invalid
-                 * parameters, so immediately fallback to activating the device with a unique name.
+                 * parameters, so immediately fall back to activating the device with a unique name.
                  * Improvements in libcrypsetup can ensure this never happens: https://gitlab.com/cryptsetup/cryptsetup/-/merge_requests/96 */
                 if (r == -EINVAL && FLAGS_SET(flags, DISSECT_IMAGE_VERITY_SHARE))
                         return verity_partition(m, v, root_hash, root_hash_size, verity_data, NULL, root_hash_sig ?: hash_sig_from_file, root_hash_sig_size, flags & ~DISSECT_IMAGE_VERITY_SHARE, d);

src/shared/reboot-util.h

@@ -6,7 +6,7 @@ int update_reboot_parameter_and_warn(const char *parameter, bool keep);
 typedef enum RebootFlags {
         REBOOT_LOG      = 1 << 0, /* log about what we are going to do and all errors */
         REBOOT_DRY_RUN  = 1 << 1, /* return 0 right before actually doing the reboot */
-        REBOOT_FALLBACK = 1 << 2, /* fallback to plain reboot() if argument-based reboot doesn't work, isn't configured or doesn't apply otherwise */
+        REBOOT_FALLBACK = 1 << 2, /* fall back to plain reboot() if argument-based reboot doesn't work, isn't configured or doesn't apply otherwise */
 } RebootFlags;
 
 int read_reboot_parameter(char **parameter);

src/shared/resolve-util.h

@@ -53,7 +53,7 @@ enum DnsOverTlsMode {
         DNS_OVER_TLS_NO,
 
         /* Try to connect using DNS-over-TLS, but if connection fails,
-         * fallback to using an unencrypted connection */
+         * fall back to using an unencrypted connection */
         DNS_OVER_TLS_OPPORTUNISTIC,
 
         /* Enforce DNS-over-TLS and require valid server certificates */

src/udev/udev-builtin-usb_id.c

@@ -372,7 +372,7 @@ fallback:
         if (r < 0)
                 return log_device_debug_errno(dev_usb, r, "Failed to get idProduct attribute: %m");
 
-        /* fallback to USB vendor & device */
+        /* fall back to USB vendor & device */
         if (vendor_str[0] == '\0') {
                 const char *usb_vendor;