diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/00-INDEX | 6 | ||||
| -rw-r--r-- | Documentation/filesystems/00-INDEX | 4 | ||||
| -rw-r--r-- | Documentation/filesystems/locks.txt (renamed from Documentation/locks.txt) | 10 | ||||
| -rw-r--r-- | Documentation/filesystems/mandatory-locking.txt (renamed from Documentation/mandatory.txt) | 21 |
4 files changed, 30 insertions, 11 deletions
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX index 43e89b1537d9..cc10ce7dc339 100644 --- a/Documentation/00-INDEX +++ b/Documentation/00-INDEX @@ -145,7 +145,7 @@ fb/ feature-removal-schedule.txt - list of files and features that are going to be removed. filesystems/ - - directory with info on the various filesystems that Linux supports. + - info on the vfs and the various filesystems that Linux supports. firmware_class/ - request_firmware() hotplug interface info. floppy.txt @@ -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 @@ -240,8 +238,6 @@ m68k/ - directory with info about Linux on Motorola 68k architecture. magic-number.txt - list of magic numbers used to mark/protect kernel data structures. -mandatory.txt - - info on the Linux implementation of Sys V mandatory file locking. mca.txt - info on supporting Micro Channel Architecture (e.g. PS/2) systems. md.txt diff --git a/Documentation/filesystems/00-INDEX b/Documentation/filesystems/00-INDEX index 59db1bca7027..599593a17067 100644 --- a/Documentation/filesystems/00-INDEX +++ b/Documentation/filesystems/00-INDEX @@ -52,6 +52,10 @@ 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 - info on Novell Netware(tm) filesystem using NCP protocol. ntfs.txt diff --git a/Documentation/locks.txt b/Documentation/filesystems/locks.txt index e3b402ef33bd..fab857accbd6 100644 --- a/Documentation/locks.txt +++ b/Documentation/filesystems/locks.txt @@ -53,11 +53,11 @@ fcntl(), with all the problems that implies. 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. +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'. diff --git a/Documentation/mandatory.txt b/Documentation/filesystems/mandatory-locking.txt index bc449d49eee5..0979d1d2ca8b 100644 --- a/Documentation/mandatory.txt +++ b/Documentation/filesystems/mandatory-locking.txt @@ -3,7 +3,26 @@ Andy Walker <andy@lysaker.kvaerner.no> 15 April 1996 - + (Updated September 2007) + +0. Why you should avoid mandatory locking +----------------------------------------- + +The Linux implementation is prey to a number of difficult-to-fix race +conditions which in practice make it not dependable: + + - The write system call checks for a mandatory lock only once + at its start. It is therefore possible for a lock request to + be granted after this check but before the data is modified. + A process may then see file data change even while a mandatory + lock was held. + - Similarly, an exclusive lock may be granted on a file after + the kernel has decided to proceed with a read, but before the + read has actually completed, and the reading process may see + the file data in a state which should not have been visible + to it. + - Similar races make the claimed mutual exclusion between lock + and mmap similarly unreliable. 1. What is mandatory locking? ------------------------------ |