Re: kern/50725 ffs -o discard crash/unmount safety issues

[Jaromír Doleček <jaromir.dolecek%gmail.com@localhost>]

The following reply was made to PR kern/50725; it has been noted by GNATS.

From: =?UTF-8?B?SmFyb23DrXIgRG9sZcSNZWs=?= <jaromir.dolecek%gmail.com@localhost>
To: gnats-bugs%netbsd.org@localhost
Cc: 
Subject: Re: kern/50725 ffs -o discard crash/unmount safety issues
Date: Sun, 25 Sep 2016 00:40:58 +0200

 There is another interesting thing regarding wapbl + discard, which
 needs to be taken care of.
 
 In ffs_wapbl_sync_metadata() called from wapbl_flush(), the code loops
 over deallocblks and calls ffs_blkfree(). Then it calls ffs_cgupdate()
 to save the cg descriptors to disk, which makes it in turn queued for
 journal write.
 
 However, if discard is active, those ffs_blkfree() just register the
 discard and do not modify the cg's right away. This means that cgs are
 not saved as part of the transaction in the flush, and get to saved
 only on the next sync.
 
 Jaromir