On Thu, Jan 19, 2017 at 2:13 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > Miklos, > > I implemented freeze/thaw of overlayfs, because I need it for > overlay snapshots (CoW decision is made before mnt_wat_write(upper) > and I need to serialize it with snapshot take). > Miklos, Jan, I would be grateful if you guys could help me clarify something wrt freezefs vs. remount. I hope you may be able to enlighten me with just the information provided in this email without having to dive into overlayfs snapshot details. I implemented 'snapshot take' for overlayfs snapshots using a command like: mount -o remount,snapshot=/snap/N /mnt The 'snapshot take' moment from overlayfs writers perspective is when a single pointer is modified via rcu_assign_pointer(ufs->__snapmnt, snapmnt): https://github.com/amir73il/linux/commit/f0d6759efb7a6281ecc55dcdf33837568f71d29a I chose to use the remount_fs() API because it is convenient and make sense from user POV, but I could also use some IOCTL API for snapshot take. For consistency of snapshot from application POV, I need to do: fsfreeze -f snapshot take fsfreeze -u But then I cannot use the remount_fs() API which requires that fs be unfrozen. Can you please explain why do_remount_sb() requires that fs be unfrozen? Would it be possible to relax this requirement depending on remount flags? The reason I ask is because overlay remount does not do any writes nor call mnt_want_write() for that matter. Thanks, Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
