WSL2-Linux-Kernel/Documentation/filesystems/orangefs.txt

ORANGEFS
========

OrangeFS is an LGPL userspace scale-out parallel storage system. It is ideal
for large storage problems faced by HPC, BigData, Streaming Video,
Genomics, Bioinformatics.

Orangefs, originally called PVFS, was first developed in 1993 by
Walt Ligon and Eric Blumer as a parallel file system for Parallel
Virtual Machine (PVM) as part of a NASA grant to study the I/O patterns
of parallel programs.

Orangefs features include:

  * Distributes file data among multiple file servers
  * Supports simultaneous access by multiple clients
  * Stores file data and metadata on servers using local file system
    and access methods
  * Userspace implementation is easy to install and maintain
  * Direct MPI support
  * Stateless


MAILING LIST
============

http://beowulf-underground.org/mailman/listinfo/pvfs2-users


DOCUMENTATION
=============

http://www.orangefs.org/documentation/


USERSPACE FILESYSTEM SOURCE
===========================

http://www.orangefs.org/download

Orangefs versions prior to 2.9.3 would not be compatible with the
upstream version of the kernel client.


BUILDING THE USERSPACE FILESYSTEM ON A SINGLE SERVER
====================================================

When Orangefs is upstream, "--with-kernel" shouldn't be needed, but
until then the path to where the kernel with the Orangefs kernel client
patch was built is needed to ensure that pvfs2-client-core (the bridge
between kernel space and user space) will build properly. You can omit
--prefix if you don't care that things are sprinkled around in
/usr/local.

./configure --prefix=/opt/ofs --with-kernel=/path/to/orangefs/kernel

make

make install

Create an orangefs config file:
/opt/ofs/bin/pvfs2-genconfig /etc/pvfs2.conf

  for "Enter hostnames", use the hostname, don't let it default to
  localhost.

create a pvfs2tab file in /etc:
cat /etc/pvfs2tab
tcp://myhostname:3334/orangefs /mymountpoint pvfs2 defaults,noauto 0 0

create the mount point you specified in the tab file if needed:
mkdir /mymountpoint

bootstrap the server:
/opt/ofs/sbin/pvfs2-server /etc/pvfs2.conf -f

start the server:
/opt/osf/sbin/pvfs2-server /etc/pvfs2.conf

Now the server is running. At this point you might like to
prove things are working with:

/opt/osf/bin/pvfs2-ls /mymountpoint

You might not want to enforce selinux, it doesn't seem to matter by
linux 3.11...

If stuff seems to be working, turn on the client core:
/opt/osf/sbin/pvfs2-client -p /opt/osf/sbin/pvfs2-client-core

Mount your filesystem.
mount -t pvfs2 tcp://myhostname:3334/orangefs /mymountpoint


OPTIONS
=======

The following mount options are accepted:

  acl
    Allow the use of Access Control Lists on files and directories.

  intr
    Some operations between the kernel client and the user space
    filesystem can be interruptible, such as changes in debug levels
    and the setting of tunable parameters.

  local_lock
    Enable posix locking from the perspective of "this" kernel. The
    default file_operations lock action is to return ENOSYS. Posix
    locking kicks in if the filesystem is mounted with -o local_lock.
    Distributed locking is being worked on for the future.


DEBUGGING
=========

If you want the debug (GOSSIP) statements in a particular
source file (inode.c for example) go to syslog:

  echo inode > /sys/kernel/debug/orangefs/kernel-debug

No debugging (the default):

  echo none > /sys/kernel/debug/orangefs/kernel-debug

Debugging from several source files:

  echo inode,dir > /sys/kernel/debug/orangefs/kernel-debug

All debugging:

  echo all > /sys/kernel/debug/orangefs/kernel-debug

Get a list of all debugging keywords:

  cat /sys/kernel/debug/orangefs/debug-help


PROTOCOL BETWEEN KERNEL MODULE AND USERSPACE
============================================

Orangefs is a user space filesystem and an associated kernel module.
We'll just refer to the user space part of Orangefs as "userspace"
from here on out. Orangefs descends from PVFS, and userspace code
still uses PVFS for function and variable names. Userspace typedefs
many of the important structures. Function and variable names in
the kernel module have been transitioned to "orangefs", and The Linux
Coding Style avoids typedefs, so kernel module structures that
correspond to userspace structures are not typedefed.

The kernel module implements a pseudo device that userspace
can read from and write to. Userspace can also manipulate the
kernel module through the pseudo device with ioctl.

THE BUFMAP:

At startup userspace allocates two page-size-aligned (posix_memalign)
mlocked memory buffers, one is used for IO and one is used for readdir
operations. The IO buffer is 41943040 bytes and the readdir buffer is
4194304 bytes. Each buffer contains logical chunks, or partitions, and
a pointer to each buffer is added to its own PVFS_dev_map_desc structure
which also describes its total size, as well as the size and number of
the partitions.

A pointer to the IO buffer's PVFS_dev_map_desc structure is sent to a
mapping routine in the kernel module with an ioctl. The structure is
copied from user space to kernel space with copy_from_user and is used
to initialize the kernel module's "bufmap" (struct orangefs_bufmap), which
then contains:

  * refcnt - a reference counter
  * desc_size - PVFS2_BUFMAP_DEFAULT_DESC_SIZE (4194304) - the IO buffer's
    partition size, which represents the filesystem's block size and
    is used for s_blocksize in super blocks.
  * desc_count - PVFS2_BUFMAP_DEFAULT_DESC_COUNT (10) - the number of
    partitions in the IO buffer.
  * desc_shift - log2(desc_size), used for s_blocksize_bits in super blocks.
  * total_size - the total size of the IO buffer.
  * page_count - the number of 4096 byte pages in the IO buffer.
  * page_array - a pointer to page_count * (sizeof(struct page*)) bytes
    of kcalloced memory. This memory is used as an array of pointers
    to each of the pages in the IO buffer through a call to get_user_pages.
  * desc_array - a pointer to desc_count * (sizeof(struct orangefs_bufmap_desc))
    bytes of kcalloced memory. This memory is further intialized:

      user_desc is the kernel's copy of the IO buffer's ORANGEFS_dev_map_desc
      structure. user_desc->ptr points to the IO buffer.

      pages_per_desc = bufmap->desc_size / PAGE_SIZE
      offset = 0

        bufmap->desc_array[0].page_array = &bufmap->page_array[offset]
        bufmap->desc_array[0].array_count = pages_per_desc = 1024
        bufmap->desc_array[0].uaddr = (user_desc->ptr) + (0 * 1024 * 4096)
        offset += 1024
                           .
                           .
                           .
        bufmap->desc_array[9].page_array = &bufmap->page_array[offset]
        bufmap->desc_array[9].array_count = pages_per_desc = 1024
        bufmap->desc_array[9].uaddr = (user_desc->ptr) +
                                               (9 * 1024 * 4096)
        offset += 1024

  * buffer_index_array - a desc_count sized array of ints, used to
    indicate which of the IO buffer's partitions are available to use.
  * buffer_index_lock - a spinlock to protect buffer_index_array during update.
  * readdir_index_array - a five (ORANGEFS_READDIR_DEFAULT_DESC_COUNT) element
    int array used to indicate which of the readdir buffer's partitions are
    available to use.
  * readdir_index_lock - a spinlock to protect readdir_index_array during
    update.

OPERATIONS:

The kernel module builds an "op" (struct orangefs_kernel_op_s) when it
needs to communicate with userspace. Part of the op contains the "upcall"
which expresses the request to userspace. Part of the op eventually
contains the "downcall" which expresses the results of the request.

The slab allocator is used to keep a cache of op structures handy.

The life cycle of a typical op goes like this:

  - obtain and initialize an op structure from the op_cache.

  - queue the op to the pvfs device so that its upcall data can be
    read by userspace.

  - wait for userspace to write downcall data back to the pvfs device.

  - consume the downcall and return the op struct to the op_cache.

Some ops are atypical with respect to their payloads: readdir and io ops.

  - readdir ops use the smaller of the two pre-allocated pre-partitioned
    memory buffers. The readdir buffer is only available to userspace.
    The kernel module obtains an index to a free partition before launching
    a readdir op. Userspace deposits the results into the indexed partition
    and then writes them to back to the pvfs device.

  - io (read and write) ops use the larger of the two pre-allocated
    pre-partitioned memory buffers. The IO buffer is accessible from
    both userspace and the kernel module. The kernel module obtains an
    index to a free partition before launching an io op. The kernel module
    deposits write data into the indexed partition, to be consumed
    directly by userspace. Userspace deposits the results of read
    requests into the indexed partition, to be consumed directly
    by the kernel module.

Responses to kernel requests are all packaged in pvfs2_downcall_t
structs. Besides a few other members, pvfs2_downcall_t contains a
union of structs, each of which is associated with a particular
response type.

The several members outside of the union are:
 - int32_t type - type of operation.
 - int32_t status - return code for the operation.
 - int64_t trailer_size - 0 unless readdir operation.
 - char *trailer_buf - initialized to NULL, used during readdir operations.

The appropriate member inside the union is filled out for any
particular response.

  PVFS2_VFS_OP_FILE_IO
    fill a pvfs2_io_response_t

  PVFS2_VFS_OP_LOOKUP
    fill a PVFS_object_kref

  PVFS2_VFS_OP_CREATE
    fill a PVFS_object_kref

  PVFS2_VFS_OP_SYMLINK
    fill a PVFS_object_kref

  PVFS2_VFS_OP_GETATTR
    fill in a PVFS_sys_attr_s (tons of stuff the kernel doesn't need)
    fill in a string with the link target when the object is a symlink.

  PVFS2_VFS_OP_MKDIR
    fill a PVFS_object_kref

  PVFS2_VFS_OP_STATFS
    fill a pvfs2_statfs_response_t with useless info <g>. It is hard for
    us to know, in a timely fashion, these statistics about our
    distributed network filesystem. 

  PVFS2_VFS_OP_FS_MOUNT
    fill a pvfs2_fs_mount_response_t which is just like a PVFS_object_kref
    except its members are in a different order and "__pad1" is replaced
    with "id".

  PVFS2_VFS_OP_GETXATTR
    fill a pvfs2_getxattr_response_t

  PVFS2_VFS_OP_LISTXATTR
    fill a pvfs2_listxattr_response_t

  PVFS2_VFS_OP_PARAM
    fill a pvfs2_param_response_t

  PVFS2_VFS_OP_PERF_COUNT
    fill a pvfs2_perf_count_response_t

  PVFS2_VFS_OP_FSKEY
    file a pvfs2_fs_key_response_t

  PVFS2_VFS_OP_READDIR
    jamb everything needed to represent a pvfs2_readdir_response_t into
    the readdir buffer descriptor specified in the upcall.

writev() on /dev/pvfs2-req is used to pass responses to the requests
made by the kernel side.

A buffer_list containing:
  - a pointer to the prepared response to the request from the
    kernel (struct pvfs2_downcall_t).
  - and also, in the case of a readdir request, a pointer to a
    buffer containing descriptors for the objects in the target
    directory.
... is sent to the function (PINT_dev_write_list) which performs
the writev.

PINT_dev_write_list has a local iovec array: struct iovec io_array[10];

The first four elements of io_array are initialized like this for all
responses:

  io_array[0].iov_base = address of local variable "proto_ver" (int32_t)
  io_array[0].iov_len = sizeof(int32_t)

  io_array[1].iov_base = address of global variable "pdev_magic" (int32_t)
  io_array[1].iov_len = sizeof(int32_t)
  
  io_array[2].iov_base = address of parameter "tag" (PVFS_id_gen_t)
  io_array[2].iov_len = sizeof(int64_t)

  io_array[3].iov_base = address of out_downcall member (pvfs2_downcall_t)
                         of global variable vfs_request (vfs_request_t)
  io_array[3].iov_len = sizeof(pvfs2_downcall_t)

Readdir responses initialize the fifth element io_array like this:

  io_array[4].iov_base = contents of member trailer_buf (char *)
                         from out_downcall member of global variable
                         vfs_request
  io_array[4].iov_len = contents of member trailer_size (PVFS_size)
                        from out_downcall member of global variable
                        vfs_request