Fixing the filesystem freeze API - Fernando Luis Vazquez Cao, NTT Data Intellilink
Channel: Linux Plumbers Conference
Date: 2013-10-15

In a previous Linux Plumbers Conference (2011) we discussed the serious problems of the Linux kernel's filesystem freeze functionality (among them: there is no check API, which means there is no easy way to know whether a filesystem is frozen or not; it is possible to umount a frozen filesystem despite the fact that there is no API to thaw an unmounted filesystem; it is not possible to freeze multi-device filesystems such as BTRFS; it does not play well with DM snapshot), which make it the weak link in any storage snapshot/backup solution that uses it to put the filesystems in a quiesced state before doing its job. In virtualization environments where the filesystem freeze operation is often controlled by virtualization management software through a guest agent things can easily go awry. http://etherpad.osuosl.org/lpc2013-virtualization http://www.linuxplumbersconf.org/2013/