On Fri, May 19, 2017, at 12:34 PM, Colin Walters wrote: > > So as far as I can see, a userspace API to ensure the journal is > flushed on a mounted filesystem is going to be necessary for > the general case. I don't have a strong opinion on whether or not > that's `syncfs()` - if it's e.g. a `XFS_IOC_FREEZE` `_THAW` pair > that seems OK to me too. Or (thinking about this more) maybe we indeed could implement that today by pivoting back to the initramfs, and using umount()+mount() as our "syncfs() + journal flush" implementation. Basically when we have to update /boot, we unmount, then remount again and add new kernel+initramfs, unmount, remount and mv(/boot/grub2.conf.new,/boot/grub2.conf), then finally unmount again. In current design this would require keeping the initramfs resident in memory just for this purpose, or to re-synthesize it on shutdown. Not impossible, but it'd sure be simpler if say syncfs() had a flags argument and there were a special "flush the journal" argument for this.
