Only after the journal transaction has been committed in this fashion can the kernel do the real metadata writes at its leisure; should the system crash in the middle, the information needed to safely finish the job can be found in the journal. There will be no filesystem corruption caused by a partial metadata update.
This comes from https://lwn.net/Articles/283161 .
What's the usage of should in the highlighted sentence?
should the system crash in the middle, How should I interpret it?
You can read "should the system crash in the middle, the information...can be found in the journal" as a conditional that would more commonly be expressed as:
If the system should crash in the middle, the information...can be found in the journal,
Swan in Practical English Usage (p237) says this about conditionals with should:
We can suggest that something is unlikely, or not particularly probable, by using should in the if-clause.
In a later section called leaving out if: formal inversion structures (p238), Swan states:
In formal and literary styles, if can be dropped and an auxiliary verb put before the subject. This happens mostly with were, had and should.
He gives this example:
Should you change your mind... (=If you should change your mind...)
