From 98257af5a2ad0c5b502ebd07094d9fd8ce87acef Mon Sep 17 00:00:00 2001 From: "J. Bruce Fields" Date: Sun, 30 Sep 2007 22:18:55 -0400 Subject: Documentation: move locks.txt in filesystems/ This documentation (about file locking) belongs in filesystems/. Signed-off-by: J. Bruce Fields --- Documentation/00-INDEX | 2 -- Documentation/filesystems/00-INDEX | 2 ++ Documentation/filesystems/locks.txt | 67 +++++++++++++++++++++++++++++++++++++ Documentation/locks.txt | 67 ------------------------------------- 4 files changed, 69 insertions(+), 69 deletions(-) create mode 100644 Documentation/filesystems/locks.txt delete mode 100644 Documentation/locks.txt diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index 910473cb1c1..cc10ce7dc33 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -230,8 +230,6 @@ local_ops.txt - semantics and behavior of local atomic operations. lockdep-design.txt - documentation on the runtime locking correctness validator. -locks.txt - - info on file locking implementations, flock() vs. fcntl(), etc. logo.gif - full colour GIF image of Linux logo (penguin - Tux). logo.txt diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX index e801076812a..599593a1706 100644 --- a/Documentation/filesystems/00-INDEX +++ b/Documentation/filesystems/00-INDEX @@ -52,6 +52,8 @@ isofs.txt - info and mount options for the ISO 9660 (CDROM) filesystem. jfs.txt - info and mount options for the JFS filesystem. +locks.txt + - info on file locking implementations, flock() vs. fcntl(), etc. mandatory-locking.txt - info on the Linux implementation of Sys V mandatory file locking. ncpfs.txt diff --git a/Documentation/filesystems/locks.txt b/Documentation/filesystems/locks.txt new file mode 100644 index 00000000000..fab857accbd --- /dev/null +++ b/Documentation/filesystems/locks.txt @@ -0,0 +1,67 @@ + File Locking Release Notes + + Andy Walker + + 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. + 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 - - 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. - -- cgit v1.2.3