devices: --devices/--specials/-D/--copy-devices/--write-devices

Recreate char/block nodes via mknodat (privilege-gated, EPERM->warn+skip) and
FIFOs via mkfifoat; new STATUS_SPECIAL frame + validated rdev; sockets skipped;
-copy-devices copies st_size; -write-devices O_NOFOLLOW+O_NONBLOCK warn+skip.
preserve_specials/copy_devices/write_devices cross the wire. PROTOCOL_VERSION
2.12.0->2.13.0. Review fixes: -m source-removal keeps recreated specials, FIFO
ENXIO skip, rdev bounds at chunk_deserialize, STATUS_ERROR on receive branch,
scanner_prepare_special dedup.

src/client/client_cli.c

@@ -537,6 +537,11 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--numeric-ids", NULL, OPT_FLAG, offsetof(Config, numeric_ids)},
     {"--atimes", "-U", OPT_FLAG, offsetof(Config, preserve_atimes)},
     {"--crtimes", "-N", OPT_FLAG, offsetof(Config, preserve_crtimes)},
+    /* -D is handled separately (it implies both --devices and --specials). */
+    {"--devices", NULL, OPT_FLAG, offsetof(Config, preserve_devices)},
+    {"--specials", NULL, OPT_FLAG, offsetof(Config, preserve_specials)},
+    {"--copy-devices", NULL, OPT_FLAG, offsetof(Config, copy_devices)},
+    {"--write-devices", NULL, OPT_FLAG, offsetof(Config, write_devices)},
     {"--omit-dir-times", "-O", OPT_FLAG, offsetof(Config, omit_dir_times)},
     {"--omit-link-times", "-J", OPT_FLAG, offsetof(Config, omit_link_times)},
     {"--open-noatime", NULL, OPT_FLAG, offsetof(Config, open_noatime)},
@@ -831,6 +836,12 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
     } else if (opt_is(argv[i], "-V", "--version")) {
       printf("fastsync version %s\n", PROTOCOL_VERSION);
       return 1;
+    } else if (opt_is(argv[i], "-D", NULL)) {
+      /* rsync -D == --devices --specials.  -D is otherwise unassigned in
+         FastSync (verified: no collision), so it is free to imply both. */
+      config->preserve_devices = true;
+      config->preserve_specials = true;
+      log_info_message(LOG_INFO_MISC, "Enabled preservation of device and special files (-D)");
     } else if (opt_is(argv[i], "-a", "--archive")) {
       config->use_compression =
           !config->compress_choice || strcmp(config->compress_choice, "zstd") == 0;
@@ -1200,6 +1211,15 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
     config->files_from_set = set;
   }
 
+  /* Device/special preservation recreates a node from its metadata mode (whose
+     S_IFMT bits carry the node kind), so --devices/--specials/-D imply metadata
+     transmission.  --copy-devices/--write-devices treat the entry as data but a
+     mtime/mode-preserving transfer still benefits from metadata, so all four
+     imply it (FastSync's broad -M bundle; ownership stays opt-in). */
+  if (config->preserve_devices || config->preserve_specials || config->copy_devices ||
+      config->write_devices)
+    config->use_metadata = true;
+
   /* The "unchanged" decision for --compare-dest/--copy-dest/--link-dest must
    * be made on the receiver against the basis directories, which requires the
    * per-file STATUS_CHECK handshake: basis-dir options therefore imply

src/client/client_send.c

@@ -104,6 +104,9 @@ static bool prepare_scanner(const Config* config, int num_threads, PreparedScann
   options->copy_unsafe_links = config->copy_unsafe_links;
   options->checksum = config->checksum;
   options->one_file_system = config->one_file_system;
+  options->preserve_devices = config->preserve_devices;
+  options->preserve_specials = config->preserve_specials;
+  options->copy_devices = config->copy_devices;
   options->file_list = (const FileListSet*)config->files_from_set;
   options->base_filters = out->base_filters;
   options->per_dir_filters = config->per_dir_filter;
@@ -1248,6 +1251,14 @@ static int send_chunk_with_removal(Client* client, Chunk* chunk, Config* config,
       change_emit_file_sent(config, f);
       continue;
     }
+    /* --devices/--specials: a device/special node is recreated on the receiver,
+       not transferred as content.  Send the dedicated STATUS_SPECIAL frame. */
+    if (f->is_special) {
+      if (!file_send_special(f, client->file_descriptor, config->use_metadata))
+        return -1;
+      change_emit_file_sent(config, f);
+      continue;
+    }
     bool stream = f->data->data == NULL && f->data->size > 0;
     bool use_sendfile =
         (config->use_sendfile && !config->use_compression) || (stream && !config->use_compression);

src/client/scanner.c

@@ -10,6 +10,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <sys/sysmacros.h>
 #include <threads.h>
 #include <unistd.h>
 #include <limits.h>
@@ -193,6 +194,34 @@ static void scanner_assign_hardlink(DirectoryScanner* scanner, HardLinkTable* ta
   }
 }
 
+/* Phase 4 special/devices: detect a device (char/block), FIFO or socket entry
+   and, when the matching --devices/--specials flag asks it be preserved,
+   convert the File into a node to recreate (is_special, empty payload) with its
+   device rdev captured from the source stat.  When the entry is not preserved
+   (or --copy-devices instead copies its content as an ordinary regular file)
+   the File is left as a normal data file.  Returns true when converted. */
+static bool scanner_prepare_special(bool preserve_devices, bool preserve_specials, File* file,
+                                    const struct stat* stats) {
+  if (!file || !stats)
+    return false;
+  bool is_device = S_ISCHR(stats->st_mode) || S_ISBLK(stats->st_mode);
+  bool is_fifo = S_ISFIFO(stats->st_mode);
+  bool is_socket = S_ISSOCK(stats->st_mode);
+  if (!is_device && !is_fifo && !is_socket)
+    return false;
+  bool preserve = is_device ? preserve_devices : preserve_specials;
+  if (!preserve)
+    return false;
+  file->is_special = true;
+  file->data->size = 0;
+  file->data->data = NULL;
+  if (is_device) {
+    file->rdev_major = (int32_t)major(stats->st_rdev);
+    file->rdev_minor = (int32_t)minor(stats->st_rdev);
+  }
+  return true;
+}
+
 /* Append `rel` to the caller's exclusion sink, taking `mtx` when shared across
    parallel worker threads.  Returns false on allocation failure (list left
    unchanged). */
@@ -365,6 +394,9 @@ DirectoryScanner* directory_scanner_create_with_options(const char* root_directo
   scanner->copy_unsafe_links = options->copy_unsafe_links;
   scanner->checksum = options->checksum;
   scanner->one_file_system = options->one_file_system;
+  scanner->preserve_devices = options->preserve_devices;
+  scanner->preserve_specials = options->preserve_specials;
+  scanner->copy_devices = options->copy_devices;
   scanner->failed = false;
   scanner->root_path = str_dup(root_directory);
   if (!scanner->root_path) {
@@ -925,6 +957,9 @@ Chunk* directory_scanner_next(DirectoryScanner* scanner) {
         file->send_path = rel_copy;
         rel_copy = NULL;
       }
+      /* --devices/--specials: a device/FIFO/socket entry marked for preservation
+         becomes a node to recreate (is_special, no data, rdev captured). */
+      scanner_prepare_special(scanner->preserve_devices, scanner->preserve_specials, file, &stats);
       if (scanner->hardlinks && S_ISREG(stats.st_mode))
         scanner_assign_hardlink(scanner, scanner->hardlinks, file, &stats);
       if (scanner->use_metadata)
@@ -1243,6 +1278,7 @@ static void scan_root_entry(const ScannerOptions* options, const FilterNode* roo
     file->send_path = rel;
     rel = NULL;
   }
+  scanner_prepare_special(options->preserve_devices, options->preserve_specials, file, &st);
   if (options->hardlinks && S_ISREG(st.st_mode)) {
     int gid;
     bool is_first;

src/client/scanner.h

@@ -34,6 +34,12 @@ typedef struct {
   bool copy_unsafe_links;
   bool checksum;
   bool one_file_system;
+  /* Phase 4 special/devices: whether device nodes (--devices) and special files
+   * (--specials) are preserved via recreation, and whether --copy-devices
+   * copies a device's content as an ordinary regular file. */
+  bool preserve_devices;
+  bool preserve_specials;
+  bool copy_devices;
   /* Phase 2 (files-from / filter layer). All pointers are shared read-only
    * across scanner instances and worker threads; ownership stays with the
    * caller (client_send). */
@@ -104,6 +110,10 @@ typedef struct {
   bool one_file_system;
   dev_t root_dev;
   bool failed;
+  /* Phase 4 special/devices (see ScannerOptions). */
+  bool preserve_devices;
+  bool preserve_specials;
+  bool copy_devices;
   /* Phase 2 (files-from / filter layer). */
   char* root_path;          /* transfer root (fs path) for rel computation */
   char* current_rel;        /* rel path of the open directory ("" == root) */

src/client/usage.c

@@ -182,6 +182,15 @@ void print_usage(void) {
   printf("  --copy-unsafe-links  Only transform unsafe symlinks into referent files\n");
   printf("  -H, --hard-links    Preserve hard-link relationships across the transfer\n");
   printf("  -S, --sparse        Handle sparse files efficiently\n");
+  printf(
+      "  -D                  Preserve device and special files (implies --devices --specials)\n");
+  printf(
+      "  --devices           Recreate device nodes on the destination (privileged; skipped when\n");
+  printf("                      the receiver lacks CAP_MKNOD)\n");
+  printf("  --specials          Recreate special files (FIFOs) on the destination (sockets "
+         "skipped)\n");
+  printf("  --copy-devices      Copy a source device's content as a regular file instead\n");
+  printf("  --write-devices     Write received data into an existing destination device node\n");
   printf("  --inplace           Update files in-place (no temp+rename)\n");
   printf(
       "  --preallocate       Allocate destination file space up front (fail-fast on full disk)\n");

src/server/receiver.c

@@ -154,7 +154,8 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
   DeleteManifest* deferred_manifest = NULL;
   while (status == STATUS_NEXT || status == STATUS_CHUNK || status == STATUS_CHECK ||
          status == STATUS_KEEPALIVE || status == STATUS_ABORT || status == STATUS_CHECK_BATCH ||
-         status == STATUS_MKDIR || status == STATUS_MANIFEST || status == STATUS_HARDLINK) {
+         status == STATUS_MKDIR || status == STATUS_MANIFEST || status == STATUS_HARDLINK ||
+         status == STATUS_SPECIAL) {
     if (status == STATUS_KEEPALIVE) {
       if (!send_status(file_descriptor, STATUS_KEEPALIVE))
         goto fail;
@@ -185,6 +186,10 @@ int receiver_process_pending(Config* config, int file_descriptor, const Receiver
       File* file = file_receive_hardlink(file_descriptor);
       if (!file || !sink->store_file(file, sink->context))
         goto receive_error;
+    } else if (status == STATUS_SPECIAL) {
+      File* file = file_receive_special(file_descriptor);
+      if (!file || !sink->store_file(file, sink->context))
+        goto receive_error;
     } else if (status == STATUS_MANIFEST) {
       DeleteManifest* manifest = receive_manifest_entries(file_descriptor);
       if (!manifest)
@@ -309,7 +314,8 @@ static bool receiver_save_file(File* file, void* context_pointer) {
     result = file_save_to_disk_full(context->config->receive_root_directory, file, context->config);
   }
   if (result != FILE_SAVE_ERROR && context->config->remove_source_files && !file->is_dir &&
-      !file->skip && !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
+      !file->is_special && !file->skip &&
+      !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
     file_destroy(file);
     return false;
   }

src/shared/chunk.c

@@ -74,10 +74,17 @@ static unsigned long long per_file_serialize_size(File* file, bool use_metadata)
   if (metadata_size > ULLONG_MAX - size)
     return 0;
   size += metadata_size;
-  /* Entry type marker: 0 = regular file, 1 = explicit directory entry. */
+  /* Entry type marker: 0 = regular file, 1 = explicit directory entry,
+   * 2 = special/device node (recreated by the receiver). */
   if (sizeof(int) > ULLONG_MAX - size)
     return 0;
   size += sizeof(int);
+  /* A special node also carries its rdev major/minor. */
+  if (file->is_special) {
+    if (2 * sizeof(int32_t) > ULLONG_MAX - size)
+      return 0;
+    size += 2 * sizeof(int32_t);
+  }
   if (sizeof(size_t) > ULLONG_MAX - size)
     return 0;
   size += sizeof(size_t);
@@ -116,10 +123,19 @@ Data* chunk_serialize(Chunk* chunk, bool use_metadata) {
     memcpy(data_pointer, wire_path, path_len);
     data_pointer += path_len;
 
-    int entry_type = file->is_dir ? 1 : 0;
+    int entry_type = file->is_dir ? 1 : (file->is_special ? 2 : 0);
     memcpy(data_pointer, &entry_type, sizeof(int));
     data_pointer += sizeof(int);
 
+    if (file->is_special) {
+      int32_t special_major = file->rdev_major;
+      int32_t special_minor = file->rdev_minor;
+      memcpy(data_pointer, &special_major, sizeof(special_major));
+      data_pointer += sizeof(special_major);
+      memcpy(data_pointer, &special_minor, sizeof(special_minor));
+      data_pointer += sizeof(special_minor);
+    }
+
     if (use_metadata)
       metadata_to_buf(&data_pointer, file->metadata);
 
@@ -206,16 +222,45 @@ Chunk* chunk_deserialize(Data* data, bool use_metadata) {
     }
     int entry_type;
     memcpy(&entry_type, data_pointer, sizeof(int));
-    if (entry_type != 0 && entry_type != 1) {
+    if (entry_type != 0 && entry_type != 1 && entry_type != 2) {
       log_message(LOG_LEVEL_ERROR, "Invalid chunk format: bad entry type");
       file_destroy(file);
       array_list_delete(files);
       return NULL;
     }
     file->is_dir = entry_type == 1;
+    file->is_special = entry_type == 2;
     data_pointer += sizeof(int);
     remaining_size -= sizeof(int);
 
+    if (file->is_special) {
+      if (remaining_size < 2 * (int32_t)sizeof(int32_t)) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for special rdev");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      int32_t special_major, special_minor;
+      memcpy(&special_major, data_pointer, sizeof(special_major));
+      data_pointer += sizeof(special_major);
+      memcpy(&special_minor, data_pointer, sizeof(special_minor));
+      data_pointer += sizeof(special_minor);
+      remaining_size -= 2 * sizeof(int32_t);
+      /* Reject an out-of-range/negative rdev here as a malformed chunk (the
+         same 0xffff / 0x00ffffff bounds file_special_rdev_valid uses), so a
+         bogus large-but-positive rdev is refused cleanly instead of being
+         deferred to the creation site where it would abort after the frame. */
+      if (special_major < 0 || special_minor < 0 || special_major > 0xffff ||
+          special_minor > 0x00ffffff) {
+        log_message(LOG_LEVEL_ERROR, "Invalid chunk format: out-of-range special rdev");
+        file_destroy(file);
+        array_list_delete(files);
+        return NULL;
+      }
+      file->rdev_major = special_major;
+      file->rdev_minor = special_minor;
+    }
+
     if (use_metadata) {
       if (remaining_size < sizeof(int)) {
         log_message(LOG_LEVEL_ERROR, "Invalid chunk format: not enough data for metadata");

src/shared/config.c

@@ -76,6 +76,9 @@ static void config_set_defaults(Config* config) {
   config->preserve_xattrs = false;
   config->preserve_devices = false;
   config->preserve_sparse = false;
+  config->preserve_specials = false;
+  config->copy_devices = false;
+  config->write_devices = false;
   config->itemize_changes = false;
   config->out_format = NULL;
   config->log_file_format = NULL;
@@ -180,16 +183,18 @@ static bool validate_received_config(const Config* config) {
          valid_wire_bool(config->safe_links) && valid_wire_bool(config->copy_unsafe_links) &&
          valid_wire_bool(config->preserve_hard_links) && valid_wire_bool(config->preserve_acls) &&
          valid_wire_bool(config->preserve_xattrs) && valid_wire_bool(config->preserve_devices) &&
-         valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->ignore_existing) &&
-         valid_wire_bool(config->existing) && valid_wire_bool(config->update) &&
-         valid_wire_bool(config->inplace) && valid_wire_bool(config->append) &&
-         valid_wire_bool(config->use_fsync) && valid_wire_bool(config->append_verify) &&
-         valid_wire_bool(config->delete_excluded) && valid_wire_bool(config->force_delete) &&
-         valid_wire_bool(config->delete_missing_args) && valid_wire_bool(config->delete_after) &&
-         valid_wire_bool(config->preallocate) && valid_wire_bool(config->delete_delay) &&
-         valid_wire_bool(config->delete_during) && valid_wire_bool(config->relative) &&
-         valid_wire_bool(config->prune_empty_dirs) && valid_wire_bool(config->delay_updates) &&
-         valid_wire_bool(config->mkpath) && !(config->delay_updates && config->inplace) &&
+         valid_wire_bool(config->preserve_sparse) && valid_wire_bool(config->preserve_specials) &&
+         valid_wire_bool(config->copy_devices) && valid_wire_bool(config->write_devices) &&
+         valid_wire_bool(config->ignore_existing) && valid_wire_bool(config->existing) &&
+         valid_wire_bool(config->update) && valid_wire_bool(config->inplace) &&
+         valid_wire_bool(config->append) && valid_wire_bool(config->use_fsync) &&
+         valid_wire_bool(config->append_verify) && valid_wire_bool(config->delete_excluded) &&
+         valid_wire_bool(config->force_delete) && valid_wire_bool(config->delete_missing_args) &&
+         valid_wire_bool(config->delete_after) && valid_wire_bool(config->preallocate) &&
+         valid_wire_bool(config->delete_delay) && valid_wire_bool(config->delete_during) &&
+         valid_wire_bool(config->relative) && valid_wire_bool(config->prune_empty_dirs) &&
+         valid_wire_bool(config->delay_updates) && valid_wire_bool(config->mkpath) &&
+         !(config->delay_updates && config->inplace) &&
          !(config->delay_updates && delay_updates_staging_name_conflict(config->backup_dir)) &&
          valid_wire_bool(config->partial) && valid_wire_bool(config->delete_before) &&
          valid_wire_bool(config->checksum) && valid_wire_bool(config->eight_bit_output) &&
@@ -444,12 +449,16 @@ static bool send_delta_fields(int fd, const Config* c) {
 }
 
 static bool send_file_options(int fd, const Config* c) {
+  /* Device/special preservation flags cross the wire so the receiver knows a
+   * special/device entry must be recreated.  Trailing fields; protocol 2.13.0. */
   return send_int(fd, c->backup) && send_str(fd, c->backup_dir ? c->backup_dir : "") &&
          send_int(fd, c->remove_source_files) && send_int(fd, c->follow_symlinks) &&
          send_int(fd, c->copy_links) && send_int(fd, c->safe_links) &&
          send_int(fd, c->copy_unsafe_links) && send_int(fd, c->preserve_hard_links) &&
          send_int(fd, c->preserve_acls) && send_int(fd, c->preserve_xattrs) &&
-         send_int(fd, c->preserve_devices) && send_int(fd, c->preserve_sparse);
+         send_int(fd, c->preserve_devices) && send_int(fd, c->preserve_sparse) &&
+         send_int(fd, c->preserve_specials) && send_int(fd, c->copy_devices) &&
+         send_int(fd, c->write_devices);
 }
 
 static bool send_selection_options(int fd, const Config* c) {
@@ -569,7 +578,8 @@ static bool receive_file_options(int fd, Config* c) {
     return false;
   bool* flags[] = {&c->follow_symlinks,   &c->copy_links,          &c->safe_links,
                    &c->copy_unsafe_links, &c->preserve_hard_links, &c->preserve_acls,
-                   &c->preserve_xattrs,   &c->preserve_devices,    &c->preserve_sparse};
+                   &c->preserve_xattrs,   &c->preserve_devices,    &c->preserve_sparse,
+                   &c->preserve_specials, &c->copy_devices,        &c->write_devices};
   for (size_t i = 0; i < sizeof(flags) / sizeof(flags[0]); i++) {
     if (!receive_wire_bool(fd, flags[i]))
       return false;

src/shared/config.h

@@ -115,6 +115,22 @@ typedef struct Config {
   bool preserve_xattrs;
   bool preserve_devices;
   bool preserve_sparse;
+  /* Phase 4 special/devices: preserve special files (FIFOs, sockets) and device
+   * nodes on the destination by recreating them (mknod/mkfifo) instead of
+   * transferring content.  preserve_specials mirrors rsync --specials (the
+   * special-file half of -D); preserve_devices mirrors --devices (the device
+   * half of -D); both CROSS the wire so the receiver knows a special/device
+   * entry must be recreated rather than written as a regular file. */
+  bool preserve_specials;
+  /* --copy-devices: copy the CONTENT of a source device as an ordinary regular
+   * file on the destination (rsync's non-privileged safe mode), instead of
+   * recreating the device node.  CROSSES the wire (receiver treats the entry as
+   * a regular file, which is the default, so this is belt-and-braces). */
+  bool copy_devices;
+  /* --write-devices: write the received data directly INTO an existing device
+   * node on the destination instead of creating a regular file.  Dangeroud;
+   * see RSYNC_COMPAT.md for the tight gating.  CROSSES the wire. */
+  bool write_devices;
 
   // Issue #122: Output/logging options
   bool itemize_changes;
@@ -312,7 +328,7 @@ typedef struct Config {
   bool open_noatime;
 } Config;
 
-#define PROTOCOL_VERSION "2.12.0"
+#define PROTOCOL_VERSION "2.13.0"
 #define DEFAULT_CHUNK_SIZE (10 * 1024 * 1024)
 /* Upper bound on total basis-dir entries (rsync caps --link-dest at 20). */
 #define MAX_BASIS_DIRS 64

src/shared/file.c

@@ -114,6 +114,9 @@ File* file_create(const char* path) {
   file->link_group = 0;
   file->link_first = false;
   file->hardlink_target = NULL;
+  file->is_special = false;
+  file->rdev_major = 0;
+  file->rdev_minor = 0;
   return file;
 }
 

src/shared/file_receive.c

@@ -6,6 +6,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
+#include <sys/sysmacros.h>
 #include <unistd.h>
 
 #include "array_list.h"
@@ -288,6 +289,231 @@ static FileSaveResult file_save_hardlink_sibling(const char* root_directory, con
   return ok ? FILE_SAVE_WRITTEN : FILE_SAVE_ERROR;
 }
 
+/* Validate a transmitted special rdev against the node kind implied by `mode`'s
+ * S_IFMT bits.  Char/block devices require a legal major/minor pair (non-negative,
+ * range-checked); a non-device special (FIFO/socket) must carry an empty rdev.
+ * Used identically on the wire path and at the secure recreation site so a
+ * malicious/bogus rdev can never drive a dangerous node. */
+bool file_special_rdev_valid(int32_t major, int32_t minor, mode_t mode) {
+  bool is_device = S_ISCHR(mode) || S_ISBLK(mode);
+  if (is_device)
+    return major >= 0 && minor >= 0 && major <= 0xffff && minor <= 0x00ffffff;
+  /* A non-device entry must actually be a special (FIFO/socket) and carry no
+     rdev; a regular/dir mode is never a valid special node. */
+  return (S_ISFIFO(mode) || S_ISSOCK(mode)) && major == 0 && minor == 0;
+}
+
+/* ---- Device/special node RECREATION (--devices/--specials), receiver side ----
+ *
+ * Privilege gating: making a real device node requires CAP_MKNOD (root); making
+ * a FIFO works unprivileged (mkfifo).  When the receiver lacks the capability,
+ * mknodat() fails with EPERM and the entry is SKIPPED with a warning -- the
+ * whole transfer must NOT abort just because the environment cannot make the
+ * node.  CI runs non-root, so device creation is expected to skip there and
+ * only a FIFO is honestly assertable unprivileged.
+ *
+ * Confinement: the parent directory is opened fd-relative below the receive
+ * root (file_open_secure_parent: O_NOFOLLOW, no "..", root-checked) and the
+ * node is created with mknodat()/mkfifoat(), so it can never be placed outside
+ * the confined root and never follows a symlink.
+ *
+ * rdev validation: a malicious/bogus rdev (negative, out-of-range) is rejected
+ * here as well as on the wire (file_receive_special / chunk_deserialize), and a
+ * non-device entry must carry an empty rdev.
+ */
+static FileSaveResult file_save_special_to_disk(const char* root_directory, const File* file,
+                                                const Config* config) {
+  if (!root_directory || !file || !file->path || file->path[0] == '\0' ||
+      has_path_traversal(file->path) || !file->metadata)
+    return FILE_SAVE_ERROR;
+
+  mode_t mode = file->metadata->mode;
+  bool is_char = S_ISCHR(mode);
+  bool is_blk = S_ISBLK(mode);
+  bool is_fifo = S_ISFIFO(mode);
+  bool is_sock = S_ISSOCK(mode);
+  if (!is_char && !is_blk && !is_fifo && !is_sock) {
+    log_message(LOG_LEVEL_ERROR, "Special node has no device/FIFO/socket mode");
+    return FILE_SAVE_ERROR;
+  }
+  if (is_sock) {
+    /* No standard filesystem call recreates a socket; best-effort unsupported. */
+    log_message(LOG_LEVEL_WARNING, "socket not recreated: %s (unsupported; skipped)", file->path);
+    return FILE_SAVE_SKIPPED;
+  }
+  if (is_char || is_blk) {
+    if (!config || !config->preserve_devices)
+      return FILE_SAVE_SKIPPED;
+  } else if (is_fifo) {
+    if (!config || !config->preserve_specials)
+      return FILE_SAVE_SKIPPED;
+  }
+  /* Defense-in-depth rdev/type validation (also done on the wire path). */
+  if (!file_special_rdev_valid(file->rdev_major, file->rdev_minor, mode)) {
+    log_message(LOG_LEVEL_ERROR, "Rejected out-of-range device rdev %d:%d", file->rdev_major,
+                file->rdev_minor);
+    return FILE_SAVE_ERROR;
+  }
+
+  char* destination = path_cat(root_directory, file->path);
+  if (!destination)
+    return FILE_SAVE_ERROR;
+  char* leaf = NULL;
+  int parent_fd = file_open_secure_parent(destination, &leaf, true);
+  if (parent_fd < 0) {
+    free(destination);
+    return FILE_SAVE_ERROR;
+  }
+
+  /* --existing / --ignore-existing / --update decide against the node that
+     would be replaced, mirroring the regular-file path. */
+  if (config->existing && !file_path_exists_secure(destination)) {
+    close(parent_fd);
+    free(leaf);
+    free(destination);
+    return FILE_SAVE_SKIPPED;
+  }
+  if (config->ignore_existing && file_path_exists_secure(destination)) {
+    close(parent_fd);
+    free(leaf);
+    free(destination);
+    return FILE_SAVE_SKIPPED;
+  }
+  if (config->update && file_destination_is_newer_secure(destination, file->metadata)) {
+    close(parent_fd);
+    free(leaf);
+    free(destination);
+    return FILE_SAVE_SKIPPED;
+  }
+
+  dev_t rdev = 0;
+  mode_t create_mode;
+  if (is_char) {
+    create_mode = S_IFCHR;
+    rdev = makedev((unsigned)file->rdev_major, (unsigned)file->rdev_minor);
+  } else if (is_blk) {
+    create_mode = S_IFBLK;
+    rdev = makedev((unsigned)file->rdev_major, (unsigned)file->rdev_minor);
+  } else {
+    create_mode = S_IFIFO;
+  }
+  mode_t perms = mode & 0777;
+
+  int rc = is_fifo ? mkfifoat(parent_fd, leaf, perms)
+                   : mknodat(parent_fd, leaf, create_mode | perms, rdev);
+  if (rc != 0) {
+    if (errno == EEXIST) {
+      /* An entry already exists: only skip when it already is a matching node;
+         never replace an existing directory or unrelated entry with the node. */
+      struct stat st;
+      if (fstatat(parent_fd, leaf, &st, AT_SYMLINK_NOFOLLOW) == 0 &&
+          ((is_char && S_ISCHR(st.st_mode)) || (is_blk && S_ISBLK(st.st_mode)) ||
+           (is_fifo && S_ISFIFO(st.st_mode)))) {
+        close(parent_fd);
+        free(leaf);
+        free(destination);
+        return FILE_SAVE_SKIPPED;
+      }
+      log_message(LOG_LEVEL_WARNING, "refusing to replace existing entry with %s: %s (skipped)",
+                  is_fifo ? "FIFO" : "device", file->path);
+    } else if (errno == EPERM || errno == EACCES) {
+      /* Missing CAP_MKNOD / parent write permission: the environment cannot
+         create the node, so skip instead of failing the whole run. */
+      log_message(LOG_LEVEL_WARNING,
+                  "skipping %s: cannot create %s node (%s)\n"
+                  "  --devices/--specials node creation needs privilege (CAP_MKNOD)",
+                  file->path, is_fifo ? "FIFO" : "device", strerror(errno));
+    } else {
+      log_message(LOG_LEVEL_WARNING, "failed to create %s %s: %s (skipped)",
+                  is_fifo ? "FIFO" : "device", file->path, strerror(errno));
+    }
+    close(parent_fd);
+    free(leaf);
+    free(destination);
+    return FILE_SAVE_SKIPPED;
+  }
+
+  /* Apply mtime on the fresh node (utimensat, no-follow).  Ownership is not
+     applied -- identity fchown needs an fd and would require opening the node. */
+  struct timespec times[2] = {
+      {.tv_sec = 0, .tv_nsec = UTIME_OMIT},
+      {.tv_sec = file->metadata->mtime_sec, .tv_nsec = file->metadata->mtime_nsec}};
+  utimensat(parent_fd, leaf, times, AT_SYMLINK_NOFOLLOW);
+  close(parent_fd);
+  free(leaf);
+  free(destination);
+  return FILE_SAVE_WRITTEN;
+}
+
+/* --write-devices (receiver): write the received data directly into an EXISTING
+ * device node on the destination instead of creating a regular file.  The node
+ * must already exist and be a char/block device (the device itself is opened and
+ * followed); it is confined to the receive root via file_open_secure_parent.
+ * Dangerous by nature, so deliberately restricted: a missing/non-device
+ * destination, or a write failure, is SKIPPED with a warning rather than
+ * allowed.  On environments without device access the run still succeeds (the
+ * entry is skipped), never aborts. */
+static FileSaveResult file_save_write_device(const char* root_directory, const File* file) {
+  if (!root_directory || !file || !file->path || file->path[0] == '\0' ||
+      has_path_traversal(file->path))
+    return FILE_SAVE_ERROR;
+  if (!file->data)
+    return FILE_SAVE_ERROR;
+  char* destination = path_cat(root_directory, file->path);
+  if (!destination)
+    return FILE_SAVE_ERROR;
+  char* leaf = NULL;
+  int parent_fd = file_open_secure_parent(destination, &leaf, false);
+  if (parent_fd < 0) {
+    free(destination);
+    return FILE_SAVE_SKIPPED;
+  }
+  /* O_NONBLOCK: a pre-existing FIFO at the target would otherwise block the
+       receive thread forever on open(2).  With it the open only succeeds for a
+       readerless FIFO with O_RDWR (which the device fstat gate rejects anyway)
+       or fails with ENXIO/EAGAIN, both treated as a normal skip below. */
+  int fd = openat(parent_fd, leaf, O_WRONLY | O_CLOEXEC | O_NOFOLLOW | O_NONBLOCK);
+  int saved_errno = errno;
+  free(leaf);
+  close(parent_fd);
+  if (fd < 0) {
+    free(destination);
+    if (saved_errno == ENXIO || saved_errno == EAGAIN) {
+      /* A FIFO with no reader / an unreadable special: skip like every other
+         unusable write-devices target instead of blocking or failing. */
+      log_message(LOG_LEVEL_WARNING, "write-devices: %s not writable (%s); skipped", file->path,
+                  strerror(saved_errno));
+    } else {
+      log_message(LOG_LEVEL_WARNING, "write-devices: cannot open %s (%s); skipped", file->path,
+                  strerror(saved_errno));
+    }
+    return FILE_SAVE_SKIPPED;
+  }
+  struct stat st;
+  if (fstat(fd, &st) != 0 || !(S_ISCHR(st.st_mode) || S_ISBLK(st.st_mode))) {
+    close(fd);
+    free(destination);
+    log_message(LOG_LEVEL_WARNING, "write-devices: %s is not a device node; skipped", file->path);
+    return FILE_SAVE_SKIPPED;
+  }
+  bool ok = true;
+  if (file->data->size > 0) {
+    size_t total = (size_t)file->data->size;
+    size_t written = 0;
+    while (written < total) {
+      ssize_t n = write(fd, (char*)file->data->data + written, total - written);
+      if (n <= 0) {
+        ok = false;
+        break;
+      }
+      written += (size_t)n;
+    }
+  }
+  close(fd);
+  free(destination);
+  return ok ? FILE_SAVE_WRITTEN : FILE_SAVE_SKIPPED;
+}
+
 FileSaveResult file_save_to_disk_full(const char* root_directory, const File* file,
                                       const Config* config) {
   /* Backups are incompatible with ignore-existing: moving the entry first
@@ -314,6 +540,14 @@ FileSaveResult file_save_to_disk_full(const char* root_directory, const File* fi
     return FILE_SAVE_ERROR;
   }
 
+  /* Device/special node (--devices/--specials): recreate the node instead of
+     writing content (privilege-gated, confined, rdev-validated). */
+  if (file->is_special)
+    return file_save_special_to_disk(root_directory, file, config);
+  /* --write-devices: write straight into an existing device node. */
+  if (config && config->write_devices)
+    return file_save_write_device(root_directory, file);
+
   /* Explicit directory entries (--dirs) carry an empty payload; the entry is
      created as a directory under the receive root, applying the same secure
      mkdir-parent semantics as regular writes.  Directories are created
@@ -1868,6 +2102,70 @@ File* file_receive_hardlink(int file_descriptor) {
   return file;
 }
 
+/* Receive a device/special node frame (--devices/--specials): the leading
+ * STATUS_SPECIAL code has already been consumed.  Payload: the destination path,
+ * the metadata frame (whose mode's S_IFMT bits carry the node kind), and two
+ * int32 rdev major/minor fields.  The created File carries no payload and is
+ * recreated by file_save_to_disk_full (mknod/mkfifo, privilege-gated and
+ * confined).  rdev is validated here (non-negative, range-checked) so a bogus
+ * value cannot drive a dangerous node on the receiver. */
+File* file_receive_special(int file_descriptor) {
+  char* path = receive_str(file_descriptor);
+  if (path == NULL)
+    return NULL;
+  if (path[0] == '\0' || has_path_traversal(path)) {
+    char* escaped_path = output_escape(path, log_get_8_bit_output());
+    log_message(LOG_LEVEL_ERROR, "Invalid received special path: %s",
+                escaped_path ? escaped_path : "<allocation failed>");
+    free(escaped_path);
+    free(path);
+    send_status(file_descriptor, STATUS_ERROR);
+    return NULL;
+  }
+  int meta_ok = 1;
+  FileMetadata* metadata = metadata_receive(file_descriptor, &meta_ok);
+  if (!meta_ok) {
+    free(path);
+    send_status(file_descriptor, STATUS_ERROR);
+    return NULL;
+  }
+  int32_t major = 0;
+  int32_t minor = 0;
+  if (!receive_n_data(file_descriptor, &major, sizeof(major)) ||
+      !receive_n_data(file_descriptor, &minor, sizeof(minor))) {
+    free(path);
+    file_metadata_destroy(metadata);
+    send_status(file_descriptor, STATUS_ERROR);
+    return NULL;
+  }
+  /* A node kind must be present; without metadata mode there is no S_IFMT to
+     recreate from. */
+  if (!metadata) {
+    log_message(LOG_LEVEL_ERROR, "Special node sent without metadata (mode)");
+    free(path);
+    send_status(file_descriptor, STATUS_ERROR);
+    return NULL;
+  }
+  if (!file_special_rdev_valid(major, minor, metadata->mode)) {
+    log_message(LOG_LEVEL_ERROR, "Invalid special rdev received (%d:%d)", (int)major, (int)minor);
+    free(path);
+    file_metadata_destroy(metadata);
+    send_status(file_descriptor, STATUS_ERROR);
+    return NULL;
+  }
+  File* file = file_create(path);
+  free(path);
+  if (file == NULL) {
+    file_metadata_destroy(metadata);
+    return NULL;
+  }
+  file->metadata = metadata;
+  file->is_special = true;
+  file->rdev_major = major;
+  file->rdev_minor = minor;
+  return file;
+}
+
 /* Read a delete-manifest frame (the STATUS_MANIFEST leading code has already
    been consumed): a keep-set entry count followed by that many
    destination-relative paths, then a protected-prefix count followed by that

src/shared/file_receive.h

@@ -10,6 +10,8 @@
 File* file_receive(const Config* config, int file_descriptor);
 File* file_receive_directory(int file_descriptor);
 File* file_receive_hardlink(int file_descriptor);
+File* file_receive_special(int file_descriptor);
+bool file_special_rdev_valid(int32_t major, int32_t minor, mode_t mode);
 File* receive_incremental_check(int fd, const Config* config, bool* skipped);
 
 /* A received delete-manifest frame: the keep-set (`keeps`, destination-relative

src/shared/file_send.c

@@ -17,6 +17,25 @@
 #include "metadata.h"
 #include "protocol.h"
 
+/* Transmit a device/special node (--devices / --specials) as a STATUS_SPECIAL
+ * frame: the destination path, the metadata frame (whose mode's S_IFMT bits
+ * carry the node kind) and the device rdev major/minor.  The receiver validates
+ * the kind and rdev and recreates the node (privilege-gating the mknod). */
+bool file_send_special(File* file, int file_descriptor, bool use_metadata) {
+  if (!file || !file_wire_path(file))
+    return false;
+  if (!send_status(file_descriptor, STATUS_SPECIAL))
+    return false;
+  if (!send_str(file_descriptor, file_wire_path(file)))
+    return false;
+  if (use_metadata && !metadata_send(file_descriptor, file->metadata))
+    return false;
+  int32_t major = file->rdev_major;
+  int32_t minor = file->rdev_minor;
+  return send_n_data(file_descriptor, &major, sizeof(major)) &&
+         send_n_data(file_descriptor, &minor, sizeof(minor));
+}
+
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path) {
   return file_send_single_calls_with_skip(file, file_descriptor, use_metadata, compression_level,

src/shared/file_send.h

@@ -6,6 +6,7 @@
 
 /* Client-side file send path. */
 
+bool file_send_special(File* file, int file_descriptor, bool use_metadata);
 bool file_send_single_calls(File* file, int file_descriptor, bool use_metadata,
                             int compression_level, bool send_path);
 bool file_send_single_calls_with_skip(File* file, int file_descriptor, bool use_metadata,

src/shared/file_types.h

@@ -56,6 +56,15 @@ typedef struct {
   int link_group;
   bool link_first;
   char* hardlink_target;
+  /* Phase 4 special/devices: when `is_special` is true this entry is a device
+   * or special node to be RECREATED on the destination (mknod/mkfifo) rather
+   * than written from `data`.  The concrete node kind is derived from the
+   * metadata mode's S_IFMT bits (receiver-validated), and rdev_major/minor
+   * carry the device major/minor numbers for char/block devices.  CROSSES the
+   * wire (protocol 2.13.0). */
+  bool is_special;
+  int32_t rdev_major;
+  int32_t rdev_minor;
 } File;
 
 /* The path that should be sent on the wire and used for the receiver-side

src/shared/multiprocessing.c

@@ -308,8 +308,9 @@ int write_thread(void* pipeline_context) {
     }
     /* Record the per-file outcome so a --remove-source-files sender learns
        which sources were actually written versus skipped on the receiver.
-       Explicit directory entries have no source and are never acknowledged. */
-    if (context->config->remove_source_files && !file->is_dir && !file->skip &&
+       Explicit directory entries and recreated device/special nodes have no
+       source and are never acknowledged (mirrors receiver.c). */
+    if (context->config->remove_source_files && !file->is_dir && !file->is_special && !file->skip &&
         !receiver_outcomes_append(&context->outcomes, (unsigned char)result)) {
       file_destroy(file);
       pipeline_context_receiver_note_bytes_released(context, file_bytes);

src/shared/protocol.h

@@ -90,7 +90,14 @@ enum NET_STATUS {
    * first (data-carrying) member's destination-relative wire path; the receiver
    * creates this entry as a hard link to the first member's installed file
    * (falling back to a byte-identical copy if link() fails).  Protocol 2.12.0. */
-  STATUS_HARDLINK
+  STATUS_HARDLINK,
+  /* --devices / --specials (-D): a device or special node the sender wants
+   * recreated (not written from content).  Payload: destination path, the
+   * metadata frame (whose mode's S_IFMT bits carry the node kind), and two
+   * int32 rdev major/minor fields.  The receiver validates the kind and rdev,
+   * confines the node below the receive root, and recreates it (mknod/mkfifo),
+   * privilege-gating the mknod.  Protocol 2.13.0. */
+  STATUS_SPECIAL
 };
 
 void io_set_fds(int read_fd, int write_fd);