From 02c35fca7cf4ea2dfdc6db279e230cacbbf4b870 Mon Sep 17 00:00:00 2001 From: Fred Isaman Date: Wed, 20 Oct 2010 00:17:59 -0400 Subject: NFSv4.1: pnfs: full mount/umount infrastructure Allow a module implementing a layout type to register, and have its mount/umount routines called for filesystems that the server declares support it. Signed-off-by: Fred Isaman Signed-off-by: Marc Eshel Signed-off-by: Andy Adamson Signed-off-by: Bian Naimeng Signed-off-by: Benny Halevy Signed-off-by: Trond Myklebust --- Documentation/filesystems/nfs/00-INDEX | 2 ++ Documentation/filesystems/nfs/pnfs.txt | 48 ++++++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+) create mode 100644 Documentation/filesystems/nfs/pnfs.txt (limited to 'Documentation/filesystems') diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX index 3225a5662114..a57e12411d2a 100644 --- a/Documentation/filesystems/nfs/00-INDEX +++ b/Documentation/filesystems/nfs/00-INDEX @@ -12,6 +12,8 @@ nfs-rdma.txt - how to install and setup the Linux NFS/RDMA client and server software nfsroot.txt - short guide on setting up a diskless box with NFS root filesystem. +pnfs.txt + - short explanation of some of the internals of the pnfs client code rpc-cache.txt - introduction to the caching mechanisms in the sunrpc layer. idmapper.txt diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt new file mode 100644 index 000000000000..bc0b9cfe095b --- /dev/null +++ b/Documentation/filesystems/nfs/pnfs.txt @@ -0,0 +1,48 @@ +Reference counting in pnfs: +========================== + +The are several inter-related caches. We have layouts which can +reference multiple devices, each of which can reference multiple data servers. +Each data server can be referenced by multiple devices. Each device +can be referenced by multiple layouts. To keep all of this straight, +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 of these layout +segments in nfsi->layout, of type struct pnfs_layout_hdr. + +We reference the header for the inode pointing to it, across each +outstanding RPC call that references it (LAYOUTGET, LAYOUTRETURN, +LAYOUTCOMMIT), and for each lseg held within. + +Each header is also (when non-empty) put on a list associated with +struct nfs_client (cl_layouts). Being put on this list does not bump +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 +mount. The entries (struct nfs4_deviceid) themselves are held across +the lifetime of each lseg referencing them. + +RCU is used because the deviceid is basically a write once, read many +data structure. The hlist size of 32 buckets needs better +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 + +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. -- cgit v1.2.1