diff options
author | Fred Isaman <iisaman@netapp.com> | 2010-10-20 06:17:59 +0200 |
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committer | Trond Myklebust <Trond.Myklebust@netapp.com> | 2010-10-25 00:07:10 +0200 |
commit | 02c35fca7cf4ea2dfdc6db279e230cacbbf4b870 (patch) | |
tree | 7449a8a3fb119d862f6c163c05cf43d58443c377 /Documentation | |
parent | NFS: set layout driver (diff) | |
download | linux-02c35fca7cf4ea2dfdc6db279e230cacbbf4b870.tar.xz linux-02c35fca7cf4ea2dfdc6db279e230cacbbf4b870.zip |
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 <iisaman@netapp.com>
Signed-off-by: Marc Eshel <eshel@almaden.ibm.com>
Signed-off-by: Andy Adamson<andros@netapp.com>
Signed-off-by: Bian Naimeng <biannm@cn.fujitsu.com>
Signed-off-by: Benny Halevy <bhalevy@panasas.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/filesystems/nfs/00-INDEX | 2 | ||||
-rw-r--r-- | Documentation/filesystems/nfs/pnfs.txt | 48 |
2 files changed, 50 insertions, 0 deletions
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. |