fix: distinguish supported network backup mounts from local filesystems

backups.py

@@ -3,7 +3,7 @@ import datetime as dt
 from contextlib import closing
 import hashlib
 import os
-from pathlib import Path
+from pathlib import Path, PurePosixPath
 import re
 import secrets
 import shutil
@@ -27,6 +27,33 @@ class Backups:
                     last=self.a.setting('backup_last', None),
                     history=self.a.setting('backup_history', [])[-20:][::-1])
 
+    @staticmethod
+    def network_mount(folder):
+        if os.name == 'nt':
+            return folder.drive.startswith('\\\\')
+        try:
+            records = Path('/proc/self/mountinfo').read_text().splitlines()
+        except OSError:
+            return False
+        return Backups.linux_network_mount(PurePosixPath(str(folder)), records)
+
+    @staticmethod
+    def linux_network_mount(folder, records):
+        matches = []
+        for line in records:
+            left, separator, right = line.partition(' - ')
+            fields, detail = left.split(), right.split()
+            if not separator or len(fields) < 5 or not detail:
+                continue
+            mount = PurePosixPath(re.sub(r'\\([0-7]{3})', lambda m: chr(int(m[1], 8)), fields[4]))
+            if folder.is_relative_to(mount):
+                matches.append((len(mount.parts), detail[0]))
+        # The nearest mount wins: a tmpfs inside an NFS share is still local.
+        filesystem = max(matches, default=(0, ''), key=lambda x:x[0])[1]
+        return filesystem in {'cifs', 'smb3', 'nfs', 'nfs4', 'davfs',
+                              'fuse.sshfs', 'fuse.rclone', 'fuse.davfs', 'fuse.davfs2',
+                              'fuse.wdfs', 'fuse.s3fs', 'fuse.goofys'}
+
     def network_folder(self, text):
         if not text:
             return None
@@ -39,8 +66,8 @@ class Backups:
         if not folder.is_dir():
             raise self.a.Problem('备份目录不存在，请先在服务器挂载网络存储并授予服务账号写入权限')
         # A disconnected mount must not silently become a local-only cloud backup.
-        if not any(os.path.ismount(p) for p in (folder, *folder.parents) if p != Path(p.anchor)):
-            raise self.a.Problem('该目录尚未检测到独立挂载；请先连接网络盘，不能把本机目录当作云端成功')
+        if not self.network_mount(folder):
+            raise self.a.Problem('该目录未检测到支持的网络挂载，请先连接 NFS、SMB、WebDAV 或 rclone 网络盘')
         if folder == (self.a.DATA/'managed-backups').resolve():
             raise self.a.Problem('网络副本与本机备份目录不能相同')
         return folder