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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /Documentation/filesystems/dlmfs.rst | |
parent | Initial commit. (diff) | |
download | linux-upstream/5.10.209.tar.xz linux-upstream/5.10.209.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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-rw-r--r-- | Documentation/filesystems/dlmfs.rst | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/Documentation/filesystems/dlmfs.rst b/Documentation/filesystems/dlmfs.rst new file mode 100644 index 000000000..28dd41a63 --- /dev/null +++ b/Documentation/filesystems/dlmfs.rst @@ -0,0 +1,140 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. include:: <isonum.txt> + +===== +DLMFS +===== + +A minimal DLM userspace interface implemented via a virtual file +system. + +dlmfs is built with OCFS2 as it requires most of its infrastructure. + +:Project web page: http://ocfs2.wiki.kernel.org +:Tools web page: https://github.com/markfasheh/ocfs2-tools +:OCFS2 mailing lists: https://oss.oracle.com/projects/ocfs2/mailman/ + +All code copyright 2005 Oracle except when otherwise noted. + +Credits +======= + +Some code taken from ramfs which is Copyright |copy| 2000 Linus Torvalds +and Transmeta Corp. + +Mark Fasheh <mark.fasheh@oracle.com> + +Caveats +======= +- Right now it only works with the OCFS2 DLM, though support for other + DLM implementations should not be a major issue. + +Mount options +============= +None + +Usage +===== + +If you're just interested in OCFS2, then please see ocfs2.txt. The +rest of this document will be geared towards those who want to use +dlmfs for easy to setup and easy to use clustered locking in +userspace. + +Setup +===== + +dlmfs requires that the OCFS2 cluster infrastructure be in +place. Please download ocfs2-tools from the above url and configure a +cluster. + +You'll want to start heartbeating on a volume which all the nodes in +your lockspace can access. The easiest way to do this is via +ocfs2_hb_ctl (distributed with ocfs2-tools). Right now it requires +that an OCFS2 file system be in place so that it can automatically +find its heartbeat area, though it will eventually support heartbeat +against raw disks. + +Please see the ocfs2_hb_ctl and mkfs.ocfs2 manual pages distributed +with ocfs2-tools. + +Once you're heartbeating, DLM lock 'domains' can be easily created / +destroyed and locks within them accessed. + +Locking +======= + +Users may access dlmfs via standard file system calls, or they can use +'libo2dlm' (distributed with ocfs2-tools) which abstracts the file +system calls and presents a more traditional locking api. + +dlmfs handles lock caching automatically for the user, so a lock +request for an already acquired lock will not generate another DLM +call. Userspace programs are assumed to handle their own local +locking. + +Two levels of locks are supported - Shared Read, and Exclusive. +Also supported is a Trylock operation. + +For information on the libo2dlm interface, please see o2dlm.h, +distributed with ocfs2-tools. + +Lock value blocks can be read and written to a resource via read(2) +and write(2) against the fd obtained via your open(2) call. The +maximum currently supported LVB length is 64 bytes (though that is an +OCFS2 DLM limitation). Through this mechanism, users of dlmfs can share +small amounts of data amongst their nodes. + +mkdir(2) signals dlmfs to join a domain (which will have the same name +as the resulting directory) + +rmdir(2) signals dlmfs to leave the domain + +Locks for a given domain are represented by regular inodes inside the +domain directory. Locking against them is done via the open(2) system +call. + +The open(2) call will not return until your lock has been granted or +an error has occurred, unless it has been instructed to do a trylock +operation. If the lock succeeds, you'll get an fd. + +open(2) with O_CREAT to ensure the resource inode is created - dlmfs does +not automatically create inodes for existing lock resources. + +============ =========================== +Open Flag Lock Request Type +============ =========================== +O_RDONLY Shared Read +O_RDWR Exclusive +============ =========================== + + +============ =========================== +Open Flag Resulting Locking Behavior +============ =========================== +O_NONBLOCK Trylock operation +============ =========================== + +You must provide exactly one of O_RDONLY or O_RDWR. + +If O_NONBLOCK is also provided and the trylock operation was valid but +could not lock the resource then open(2) will return ETXTBUSY. + +close(2) drops the lock associated with your fd. + +Modes passed to mkdir(2) or open(2) are adhered to locally. Chown is +supported locally as well. This means you can use them to restrict +access to the resources via dlmfs on your local node only. + +The resource LVB may be read from the fd in either Shared Read or +Exclusive modes via the read(2) system call. It can be written via +write(2) only when open in Exclusive mode. + +Once written, an LVB will be visible to other nodes who obtain Read +Only or higher level locks on the resource. + +See Also +======== +http://opendlm.sourceforge.net/cvsmirror/opendlm/docs/dlmbook_final.pdf + +For more information on the VMS distributed locking API. |