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| author | J. Bruce Fields <bfields@citi.umich.edu> | 2007-09-30 22:18:55 -0400 |
|---|---|---|
| committer | J. Bruce Fields <bfields@citi.umich.edu> | 2007-10-09 18:32:45 -0400 |
| commit | 98257af5a2ad0c5b502ebd07094d9fd8ce87acef (patch) | |
| tree | c8ae7b8517ad2f2d6e1cad13b9f15d6b2ebb4e64 /Documentation/locks.txt | |
| parent | 9efa68ed079af97f4e9477eadef567ffe64f7afc (diff) | |
Documentation: move locks.txt in filesystems/
This documentation (about file locking) belongs in filesystems/.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Diffstat (limited to 'Documentation/locks.txt')
| -rw-r--r-- | Documentation/locks.txt | 67 |
1 files changed, 0 insertions, 67 deletions
diff --git a/Documentation/locks.txt b/Documentation/locks.txt deleted file mode 100644 index fab857accbd..00000000000 --- a/Documentation/locks.txt +++ /dev/null @@ -1,67 +0,0 @@ - File Locking Release Notes - - Andy Walker <andy@lysaker.kvaerner.no> - - 12 May 1997 - - -1. What's New? --------------- - -1.1 Broken Flock Emulation --------------------------- - -The old flock(2) emulation in the kernel was swapped for proper BSD -compatible flock(2) support in the 1.3.x series of kernels. With the -release of the 2.1.x kernel series, support for the old emulation has -been totally removed, so that we don't need to carry this baggage -forever. - -This should not cause problems for anybody, since everybody using a -2.1.x kernel should have updated their C library to a suitable version -anyway (see the file "Documentation/Changes".) - -1.2 Allow Mixed Locks Again ---------------------------- - -1.2.1 Typical Problems - Sendmail ---------------------------------- -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 ------------------- -The solution I have chosen, after much experimentation and discussion, -is to make flock() and fcntl() locks oblivious to each other. Both can -exists, and neither will have any effect on the other. - -I wanted the two lock styles to be cooperative, but there were so many -race and deadlock conditions that the current solution was the only -practical one. It puts us in the same position as, for example, SunOS -4.1.x and several other commercial Unices. The only OS's that support -cooperative flock()/fcntl() are those that emulate flock() using -fcntl(), with all the problems that implies. - - -1.3 Mandatory Locking As A Mount Option ---------------------------------------- - -Mandatory locking, as described in 'Documentation/filesystems/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. - |