Probably it makes sense for Shilong to raise this issue on linux-fsdevel and bug-tar mailing lists to see if there is a preferred solution to saving/restoring the projid. I think that since the ioctl() interface is existingfor all filesystems using projid that it makes sense for tar to use this interface, but it would mean we need to patch tar until it is accepted into upstream versions/distros.
Providing an xattr to get/set the projid would be more compatible with other tools (even symlinks, I think), but it would mean changes to all filesystems using projid.
Currently, I think solution might be to use get ioctl to grab project of directories and files and to use
set ioctl to set it, this won't work for symlink files until project ID for symlink files support landed.
I would think it makes more sense to add complete support to tar after symlink files support land too.
I think it would be relatively straight forward to expose a virtual xattr trusted.projid that returns only the ASCII-formatted projid value from i_projid in the inode, or nothing if it is zero. When written, it will convert the ASCII number to binary and store it in i_projid in the inode, similar to what FS_IOC_FSGETXATTR does.
This would immediately work with all backup tools, and would not need much code in ldiskfs, and would likely be accepted upstream as well.
It may also make sense to expose the inode flags via trusted.attrflags so that they are reliably backed up and restored as well.
Yup, acutally, i've made this similar idea patch long time ago, but not push it out.
Shilong, you mentioned here that you have a patch that presents the projid as a virtual xattr to userspace. Do you still have that patch?
Hi Dongyang,
could you please look into an ldiskfs patch to expose the projid as a virtual trusted.projid that contains the ASCII project ID, so that normal tools like tar and rsync can backup and restore it. The use of trusted should limit this access to the root user, which is fine for us, and avoids the issue of non-root users using setfattr to set the projid on a file.
If ldiskfs is exposing the trusted.projid xattr in the xattr list, then this should also be visible to root at the client without any need for changes.
"Li Dongyang <dongyangli@ddn.com>" uploaded a new patch: https://review.whamcloud.com/45679
Subject: LU-12056 ldiskfs: add trusted.projid virtual xattr
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 34a9711a083a0d8a311b7caf2aaf444568eb6f83
"Oleg Drokin <green@whamcloud.com>" merged in patch https://review.whamcloud.com/45679/
Subject: LU-12056 ldiskfs: add trusted.projid virtual xattr
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 665383d3a1f4d1dc7f404301039432271ad85eaf
Landed for 2.15
"Li Dongyang <dongyangli@ddn.com>" uploaded a new patch: https://review.whamcloud.com/46295
Subject: LU-12056 ldiskfs: add ext4-projid-xattrs.patch for Linux 5.10
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 4086dcc2cd0757b3738cf32972020c6a54f1486d
"Oleg Drokin <green@whamcloud.com>" merged in patch https://review.whamcloud.com/46295/
Subject: LU-12056 ldiskfs: add ext4-projid-xattrs.patch for Linux 5.10
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 46a28ae19f38f8959986dcce2b331ac7e48886fc