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separately (nfs, cd9660 etc) or keept as a first element of structure referenced by v_data pointer(ffs). Such organization leads to known problems with stacked filesystems. From this point vop_no*lock*() functions maintain only interlock lock. vop_std*lock*() functions maintain built-in v_lock structure using lockmgr(). vop_sharedlock() is compatible with vop_stdunlock(), but maintains a shared lock on vnode. If filesystem wishes to export lockmgr compatible lock, it can put an address of this lock to v_vnlock field. This indicates that the upper filesystem can take advantage of it and use single lock structure for entire (or part) of stack of vnodes. This field shouldn't be examined or modified by VFS code except for initialization purposes. Reviewed in general by: mckusick |
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| .. | ||
| ffs_alloc.c | ||
| ffs_balloc.c | ||
| ffs_extern.h | ||
| ffs_inode.c | ||
| ffs_snapshot.c | ||
| ffs_softdep.c | ||
| ffs_softdep_stub.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