setborder accessops. Document the new replaceattr emulop.
While here, add a paragraph explaining the purpose of each emulop (just as
done in accessops). I believe I got them right, but a review could be good.
doing copy-on-write.
- Change VFS_SNAPSHOT() to return the snapshot vnode locked.
- Make the IO path for copy-on-write and snapshot-read more lightweight.
Avoids deadlocks where vn_rdwr(...READ...) has a shared lock and needs
to copy-on-write.
Avoids deadlocks/panics where to clean pages the copy-on-write needs
to allocate pages for its VOP_PUTPAGES().
L_COWINPROGRESS part approved by: Jason R. Thorpe <thorpej@netbsd.org>
as LK_SHARED, the VOP_ code (in all our existing file systems)
was implememted assuming exclusive locking. Use of LK_SHARED
is technically a bug and only works right for uni-processor and
big-lock SMP systems. Our current file systems will blow up
(probably quite subtlely) with LK_SHARED and fine-grained SMP
locking.
- Not enabled by default. Needs kernel option FFS_SNAPSHOT.
- Change parameters of ffs_blkfree.
- Let the copy-on-write functions return an error so spec_strategy
may fail if the copy-on-write fails.
- Change genfs_*lock*() to use vp->v_vnlock instead of &vp->v_lock.
- Add flag B_METAONLY to VOP_BALLOC to return indirect block buffer.
- Add a function ffs_checkfreefile needed for snapshot creation.
- Add special handling of snapshot files:
Snapshots may not be opened for writing and the attributes are read-only.
Use the mtime as the time this snapshot was taken.
Deny mtime updates for snapshot files.
- Add function transferlockers to transfer any waiting processes from
one lock to another.
- Add vfsop VFS_SNAPSHOT to take a snapshot and make it accessible through
a vnode.
- Add snapshot support to ls, fsck_ffs and dump.
Welcome to 2.0F.
Approved by: Jason R. Thorpe <thorpej@netbsd.org>
dbj