On Tue, 2021-04-13 at 17:46 -0400, Ramana Venkatesh Raja wrote: > Hi, > > I'd questions around feature tracker, > https://tracker.ceph.com/issues/10679 that requests for chattr +i > support in cephfs, and wanted to check whether the earlier discussed > approach is still good [1]. > > A while ago, John Spray suggested that the S_IMMUTABLE flag be stored > in the high bits of the cephfs inode's mode attribute as the inode > doesn't have the i_flags attribute. The cephfs inode's mode attribute > has 32 bits, and seems like only 16 bits are used for access modes and > file type. In comparison, ext4 inode's mode attribute and i_flags > attribute are 16 bits and 32 bits respectively. Should we store the > S_IMMUTABLE flag in the mode attribute, or in a new i_flags attribute? > I wouldn't overload it onto the mode field. That's "clever" but not particularly helpful. I think the main place you're going to need to store this is in struct inode_t, right? If so, then there are some existing holes in that structure that you could use to add a new flags field (or maybe just an immutable bool) without growing it. In practice, _storing_ this info is not going to be too difficult, I think. The harder part here is revving the protocol to carry this flag in the appropriate network messages, and fixing up the client and MDS to handle it. > e2fsprogs' chattr uses FS_IOC_[GS]ETFLAGS ioctls to get/set the > S_IMMUTABLE flag of an inode. The two ioctls need to be added to the > kernel and FUSE clients as mentioned in [2]. Maybe later if required > we can add the FS_IOC_FS[GS]ETXATTR ioctls [3] that can also get/set > inode flags. What interfaces should libcephfs use to get/set the > immutable bit flag? > You'll probably want to add a new call to libcephfs for this (ceph_set_immutable() or something). > Sage suggested that the MDS check for the S_IMMUTABLE flag, and not > issue write caps if set, and the clients also check for the flag and > return suitable errno to avoid waiting for the caps. Does this > enforcement sound good? Note that data of immutable files can be > modified using open fds existing prior to the immutable flag being set > on files in linux file systems[4]. > Yeah, that sounds fine. > [1] https://www.spinics.net/lists/ceph-users/msg15221.html > [2] https://www.spinics.net/lists/ceph-users/msg15224.html > [3] https://lore.kernel.org/linux-fsdevel/1451886892-15548-1-git-send-email-david@xxxxxxxxxxxxx/ > [4] https://lwn.net/Articles/786258/ > _______________________________________________ > Dev mailing list -- dev@xxxxxxx > To unsubscribe send an email to dev-leave@xxxxxxx > -- Jeff Layton <jlayton@xxxxxxxxxx> _______________________________________________ Dev mailing list -- dev@xxxxxxx To unsubscribe send an email to dev-leave@xxxxxxx
