[PATCH/RFC] Lustre VFS patch

["Peter J. Braam" <braam@clusterfs.com>]

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Hi Linus, Andrew & others,

Many people have asked me to have this patched reviewed, and
considered for inclusion in 2.6 after some reworking.  At the kernel
summit last summer we discussed these issues.

This patch is not the Lustre file system, with client file system,
Lustre RPC, server code etc.  This patch would enable people to run
Lustre with modules loading into unmodified kernels and this appears
to be something vendors really would like to see.  FYI, at the moment
Lustre is a just a little bit larger than NFS, comparing clients,
servers, and rpc code for each (60K vs 80K lines of code).

This patch was written quite defensively: file systems not using 
intents should really be completely unaffected.

I attach a little tar ball with patches and a series file which
describes the order of the patches.  Below is a short description of
each of the patches.  I also want to tell you a few things we have 
worked on that are not present in this patch:
 
 - deal with "pinning" directories that are CWD or mount points.  They
   should not be removable/unlinkable by remote nodes, and the FS needs
   some indication of that.

 - in Lustre d_parent is not necessarily valid, so sys_getcwd needs to
   be careful.  In Ottawa we discussed adding an optional hook.

 - changes to NFSD to allow it to run on top of Lustre

 - per file system locking operations (refinining i_sem) to allow 
   parallel updates in one directory. 

It goes without saying that many people in CFS have made contributions
to this patch and that the ideas were heavily influenced by discussions
with the kernel community.

Please give me your thoughts about how we can move forward with this.
 
Regards,

- Peter -
 
 
dev_read_only-vanilla-2.6.patch
 
  This introduces an ioctl on block devices to stop doing I/O. The
  only purpose of the patch is automated recovery regression testing,
  it is very convenient to have this available.

export-vanilla-2.6.patch
 
  Export symbols used by Lustre.

header_guards-vanilla-2.6.patch
 
  Small bug fix to avoid double inclusion of headers

lustre_version.patch
 
  A tiny header to check that the kernel patch and Lustre modules are
  compatible.
  
vfs-dcache_locking-vanilla-2.6.patch

  A trivial patch to make functions available to lustre that do
  d_move, d_rehash, without taking/dropping the dcache lock.
 
vfs-dcache_lustre_invalid-vanilla-2.6.patch
 
  This allows dentries to be d_invalidate'd if a bit is set in the
  FLAGS.  This is required when dentries that are busy on the local
  node are invalidated on another client system.

vfs-intent_api-vanilla-2.6.patch
 
  Introduce intents for other operations.  Add a file system hook to
  release intent data.  Make a few "intent versions" of functions such
  as "lookup_one_len_it" and "user_walk_it" available through headers.
  Arrange that the open intent is visible in the open methods. Add a
  few missing intent_init calls.

vfs-intent_exec-vanilla-2.6.patch
 
  Add intents for open in the context of execution.
 
vfs-intent_init-vanilla-2.6.patch
 
  Add intent_init for all operations, not just for open.

vfs-intent_lustre-vanilla-2.6.patch
 
  Add a pointer to per fs intent_data structure to the struct lookup_intent.
 
vfs-raw_ops-vanilla-2.6.patch

  This adds raw operations for setattr, mkdir, rmdir, mknod, unlink,
  symlink, link and rename.  The raw operations look up the parent
  directories (but not leaf nodes) involved in the operation and then
  ask the file system to execute the operation.  These methods allow
  us to delegate the execution of these functions to the server, and
  instantiate no dentries for leaf nodes, leaf nodes will only enter
  the dcache on subsequent lookups.  This patch dramatically
  simplifies the client/server lock management, particularly for
  rename.
 
  In Ottawa Linus suggested that we could maybe do this with intents
  instead.  I feel that both are ugly, both are possible but intents
  looked akward.
 
vfs-revalidate_counter-vanilla-2.6.patch
 
  We found that dentries could be invalidated multiple times through
  activity on remote nodes, but this shoudl not lead to failure in
  Lustre.  The revalidation path real_lookup was adapted to take a few
  more iterations through the revalidation before giving up.  This
  revalidation takes the form of first revalidating, then looking up
  if it fails, and possibly revalidating a few more times (see above)
  until there is success.
 
vfs-revalidate_special-vanilla-2.6.patch

 
  We add nameidata flags to indicate that a link sits in the middle of
  the path and a flag that inidicates we are looking at the last
  component of a path.  [If someone knows if the existing flags could
  detect this, that would be welcome.]  To pass intents when the last
  pathname component is a "." we insert a "special" revalidation
  function that calls revalidate dentry when such a pathname is
  traversed.
 
vfs_intent-flags_rename-vanilla-2.6.patch
 
  As Linus requested in Ottawa last summer, rename intent.open.flags
  to intent.  it_flags and intent.open.create_mode to
  intent.it_create_mode.  Remove the union of "intents", which only
  contained an open_intent, and replace it with a single struct
  lookup_intent included in the nameidata.
 
vfs-do_truncate.patch
  
  We added a parameter to do_truncate so that the FS can now if it is
  being called from open or not.


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