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with the new snapshot code. Update addaliasu to correctly implement the semantics of the old checkalias function. When a device vnode first comes into existence, check to see if an anonymous vnode for the same device was created at boot time by bdevvp(). If so, adopt the bdevvp vnode rather than creating a new vnode for the device. This corrects a problem which caused the kernel to panic when taking a snapshot of the root filesystem. Change the calling convention of vn_write_suspend_wait() to be the same as vn_start_write(). Split out softdep_flushworklist() from softdep_flushfiles() so that it can be used to clear the work queue when suspending filesystem operations. Access to buffers becomes recursive so that snapshots can recursively traverse their indirect blocks using ffs_copyonwrite() when checking for the need for copy on write when flushing one of their own indirect blocks. This eliminates a deadlock between the syncer daemon and a process taking a snapshot. Ensure that softdep_process_worklist() can never block because of a snapshot being taken. This eliminates a problem with buffer starvation. Cleanup change in ffs_sync() which did not synchronously wait when MNT_WAIT was specified. The result was an unclean filesystem panic when doing forcible unmount with heavy filesystem I/O in progress. Return a zero'ed block when reading a block that was not in use at the time that a snapshot was taken. Normally, these blocks should never be read. However, the readahead code will occationally read them which can cause unexpected behavior. Clean up the debugging code that ensures that no blocks be written on a filesystem while it is suspended. Snapshots must explicitly label the blocks that they are writing during the suspension so that they do not cause a `write on suspended filesystem' panic. Reorganize ffs_copyonwrite() to eliminate a deadlock and also to prevent a race condition that would permit the same block to be copied twice. This change eliminates an unexpected soft updates inconsistency in fsck caused by the double allocation. Use bqrelse rather than brelse for buffers that will be needed soon again by the snapshot code. This improves snapshot performance. |
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|---|---|---|
| .. | ||
| ffs_alloc.c | ||
| ffs_balloc.c | ||
| ffs_extern.h | ||
| ffs_inode.c | ||
| ffs_snapshot.c | ||
| ffs_softdep_stub.c | ||
| ffs_softdep.c | ||
| ffs_subr.c | ||
| ffs_tables.c | ||
| ffs_vfsops.c | ||
| ffs_vnops.c | ||
| fs.h | ||
| README.snapshot | ||
| README.softupdates | ||
| softdep.h | ||
$FreeBSD$ Using Soft Updates To enable the soft updates feature in your kernel, add option SOFTUPDATES to your kernel configuration. Once you are running a kernel with soft update support, you need to enable it for whichever filesystems you wish to run with the soft update policy. This is done with the -n option to tunefs(8) on the UNMOUNTED filesystems, e.g. from single-user mode you'd do something like: tunefs -n enable /usr To permanently enable soft updates on the /usr filesystem (or at least until a corresponding ``tunefs -n disable'' is done). Soft Updates Copyright Restrictions As of June 2000 the restrictive copyright has been removed and replaced with a `Berkeley-style' copyright. The files implementing soft updates now reside in the sys/ufs/ffs directory and are compiled into the generic kernel by default. Soft Updates Status The soft updates code has been running in production on many systems for the past two years generally quite successfully. The two current sets of shortcomings are: 1) On filesystems that are chronically full, the two minute lag from the time a file is deleted until its free space shows up will result in premature filesystem full failures. This failure mode is most evident in small filesystems such as the root. For this reason, use of soft updates is not recommended on the root filesystem. 2) If your system routines runs parallel processes each of which remove many files, the kernel memory rate limiting code may not be able to slow removal operations to a level sustainable by the disk subsystem. The result is that the kernel runs out of memory and hangs. Both of these problems are being addressed, but have not yet been resolved. There are no other known problems at this time. How Soft Updates Work For more general information on soft updates, please see: http://www.mckusick.com/softdep/ http://www.ece.cmu.edu/~ganger/papers/CSE-TR-254-95/ -- Marshall Kirk McKusick <mckusick@mckusick.com> July 2000