Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  3) ==========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  4) File Locking Release Notes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  5) ==========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  6) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  7) 		Andy Walker <andy@lysaker.kvaerner.no>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  8) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  9) 			    12 May 1997
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) 1. What's New?
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) 1.1 Broken Flock Emulation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) --------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) The old flock(2) emulation in the kernel was swapped for proper BSD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) compatible flock(2) support in the 1.3.x series of kernels. With the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) release of the 2.1.x kernel series, support for the old emulation has
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) been totally removed, so that we don't need to carry this baggage
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) forever.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) This should not cause problems for anybody, since everybody using a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) 2.1.x kernel should have updated their C library to a suitable version
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) anyway (see the file "Documentation/process/changes.rst".)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) 1.2 Allow Mixed Locks Again
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) 1.2.1 Typical Problems - Sendmail
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) Because sendmail was unable to use the old flock() emulation, many sendmail
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) installations use fcntl() instead of flock(). This is true of Slackware 3.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) for example. This gave rise to some other subtle problems if sendmail was
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) configured to rebuild the alias file. Sendmail tried to lock the aliases.dir
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) file with fcntl() at the same time as the GDBM routines tried to lock this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) file with flock(). With pre 1.3.96 kernels this could result in deadlocks that,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) over time, or under a very heavy mail load, would eventually cause the kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) to lock solid with deadlocked processes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) 1.2.2 The Solution
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) ^^^^^^^^^^^^^^^^^^
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) The solution I have chosen, after much experimentation and discussion,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) is to make flock() and fcntl() locks oblivious to each other. Both can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) exists, and neither will have any effect on the other.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) I wanted the two lock styles to be cooperative, but there were so many
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) race and deadlock conditions that the current solution was the only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) practical one. It puts us in the same position as, for example, SunOS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) 4.1.x and several other commercial Unices. The only OS's that support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) cooperative flock()/fcntl() are those that emulate flock() using
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) fcntl(), with all the problems that implies.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) 1.3 Mandatory Locking As A Mount Option
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) ---------------------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) Mandatory locking, as described in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) 'Documentation/filesystems/mandatory-locking.rst' was prior to this release a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) general configuration option that was valid for all mounted filesystems.  This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) had a number of inherent dangers, not the least of which was the ability to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) freeze an NFS server by asking it to read a file for which a mandatory lock
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) existed.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) From this release of the kernel, mandatory locking can be turned on and off
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) on a per-filesystem basis, using the mount options 'mand' and 'nomand'.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) The default is to disallow mandatory locking. The intention is that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) mandatory locking only be enabled on a local filesystem as the specific need
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) arises.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72)