Prev: [PATCH 11/11] ocfs2_dlmfs: Enable the use of user cluster stacks.
Next: [PATCH 4/4] drivers: dream: Code style fix
From: Joel Becker on 10 Feb 2010 04:40
Changes from v1:
- Ignore truncation of dlmfs files. The LVB is a constant size.
- Check the LVB for validity before copying it to userspace. LVBs can
become invalid during lock recovery.
- This has now been tested to pass lvb_torture on two nodes with fsdlm

ocfs2 ships with its own cluster stack, o2cb. The dlm portion, o2dlm,
is accessible to userspace via a custom filesystem, ocfs2_dlmfs. Files
in this filesytem represent cluster lock resources. Open the file, and
you take the lock. The libo2dlm library wraps this filesystem,
providing a very simplified cluster locking API to userspace programs.

One of the things left out of the simplified interface is the ability to
learn that other nodes want a lock. Notification that another node
wants the lock is called a "blocking asynchronous system trap", or
"bast". Kernel users of o2dlm can register basts as they please, but
programs using libo2dlm and ocfs2_dlmfs cannot. Thus, they must not
hold a lock forever; other nodes will never get the lock.

The first improvement in this series adds poll(2) support to
ocfs2_dlmfs. POLLIN on an open ocfs2_dlmfs flie signals a bast. Now
user programs can hold a lock until they are notified to release it.

Another limitation of ocfs2_dlmfs is its reliance on o2dlm and thus the
entire o2cb cluster stack. The ocfs2 filesystem has a glue layer,
called "stackglue", that allows it to switch between o2cb+o2dlm and the
userspace cluster stacks that work with fs/dlm. This means userspace
programs for ocfs2 have to know about libo2dlm when o2dlm is employed
and libdlm when fs/dlm is employed.

The second improvement is to make ocfs2_dlmfs use stackglue. Instead of
directly calling o2dlm APIs, it uses stackglue to remain agnostic of the
cluster stack. Now a system using a userspace cluster stack and fs/dlm
can mount ocfs2_dlmfs and use libo2dlm. This benefits everyone.

Joel

[Pull]
git://git.kernel.org/pub/scm/linux/kernel/git/jlbec/ocfs2.git dlmfs-stackglue
[View]
http://git.kernel.org/?p=linux/kernel/git/jlbec/ocfs2.git;a=shortlog;h=refs/heads/dlmfs-stackglue

fs/ocfs2/Makefile | 1 +
fs/ocfs2/dlm/Makefile | 3 +-
fs/ocfs2/dlmfs/Makefile | 5 +
fs/ocfs2/{dlm => dlmfs}/dlmfs.c | 127 +++++++++++++-----
fs/ocfs2/{dlm => dlmfs}/dlmfsver.c | 0
fs/ocfs2/{dlm => dlmfs}/dlmfsver.h | 0
fs/ocfs2/{dlm => dlmfs}/userdlm.c | 266 ++++++++++++++++++------------------
fs/ocfs2/{dlm => dlmfs}/userdlm.h | 16 +-
fs/ocfs2/dlmglue.c | 198 +++++++++++++--------------
fs/ocfs2/ocfs2.h | 2 +-
fs/ocfs2/ocfs2_lockingver.h | 2 +
fs/ocfs2/stack_o2cb.c | 37 +++---
fs/ocfs2/stack_user.c | 49 +++----
fs/ocfs2/stackglue.c | 98 +++++++++-----
fs/ocfs2/stackglue.h | 95 ++++++++------
15 files changed, 502 insertions(+), 397 deletions(-)



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