Reported by an OEM.

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We use dirsort module in our product, and encounter some problems with
this module.
Since dirsort module only keeps one private data (i.e., struct
dirsort_privates) for per vfs_handle_struct.
Once the samba process calls SMB_VFS_OPENDIR multiple times, the previous data
will be overwritten, like the following example:

dirp1 = SMB_VFS_OPENDIR(dir_a);
dirp2 = SMB_VFS_OPENDIR(dir_b);
...
SMB_VFS_READDIR(dirp1); // this will get wrong results since the data was
overwritten in the second SMB_VFS_OPENDIR()
SMB_VFS_READDIR(dirp2);
...
SMB_VFS_CLOSEDIR(dirp2);
SMB_VFS_CLOSEDIR(dirp1);

According to our experiences, this scenario sometimes happens when users use 7-
zip to compress a big direcotry (i.e., a directory which contains many sub
folders and sub-sub folders).
Since dirsort module returns a wrong file list, users will get incorrect
archive files.
We think the private data should be stored for per dir pointer so that it will
not be overwritten by the other SMB_VFS_OPENDIR().

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I have a fix for this to follow.