Import of Linux/MIPS 2.1.14

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+		      File Locking Release Notes
+
+		Andy Walker <andy@lysaker.kvaerner.no>
+
+			    21 Sep 1996
+
+
+1. What's New?
+--------------
+
+1.1 Flock Emulation Warnings
+----------------------------
+Many people will have noticed the ugly messages that the file locking
+code started generating with the release of kernel version 1.3.95. The
+messages look something like this:
+
+    fcntl_setlk() called by process XX with broken flock() emulation
+
+This is a warning for people using older C libraries that those libraries
+are still calling the pre 1.3.x flock() emulation routines, instead of
+the real flock() system call. The old routines are quite badly broken,
+especially with respect to parent-child lock sharing, and can give bad
+results if, for example, sendmail attempts to use them.
+
+Fixed versions of the C libraries have been on public release for many
+months. The latest versions at the time of writing are 5.3.12 (released)
+or 5.4.6 (testing) for ELF. There is also a 4.7.6 release for people
+using a.out systems.
+
+With the release of Linux 2.0 Linus decided to be lenient on the
+stragglers and changed the warning message so that the kernel will only
+complain once and then shut up. That should make life more bearable even
+for people who, for some reason, don't want to upgrade their libraries.
+
+
+1.2 Disallow Mixed Locks
+------------------------
+
+1.2.1 Sendmail Problems
+---------------------
+Because sendmail was unable to use the old flock() emulation, many sendmail
+installations use fcntl() instead of flock(). This is true of Slackware 3.0
+for example. This gave rise to some other subtle problems if sendmail was
+configured to rebuild the alias file. Sendmail tried to lock the aliases.dir
+file with fcntl() at the same time as the GDBM routines tried to lock this
+file with flock(). With pre 1.3.96 kernels this could result in deadlocks that,
+over time, or under a very heavy mail load, would eventually cause the kernel
+to lock solid with deadlocked processes.
+
+
+1.2.2 The Solution
+------------------
+I have chosen the rather cruel solution of disallowing mixed locking styles
+on a given file at a given time. Attempts to lock a file with flock() when
+fcntl() locks exist, or vice versa, return with an error status of EBUSY.
+This seemed to be the only way to avoid all possible deadlock conditions,
+as flock() locks do not strictly have one owner process and so can't be
+checked for deadlocking in the usual manner.
+
+The process that created a lock with flock() might have forked multiple
+children and exited. Previously the parent process would have been marked
+as the owner of the lock, but deadlocks could just have easily occurred in
+one or more of the children, which we would not have been able to identify
+and avoid.
+
+Some programs may break (again, groan). In particular the aforementioned
+sendmail may have problems running in 'newaliases' mode. It will no longer
+deadlock though. Recompile sendmail to use flock() and your troubles will
+be over.
+
+1.3 Mandatory Locking As A Mount Option
+---------------------------------------
+
+Mandatory locking, as described in 'Documentation/mandatory.txt' was prior
+to this release a general configuration option that was valid for all
+mounted filesystems. This had a number of inherent dangers, not the least
+of which was the ability to freeze an NFS server by asking it to read a
+file for which a mandatory lock existed.
+
+From this release of the kernel, mandatory locking can be turned on and off
+on a per-filesystem basis, using the mount options 'mand' and 'nomand'.
+The default is to disallow mandatory locking. The intention is that
+mandatory locking only be enabled on a local filesystem as the specific need
+arises.
+
+Until an updated version of mount(8) becomes available you may have to apply
+this patch to the mount sources (based on the version distributed with Rick
+Faiths util-linux-2.5 package):
+
+*** mount.c.orig	Sat Jun  8 09:14:31 1996
+--- mount.c	Sat Jun  8 09:13:02 1996
+***************
+*** 100,105 ****
+--- 100,107 ----
+    { "noauto",	0, MS_NOAUTO	},	/* Can  only be mounted explicitly */
+    { "user",	0, MS_USER	},	/* Allow ordinary user to mount */
+    { "nouser",	1, MS_USER	},	/* Forbid ordinary user to mount */
++   { "mand",	0, MS_MANDLOCK	},	/* Allow mandatory locks on this FS */
++   { "nomand",	1, MS_MANDLOCK	},	/* Forbid mandatory locks on this FS */
+    /* add new options here */
+  #ifdef MS_NOSUB
+    { "sub",	1, MS_NOSUB	},	/* allow submounts */