# $NetBSD: CHANGES,v 1.5 2005/12/11 12:25:26 christos Exp $ kernel: - Instead of blindly continuing when it encounters an Inode that is locked by another process, lfs_markv will process the rest of the inodes passed to it and then return EAGAIN. The cleaner will recognize this and not mark the segment clean. When the cleaner runs again, the segment containg the (formerly) locked inode will sort high for cleaning, since it is now almost entirely empty. - A beginning has been made to test keeping atime information in the Ifile, instead of on the inodes. This should make read-mostly filesystems significantly faster, since the inodes will then remain close to the data blocks on disk; but of course the ifile will be somewhat larger. This code is not enabled, as it makes the format of IFILEs change. - The superblock has been broken into two components: an on-disk superblock using fixed-size types, exactly 512 bytes regardless of architecture (or could be enlarged in multiples of the media block size up to LFS_SBPAD); and an in-memory superblock containing the information only useful to a running LFS, including segment pointers, etc. The superblock checksumming code has been modified to make future changes to the superblock format easier. - Because of the way that lfs_writeseg works, buffers are freed before they are really written to disk: their contents are copied into large buffers which are written async. Because the buffer cache does not serve to throttle these writes, and malloced memory is used to hold them, there is a danger of running out of kmem_map. To avoid this, a new compile-time parameter, LFS_THROTTLE, is used as an upper bound for the number of partial-segments allowed to be in progress writing at any given time. - If the system crashes between the point that a checkpoint is scheduled for writing and the time that the write completes, the filesystem could be left in an inconsistent state (no valid checkpoints on disk). To avoid this, we toggle between the first two superblocks when checkpointing, and (if it is indicated that no roll-forward agent exists) do not allow one checkpoint to occur before the last one has completed. When the filesystem is mounted, it uses the *older* of the first two superblocks. - DIROPs: The design of the LFS includes segregating vnodes used in directory operations, so that they can be written at the same time during a checkpoint, avoiding filesystem inconsistency after a crash. Code for this was partially written for BSD4.4, but was not complete or enabled. In particular, vnodes marked VDIROP could be flushed by getnewvnode at any time, negating the usefulness of marking a vnode VDIROP, since if the filesystem then crashed it would be inconsistent. Now, when a vnode is first marked VDIROP it is also referenced. To avoid running out of vnodes, an attempt to mark more than LFS_MAXDIROP vnodes wth VDIROP will sleep, and trigger a partial-segment write when no dirops are active. - LFS maintains a linked list of free inode numbers in the Ifile; accesses to this list are now protected by a simple lock. - lfs_vfree is not allowed to run while an inode has blocks scheduled for writing, since that could trigger a miscounting in lfs_truncate. - lfs_balloc now correctly extends fragments, if a block is written beyond the current end-of-file. - Blocks which have already been gathered into a partial-segment are not allowed to be extended, since if they were, any blocks following them would either be written in the wrong place, or overwrite other blocks. - The LFS buffer-header accounting, which triggers a partial-segment write if too many buffer-headers are in use by the LFS subystem, has been expanded to include *bytes* used in LFS buffers as well. - Reads of the Ifile, which almost always come from the cleaner, can no longer trigger a partial-segment write, since this could cause a deadlock. - Support has been added (but not tested, and currently disabled by default) for true read-only filesystems. Currently, if a filesystem is mounted read-only the cleaner can still operate on it, but this obviously would not be true for read-only media. (I think the original plan was for the roll-forward agent to operate using this "feature"?) - If a fake buffer is created by lfs_markv and another process draws the same block in and changes it, the fake buffer is now discarded and replaced by the "real" buffer containing the new data. - An inode which has blocks gathered no longer has IN_MODIFIED set, but still does in fact have dirty blocks attached. lfs_update will now wait for such an inode's writes to complete before it runs, suppressing a panic in vinvalbuf. - Many filesystem operations now update the Ifile's mtime, allowing the cleaner to detect when the filesystem is idle, and clean more vigorously during such times (cf. Blackwell et al., 1995). - When writing a partial-segment, make sure that the current segment is still marked ACTIVE afterward (otherwise the cleaner might try to clean it, since it might well be mostly empty). - Don't trust the cleaner so much. Sort the blocks during gathering, even if they came from the cleaner; verify the location of on-disk inodes, even if the cleaner says it knows where they came from. - The cleaning code (lfs_markv in particular) has been entirely rewritten, and the partial-segment writing code changed to match. Lfs_markv no longer uses its own implementation of lfs_segwrite, but marks inodes with IN_CLEANING to differentiate them from the non-cleaning inodes. This change fixes numerous problems with the old cleaner, including a buffer overrun, and lost extensions in active fragments. lfs_bmapv looks up and returns the addresses of inode blocks, so the cleaner can do something intelligent with them. If IN_CLEANING is set on an inode during partial-segment write, only fake buffers will be written, and IN_MODIFIED will not be cleared, saving us from a panic in vinvalbuf. The addition of IN_CLEANING also allows dirops to be active while cleaning is in progress; since otherwise buffers engaged in active dirops might be written ahead of schedule, and cause an inconsistent checkpoint to be written to disk. (XXX - even now, DIROP blocks can sometimes be written to disk, if we are cleaning the same blocks as are active? Grr, I don't see a good solution for this!) - Added sysctl entries for LFS. In particular, `writeindir' controls whether indirect blocks are written during non-checkpoint writes. (Since there is no roll-forward agent as yet, there is no penalty in not writing indirect blocks.) - Wake up the cleaner at fs-unmount time, so it can die (if we unmount and then remount, we could conceivably get more than one cleaner operating at once). newfs_lfs: - The ifile inode is now created with the schg flag set, since nothing ever modifies it. This could be a pain for the roll-forward agent, but since that should really run *before* the filesystem is mounted, I don't care. - For large disks, it may be necessary to write one or more indirect blocks when the ifile inode is created. Newlfs has been changed to write the first indirect block, if necessary. It should instead just build a set of inodes and blocks, and then use the partial-segment writing routine mentioned above to write an ifile of whatever size is desired. lfs_cleanerd: - Now writes information to the syslog. - Can now deal properly with fragments. - Sometimes, the cleaner can die. (Why?) If this happens and we don't notice, we're screwed, since the fs will overfill. So, the invoked cleaner now spawns itself repeatedly, a la init(8), to ensure that a cleaner is always present to clean the fs. - Added a flag to clean more actively, not on low load average but filesystem inactivity; a la Blackwell et al., 1995. fsck_lfs: - Exists, although it currently cannot actually fix anything (it is a diagnostic tool only at this point).