Commit 34e75cf4 authored by Daniel W. S. Almeida's avatar Daniel W. S. Almeida Committed by Jonathan Corbet
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Documentation: nfs: convert pnfs.txt to ReST 



Convert pnfs.txt to ReST. Content remains mostly unchanged.

Signed-off-by: default avatarDaniel W. S. Almeida <dwlsalmeida@gmail.com>
Link: https://lore.kernel.org/r/20200129044917.566906-2-dwlsalmeida@gmail.com


Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent bb6d3fb3

Documentation/filesystems/index.rst

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@@ -51,3 +51,4 @@ Documentation for filesystem implementations. 
   overlayfs

   virtiofs

   vfat

   nfs/index

Documentation/filesystems/nfs/index.rst

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+9 −0
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===============================

NFS

===============================





.. toctree::

   :maxdepth: 1



   pnfs

Documentation/filesystems/nfs/pnfs.txt→Documentation/filesystems/nfs/pnfs.rst

+15 −10
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Reference counting in pnfs:

==========================

Reference counting in pnfs

==========================



The are several inter-related caches.  We have layouts which can
@@ -9,7 +10,8 @@ we need to reference count. 




struct pnfs_layout_hdr

----------------------

======================



The on-the-wire command LAYOUTGET corresponds to struct

pnfs_layout_segment, usually referred to by the variable name lseg.

Each nfs_inode may hold a pointer to a cache of these layout
@@ -25,7 +27,8 @@ the reference count, as the layout is kept around by the lseg that 
keeps it in the list.



deviceid_cache

--------------

==============



lsegs reference device ids, which are resolved per nfs_client and

layout driver type.  The device ids are held in a RCU cache (struct

nfs4_deviceid_cache).  The cache itself is referenced across each
@@ -38,24 +41,26 @@ justification, but seems reasonable given that we can have multiple 
deviceid's per filesystem, and multiple filesystems per nfs_client.



The hash code is copied from the nfsd code base.  A discussion of

hashing and variations of this algorithm can be found at:

http://groups.google.com/group/comp.lang.c/browse_thread/thread/9522965e2b8d3809

hashing and variations of this algorithm can be found `here.

<http://groups.google.com/group/comp.lang.c/browse_thread/thread/9522965e2b8d3809>`_



data server cache

-----------------

=================



file driver devices refer to data servers, which are kept in a module

level cache.  Its reference is held over the lifetime of the deviceid

pointing to it.



lseg

----

====



lseg maintains an extra reference corresponding to the NFS_LSEG_VALID

bit which holds it in the pnfs_layout_hdr's list.  When the final lseg

is removed from the pnfs_layout_hdr's list, the NFS_LAYOUT_DESTROYED

bit is set, preventing any new lsegs from being added.



layout drivers

--------------

==============



PNFS utilizes what is called layout drivers. The STD defines 4 basic

layout types: "files", "objects", "blocks", and "flexfiles". For each
@@ -68,6 +73,6 @@ Blocks-layout-driver code is in: fs/nfs/blocklayout/.. directory 
Flexfiles-layout-driver code is in: fs/nfs/flexfilelayout/.. directory



blocks-layout setup

-------------------

===================



TODO: Document the setup needs of the blocks layout driver