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It borrows lots of ideas from orphan and volatile files in Lustre (which stores in "ROOT/PENDING" directory on each MDT). During the format and setup, each MDT creates a "ROOT/TRASH.lustre/Trash" directory as a Trash Can to store "undeleted" files.

The POSIX API is used to traverse the files under the Trash Can on a given MDT. First, a client can get the FID of Trash Can directory ROOT/TRASH on .lustre/Trash on the MDT. Then the client can get the file handle via FID open: dir_fd=llapi_open_by_fid(). After that, the "undeleted" files within the Trash Can can be traversed via readdir(dir_fd); it can open by openat(dir_fd, ent->d_name) and obtain the "trusted.unrm" XATTR, which contains the necessary information to resotre, via fgetxattr(fd, "trusted.recyclebinunrm"); The client can even read the data or swap layouts of the "undeleted" file on the Trash Can for restore: opendir()/readddir()/openat()/fgetxattr("trusted.recyclebinunrm")/close()/closedir().

The workflow for the Trash Can is as follows:

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     # ls /mnt/lustre/.lustre/trashTrash/MDT0002

     0x200034021:0x1:0x0
     0x200034021:0x2:0x0
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     # lfs trash ls /mnt/lustre/.lustre/recycleTrash/MDT0002/0x200034021:0x1:0x0
     0 0 4096 Nov 14 08:11 [0x200034021:0x1:0x0]->/mnt/lustre/f1
     # lfs trash list /mnt/lustre/.lustre/recycleTrash/MDT0002
     MDT index: 1
     uid gid   size delete time FID                    Fullpath
     0 0 4096  Nov 14 08:11     [0x200034021:0x1:0x0]->/mnt/lustre/f1
     0 0 32104 Nov 14 08:07     [0x200034021:0x2:0x0]->/mnt/lustre/dir/f2
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