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kern/45676: ffs/wapbl problems
>Synopsis: ffs/wapbl problems
>Arrival-Date: Fri Dec 02 12:15:00 +0000 2011
>Originator: YAMAMOTO Takashi
>Release: NetBSD current
1. ffs_full_fsync has code to skip wapbl_flush if vp->v_dirtyblkhd is
empty. i don't think it's a safe optimization because the buffer
which contains dinode would hang on devvp, not this vp. probably
another per-vnode/inode field is necessary to remember if the log is
involved for the file.
2. ffs_full_fsync and ffs_fsync skip wapbl_flush for FSYNC_DATAONLY.
it seems wrong because block pointers should be written out.
3. ffs_full_fsync and ffs_fsync does not obey FSYNC_CACHE when wapbl
is used but wapbl_flush is not necessary.
4. ffs_full_fsync and ffs_fsync should be merged as now softdep has
5. wapbl_flush issues two DIOCCACHESYNC calls which are typically
very expensive. while i'm not sure why _only_ this part of code
needs this level of guarantee, at least it should be reduced to
a single call, probably using a checksum as the comment in
6. wapbl should have underlying device requirements documented
somewhere. (torn writes, disk cache behaviour, etc)
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