[systemd-devel] [RFC][PATCH] Add option to enable COW for journal file

[Goffredo Baroncelli]

Hi All,
the enclosed patches add an option to the journald.conf file to allow
a COW behavior for the journal files.

The commit 11689d2a force the NOCOW flag of the journal files. This was 
needed because systemd-journald has very poor performance when the
filesytem is BTRFS due to its the COW behavior.

However removing the COW behavior, the journal file also lost  the
btrfs checksum protection, and this disables the BTRFS capability to rebuild a
corrupted file [1] in a RAID filesystem. So this limits one of the biggest
benefit of BTRFS.
    
This patch adds the option "CowJournal" to the journald.conf to disable/enable
the NOCOW flag for the journal file, allowing to revert to the old behavior.

These patches are tagged as RFC, because I am not sure about the
naming of the option (now "CowJournal"). I ask some feedback.

Comments are welcome.
    
[1] http://en.wikipedia.org/wiki/Data_scrubbing#Btrfs

BR
G.Baroncelli
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