Merge feat/p4-devices

# Conflicts:
#	src/client/client_send.c
#	src/server/receiver.c
#	src/shared/chunk.c
#	src/shared/file.c
#	src/shared/file_receive.c
#	src/shared/file_receive.h
#	src/shared/file_types.h
#	src/shared/protocol.h
#	tests/test_chunk.c

src/client/client_cli.c

@@ -540,6 +540,11 @@ 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)},
@@ -834,6 +839,12 @@ 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;
@@ -1203,6 +1214,15 @@ 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

@@ -106,6 +106,9 @@ static bool prepare_scanner(const Config* config, int num_threads, PreparedScann
   options->munge_links = config->munge_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;
@@ -1264,13 +1267,21 @@ static int send_chunk_with_removal(Client* client, Chunk* chunk, Config* config,
       change_emit_file_sent(config, f);
       continue;
     }
-    /* Symlink entry (-l / -k keep-as-symlink): only the target rides the wire. */
+/* Symlink entry (-l / -k keep-as-symlink): only the target rides the wire. */
     if (f->is_symlink) {
       if (!send_symlink_entry(client, f, config))
         return -1;
       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>
@@ -199,6 +200,34 @@ 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). */
@@ -420,6 +449,9 @@ DirectoryScanner* directory_scanner_create_with_options(const char* root_directo
   scanner->munge_links = options->munge_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) {
@@ -990,6 +1022,9 @@ 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)
@@ -1316,6 +1351,7 @@ 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

@@ -42,6 +42,12 @@ typedef struct {
   bool munge_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). */
@@ -114,6 +120,10 @@ 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

@@ -185,6 +185,15 @@ void print_usage(void) {
   printf("  --munge-links       Munge symlink targets on the wire (sender)\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");