If files are accidentally or maliciously deleted from a file system, the user data may be permanently lost. The Trash Can is a useful feature in file systems that acts as a temporary holding area, allowing users to store deleted files for a short time before they are permanently deleted. It provides a mechanism to restore or retrieve deleted files if needed, and automatically deletes the files once they become too old or the filesystem is too full.
When the Trash Can feature is enabled, when a user deletes a file from a file system, it is not immediately deleted but moved to the Trash Can. Deleted files and directories are temporarily stored in the Trash Can. Files and directories in the Trash Can may be restored or retrieved individually or in bulk if they are still available. The Trash Can may be manually emptied, or once the filesystem is nearly full the system will automatically empty files from the Trash, taking into account which users and projects are consuming the most space.
The Trash Can should including the following functionalities:
rm or rmdir utility or unlink() and rmdir() syscalls, or if a file is renamed onto another one).Restore a file in the Trash Can. This will restore a file or directory to its original path. The corresponding User, Group, and Project quota account should also be increased again.
After a file is deleted and moved into Trash Can, the User, Group, and Project quota for this file should be accounted and reduced accordingly.
A file in the Trash Can is not visible in the namespace of the file system.
TRASH flag, so that tools like lipe_find3 can optionally skip/find deleted files.TRASH flag cannot be read by a user or application, to prevent applications continuing to read these files.Permanently remove a file in the Trash Can. This will remove the file from the Trash can and destroy the OST objects to free the used space. The file is now unrecoverable.
Empty the Trash Can. This will remove all files in the Trash Can.
Files should be deleted from Trash Can after a specified retention period, such as 7 days.
Have a tunable parameter to enable/disable Trash Can feature on a entire file system.
A administrator can enable/disable Trash Can feature on a specified file or directory by setting the NOTRASH flag on the file.
Deleted files can no longer be restored from the Trash Can when:
A file (or directory) is deleted from the Trash Can. In other words it have been deleted twice. The first deletion only moves the file to the Trash Can. The second deletion actually removes the file from the file system.
The Trash Can is emptied of all of its contents.
The design for the Trash Can feature in Lustre is relatively straight forward.
On the server side, the MDS implements the basic functionalities such as moving the "deleted" files into the Trash Can, and the interface how to traverse them. On the client side, it implements the basic utility tools to interact with the Trash Can ("lfs trash set|clear|list|delete|restore FILE|DIR"), including:
TRASH flag on a given file or directoryOur mechanism only moves the regular files into the Trash Can upon its last unlink, but ignoring the directories.
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" 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 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.recyclebin"); 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.recyclebin")/close()/closedir().
The workflow for the Trash Can is as follows:
An administrator can enable/disable Trash Can feature on a specified MDT via: lctl set_param mdd.*.enable_trash_can
An adminstrator can enable/disable Trash Can feature on a specified directory or a file via the file flag: FS_UNRM_FL; All sub files under a directory flagged with FS_UNRM_FL can inherit this flag;
# lfs trash set $file|$dir
# lfs trash clear $file|$dirMove a deleting file into the Trash Can. When delete a regular file marked with FS_UNRM_FL upon its last unlink, first move the file into the Trash Can directory "ROOT/RECYCLE" with FID as its name. And then set a "trusted.unrm" XATTR on the "undeleted" file on the Trash Can. The XATTR contains the following information:
struct ll_trash_xattr {
__u32 ltx_flags;
__u32 ltx_uid; // UID of the deleting file, used for quota accounting
__u32 ltx_gid; // gid of the deleting file, used for quota accounting
__u32 ltx_projid; // projid of the deleting file, used for quota accounting
__u64 ltx_timestamp; // Timestamp that the file moved into the Trash Can, maybe we could use ctime here
};Where ltx_uid/ltx_gid/ltx_projid are the original UID/GID/PROJID of the deleted file, mainly used for quota accounting for the restore operation; @ltx_timestamp is the time that the file was moved into the Trash Can. It is used to determine whether the file is expired for the specified retention period and thus should be removed from the Trash Can finially (maybe we could also use the inode ctime for this purpose instead of storing a separate timestamp?). During deleting the file, we can get the full path information via the way similar to fid2path().
List "undeleted" files within a Trash Can. By default it will list files/directories deleted relative to the current working directory. If DIR is provided, then list deleted files/directories relative to that directory, in the same format as ls:
# lfs trash {list|ls} [DIR|FILE]
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
...
Internally, the lfs trash list command is looking up the FID and MDT of the current directory, or the directory specified by DIR, and then listing the respective directory under $MOUNT/.lustre/trash/MDTxxxx/DIRFID/ or the directory file descriptor returned via llapi_recycle_fid_get(MNTPT, mdt) if the .lustre/trash directory is not available.
where any files deleted from this directory would be moved.
Deleting a file or directory in the Trash Can will remove the temporary file under "ROOT/TRASH" and free the data space on Lustre OSTs permanently:
# lfs trash {delete|rm} [DIR/]FILE ...Empty a Trash Can:
# lfs trash clear DIR ...
Restore a file in the Trash Can on a given MDT. It will restore the file and its content according to the saved full path and then delete the stub on the Trash Can.
# lfs trash {restore|unrm} [DIR/]FILE ...A utility periodically scans the files under Trash Can directory "ROOT/TRASH" and delete the file with grace time expiration.
Provide the functionality to scan files in the trash on all MDTs that exceed the specified age manually:
# lfs trash find -ctime +time [DIR]Provide the functionality to restore/delete all files within a given directory. This can be achieved by using the command combination of "lfs trash list" and "lfs trash restore" or "lfs trash delete" to filter the files with the full path attribute under a given directory.
Provide .lustre/trash/MDTnnnn (where nnnn is the MDT index) filesystem namespace. By this way, users can access the "undeleted" files with readonly mode under the Trash Can directory on a given MDTnnnn via POSIX file system API. However, we can not access these files from fileset sub directory mount. We can perform the following commands from a Lustre namespace (mount point of "/mnt/lustre") on a client:
# ls /mnt/lustre/.lustre/trash/MDT0002
0x200034021:0x1:0x0
0x200034021:0x2:0x0
...
# lfs trash ls /mnt/lustre/.lustre/recycle/MDT0002/0x200034021:0x1:0x0
0 0 4096 Nov 14 08:11 [0x200034021:0x1:0x0]->/mnt/lustre/f1
# lfs trash list /mnt/lustre/.lustre/recycle/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
...
It needs to automatically clean up files from the trash can when the filesystem becomes full. It cannot be that the user has to delete every file twice, and it cannot be that the filesystem is allowed to get 100% full (or even 90% full) due to files in the trash. There needs to be an automatic mechanism to clean up the trash to ensure that the filesystem performance does not degrade when users though they deleted files.
It can assign the UID/GID/PROJID to a trash user so that this quota is not accounted against the end user, and keep the original UID/GID/PROJID in a the XATTR "trusted.unrm".
In our design, it does not depend on a userspace utility for such a critical function to clean up files from the trash when FS is nearly full, since that utility may never be started, or the client is evicted, or similar. If that happens, the filesystem would become full and unusable, even though the user had already deleted files from the filesystem. This needs to be bulletproof and run automatically when the OSTs (or MDTs) are getting full.
The MDS is already monitoring the OST fullness every 5s to make object allocation decisions, so it can also make decisions about files to delete.Thus MDT can periodically monitor the space usage of the trash user (quota) and space usage for the entire file system with the additional consideration of the retention period and deleted timestamp for the files, choose the candidates to be deleted permanently to free up the space.
Also, there needs to be some accounting of files in the trash, so that "df" does not show the filesystem as 100% or 90% full all the time, but rather show only the non-trash space usage (= real usage - trash usage).
It can define a per-user TRASH/UID directory that is owned by that UID and mode 0600 to avoid world readable access. That avoids exposing files to other users that may be private, and also allows tracking space usage more clearly for each UID, so that a user's data can be purged more quickly if they are exceeding their quotas.