Handle cross-subvolume moves safely using execv mv fallback

src/main.c

@@ -1,7 +1,7 @@
 /*
 This file is part of rmw<https://theimpossibleastronaut.github.io/rmw-website/>
 
-Copyright (C) 2012-2023  Andy Alt (arch_stanton5995@proton.me)
+Copyright (C) 2012-2025  Andy Alt (arch_stanton5995@proton.me)
 Other authors: https://github.com/theimpossibleastronaut/rmw/blob/master/AUTHORS.md
 
 This program is free software: you can redistribute it and/or modify
@@ -262,7 +262,6 @@ list_waste_folders(st_waste *waste_head)
   return;
 }
 
-
 static int
 remove_to_waste(const int argc,
                 char *const argv[],
@@ -412,12 +411,26 @@ damage of 5000 hp. You feel satisfied.\n"));
         int r_result = 0;
         if (cli_user_options->want_dry_run == false)
         {
-          if ((waste_curr->dev_num != st_target.dev_num) && !S_ISDIR(st_file_arg.st_mode))
+          int save_errno = errno;
+          const char *src = argv[file_arg];
+          const char *dst = st_target.waste_dest_name;
+
+          if (waste_curr->dev_num != st_target.dev_num)
           {
-            int save_errno = errno;
-            r_result =
-              do_btrfs_clone(argv[file_arg], st_target.waste_dest_name,
-                             &save_errno);
+            /* cross-device: different device numbers */
+            if (!S_ISDIR(st_file_arg.st_mode))
+            {
+              /* attempt btrfs clone if not a directory */
+              r_result = do_btrfs_clone(src, dst, &save_errno);
+              errno = save_errno;
+            }
+            else
+            {
+              /* directory on different device: call /bin/mv safely */
+              r_result = safe_mv_via_exec(src, dst, &save_errno);
+              errno = save_errno;
+            }
+
             if (r_result != 0)
             {
               if (save_errno == EXDEV)
@@ -426,12 +439,16 @@ damage of 5000 hp. You feel satisfied.\n"));
                 continue;
               }
               else
+              {
                 exit(EXIT_FAILURE);
+              }
             }
           }
           else
           {
-            r_result = rename(argv[file_arg], st_target.waste_dest_name);
+            /* same device: simple rename */
+            r_result = rename(src, dst);
+            /* rename sets errno on failure */
           }
         }
 

src/restore.c

@@ -1,7 +1,7 @@
 /*
 This file is part of rmw<https://theimpossibleastronaut.github.io/rmw-website/>
 
-Copyright (C) 2012-2023  Andy Alt (arch_stanton5995@proton.me)
+Copyright (C) 2012-2025  Andy Alt (arch_stanton5995@proton.me)
 Other authors: https://github.com/theimpossibleastronaut/rmw/blob/master/AUTHORS.md
 
 This program is free software: you can redistribute it and/or modify
@@ -63,6 +63,67 @@ get_waste_parent(char *waste_parent, const char *src)
   return;
 }
 
+static int
+move_back(const char *src, const char *dest, bool want_dry_run)
+{
+  int rename_res = 0;
+  int save_errno = 0;
+  int clone_errno = 0;
+
+  if (want_dry_run)
+    return 0;
+
+  rename_res = rename(src, dest);
+  if (rename_res == 0)
+    return 0;                   /* success */
+
+  /* rename failed; preserve errno immediately */
+  save_errno = errno;
+
+  struct stat st_src;
+
+  /* rename already failed and save_errno == errno from rename() */
+  if (save_errno == EXDEV)
+  {
+    /* get file type without following symlinks */
+    if (lstat(src, &st_src) != 0)
+    {
+      /* cannot stat. restore rename's errno and fail */
+      errno = save_errno;
+      return -1;
+    }
+
+    if (S_ISDIR(st_src.st_mode))
+    {
+      /* directory on different device -> execv mv */
+      int mv_ret = safe_mv_via_exec(src, dest, &clone_errno);
+      if (mv_ret == 0)
+      {
+        errno = 0;
+        return 0;
+      }
+      errno = clone_errno ? clone_errno : save_errno;
+      return -1;
+    }
+    else
+    {
+      /* regular file on different device -> try btrfs clone */
+      int clone_res = do_btrfs_clone(src, dest, &clone_errno);
+      if (clone_res == 0)
+      {
+        errno = 0;
+        return 0;
+      }
+      errno = clone_errno ? clone_errno : save_errno;
+      return -1;
+    }
+  }
+
+  /* other rename error */
+  errno = save_errno;
+  return -1;
+}
+
 
 int
 restore(const char *src, st_time *st_time_var,
@@ -171,16 +232,10 @@ Duplicate filename at destination - appending time string...\n"));
         return p_state_parent;
     }
 
-    int rename_res = 0;
-    int save_errno = errno;
-    if (cli_user_options->want_dry_run == false)
-    {
-      rename_res = rename(src, dest);
-      if (errno == EXDEV)
-        rename_res = do_btrfs_clone(src, dest, &save_errno);
-    }
+    int res = move_back(src, dest, cli_user_options->want_dry_run);
+
 
-    if (!rename_res)
+    if (!res)
     {
       printf("+'%s' -> '%s'\n", src, dest);
 
@@ -199,7 +254,7 @@ Duplicate filename at destination - appending time string...\n"));
     else
     {
       msg_err_rename(src, dest);
-      return rename_res;
+      return res;
     }
   }
   else

src/utils.c

@@ -1,7 +1,7 @@
 /*
 This file is part of rmw<https://theimpossibleastronaut.github.io/rmw-website/>
 
-Copyright (C) 2012-2023  Andy Alt (arch_stanton5995@proton.me)
+Copyright (C) 2012-2025  Andy Alt (arch_stanton5995@proton.me)
 Other authors: https://github.com/theimpossibleastronaut/rmw/blob/master/AUTHORS.md
 
 This program is free software: you can redistribute it and/or modify
@@ -21,6 +21,8 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifndef INC_GLOBALS_H
 #define INC_GLOBALS_H
 
+#include <sys/wait.h>
+
 #include "globals.h"
 #endif
 
@@ -495,6 +497,67 @@ count_chars(const char c, const char *str)
 }
 
 
+/* returns 0 on success, non-zero on failure.
+   On error sets *out_errno when out_errno != NULL. */
+int
+safe_mv_via_exec(const char *src, const char *dst, int *out_errno)
+{
+  pid_t pid;
+  int status;
+  int saved_errno = 0;
+
+  pid = fork();
+  if (pid < 0)
+  {
+    saved_errno = errno;
+    if (out_errno)
+      *out_errno = saved_errno;
+    return -1;
+  }
+
+  if (pid == 0)
+  {
+    /* child: exec /bin/mv directly (argv[0] is "mv") */
+    char *const argv_mv[] = { "mv", (char *) src, (char *) dst, NULL };
+    execv("/bin/mv", argv_mv);
+    /* if execv fails, set errno and exit with a distinct code */
+    _exit(127);
+  }
+
+  /* parent: wait for child */
+  if (waitpid(pid, &status, 0) < 0)
+  {
+    saved_errno = errno;
+    if (out_errno)
+      *out_errno = saved_errno;
+    return -1;
+  }
+
+  if (WIFEXITED(status))
+  {
+    int code = WEXITSTATUS(status);
+    if (code == 0)
+    {
+      if (out_errno)
+        *out_errno = 0;
+      return 0;
+    }
+    /* child program returned nonzero. we cannot see its errno.
+       map common mv exit codes to errno conservatively. */
+    saved_errno = EIO;
+    if (out_errno)
+      *out_errno = saved_errno;
+    return code;
+  }
+
+  /* child was terminated by signal */
+  saved_errno = EINTR;
+  if (out_errno)
+    *out_errno = saved_errno;
+  return -1;
+}
+
+
 ///////////////////////////////////////////////////////////////////////
 #ifdef TEST_LIB
 

src/utils.h

@@ -1,7 +1,7 @@
 /*
 This file is part of rmw<https://theimpossibleastronaut.github.io/rmw-website/>
 
-Copyright (C) 2012-2024  Andy Alt (arch_stanton5995@proton.me)
+Copyright (C) 2012-2025  Andy Alt (arch_stanton5995@proton.me)
 Other authors: https://github.com/theimpossibleastronaut/rmw/blob/master/AUTHORS.md
 
 This program is free software: you can redistribute it and/or modify
@@ -64,4 +64,6 @@ bool is_dir_f(const char *pathname);
 
 int count_chars(const char c, const char *str);
 
+int safe_mv_via_exec(const char *src, const char *dst, int *out_errno);
+
 #endif

test/conf/btrfs_img.testrc

@@ -1,5 +1,4 @@
 #waste = /tmp/rmw-loop/.Trash-$UID
-waste = /tmp/rmw-loop/three/Waste
 waste = /tmp/rmw-loop/@two/Waste
 waste = /tmp/rmw-loop/trashlink
 WASTE = $HOME/.local/share/Waste

test/test_btrfs_clone.sh

@@ -28,20 +28,22 @@ fi
 cd "$BTRFS_IMAGE_MOUNTPOINT"
 RMW_TEST_CMD_STRING="$BIN_DIR/rmw -c ${MESON_SOURCE_ROOT}/test/conf/btrfs_img.testrc"
 
-SUBVOLUME_USED="/tmp/rmw-loop/three"
+SUBVOLUME_USED="/tmp/rmw-loop/@two"
 
 WASTE_USED="$SUBVOLUME_USED/Waste"
 if [ -d "$WASTE_USED" ]; then
   rm -rf "$WASTE_USED"
 fi
 
-TEST_DIR="$SUBVOLUME_USED/test_dir"
+TEST_DIR="$BTRFS_IMAGE_MOUNTPOINT/test_dir"
 if [ -d "$TEST_DIR" ]; then
   rm -rf "$TEST_DIR"
 fi
 
 mkdir "$TEST_DIR"
-$RMW_TEST_CMD_STRING -v "$TEST_DIR"
+$RMW_TEST_CMD_STRING "$TEST_DIR"
+
+$RMW_TEST_CMD_STRING -u
 
 touch foo
 $RMW_TEST_CMD_STRING foo