Re: [PATCH 07/13] RFC: pnfs: full mount/umount infrastructure

[Trond Myklebust <Trond.Myklebust@netapp.com>]

On Thu, 2010-09-02 at 14:00 -0400, Fred Isaman wrote:
> From: The pNFS Team <linux-nfs@vger.kernel.org>
> 
> 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: TBD - melding/reorganization of several patches
> ---
>  Documentation/filesystems/nfs/00-INDEX |    2 +
>  Documentation/filesystems/nfs/pnfs.txt |   48 +++++++++++++++++++
>  fs/nfs/Kconfig                         |    2 +-
>  fs/nfs/pnfs.c                          |   79 +++++++++++++++++++++++++++++++-
>  fs/nfs/pnfs.h                          |   14 ++++++
>  5 files changed, 142 insertions(+), 3 deletions(-)
>  create mode 100644 Documentation/filesystems/nfs/pnfs.txt
> 
> diff --git a/Documentation/filesystems/nfs/00-INDEX b/Documentation/filesystems/nfs/00-INDEX
> index 2f68cd6..8d930b9 100644
> --- a/Documentation/filesystems/nfs/00-INDEX
> +++ b/Documentation/filesystems/nfs/00-INDEX
> @@ -12,5 +12,7 @@ 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 code
>  rpc-cache.txt
>  	- introduction to the caching mechanisms in the sunrpc layer.
> diff --git a/Documentation/filesystems/nfs/pnfs.txt b/Documentation/filesystems/nfs/pnfs.txt
> new file mode 100644
> index 0000000..bc0b9cf
> --- /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.
> diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
> index 6c2aad4..5f1b936 100644
> --- a/fs/nfs/Kconfig
> +++ b/fs/nfs/Kconfig
> @@ -78,7 +78,7 @@ config NFS_V4_1
>  	depends on NFS_V4 && EXPERIMENTAL
>  	help
>  	  This option enables support for minor version 1 of the NFSv4 protocol
> -	  (draft-ietf-nfsv4-minorversion1) in the kernel's NFS client.
> +	  (RFC 5661) in the kernel's NFS client.
>  
>  	  If unsure, say N.
>  
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index 2e5dba1..8d503fc 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -32,16 +32,48 @@
>  
>  #define NFSDBG_FACILITY		NFSDBG_PNFS
>  
> -/* STUB that returns the equivalent of "no module found" */
> +/* Locking:
> + *
> + * pnfs_spinlock:
> + *      protects pnfs_modules_tbl.
> + */
> +static DEFINE_SPINLOCK(pnfs_spinlock);
> +
> +/*
> + * pnfs_modules_tbl holds all pnfs modules
> + */
> +static LIST_HEAD(pnfs_modules_tbl);
> +
> +/* Return the registered pnfs layout driver module matching given id */
> +static struct pnfs_layoutdriver_type *
> +find_pnfs_driver_locked(u32 id) {
> +	struct  pnfs_layoutdriver_type *local;
> +
> +	dprintk("PNFS: %s: Searching for %u\n", __func__, id);
> +	list_for_each_entry(local, &pnfs_modules_tbl, pnfs_tblid)
> +		if (local->id == id)
> +			goto out;
> +	local = NULL;
> +out:
> +	return local;
> +}
> +
>  static struct pnfs_layoutdriver_type *
>  find_pnfs_driver(u32 id) {
> -	return NULL;
> +	struct  pnfs_layoutdriver_type *local;
> +
> +	spin_lock(&pnfs_spinlock);
> +	local = find_pnfs_driver_locked(id);

Don't you want some kind of reference count on this? I'd assume that you
probably need a module_get() with a corresponding module_put() when you
are done using the layoutdriver.

> +	spin_unlock(&pnfs_spinlock);
> +	return local;
>  }
>  
>  /* Unitialize a mountpoint in a layout driver */
>  void
>  unset_pnfs_layoutdriver(struct nfs_server *nfss)
>  {
> +	if (nfss->pnfs_curr_ld)
> +		nfss->pnfs_curr_ld->ld_io_ops->uninitialize_mountpoint(nfss->nfs_client);

That 'uninitialize_mountpoint' name doesn't make any sense. The
nfs_client parameter isn't associated to a particular mountpoint.

>  	nfss->pnfs_curr_ld = NULL;
>  }
>  
> @@ -68,6 +100,12 @@ set_pnfs_layoutdriver(struct nfs_server *server, u32 id)
>  			goto out_no_driver;
>  		}
>  	}
> +	if (ld_type->ld_io_ops->initialize_mountpoint(server->nfs_client)) {

Ditto.

> +		printk(KERN_ERR
> +		       "%s: Error initializing mount point for layout driver %u.\n",
> +		       __func__, id);
> +		goto out_no_driver;
> +	}
>  	server->pnfs_curr_ld = ld_type;
>  	dprintk("%s: pNFS module for %u set\n", __func__, id);
>  	return;
> @@ -76,3 +114,40 @@ out_no_driver:
>  	dprintk("%s: Using NFSv4 I/O\n", __func__);
>  	server->pnfs_curr_ld = NULL;
>  }
> +
> +int
> +pnfs_register_layoutdriver(struct pnfs_layoutdriver_type *ld_type)
> +{
> +	struct layoutdriver_io_operations *io_ops = ld_type->ld_io_ops;
> +	int status = -EINVAL;
> +
> +	if (!io_ops) {
> +		printk(KERN_ERR "%s Layout driver must provide io_ops\n",
> +			__func__);
> +		return status;
> +	}
> +
> +	spin_lock(&pnfs_spinlock);
> +	if (!find_pnfs_driver_locked(ld_type->id)) {
> +		list_add(&ld_type->pnfs_tblid, &pnfs_modules_tbl);
> +		status = 0;
> +		dprintk("%s Registering id:%u name:%s\n", __func__, ld_type->id,
> +			ld_type->name);
> +	} else
> +		printk(KERN_ERR "%s Module with id %d already loaded!\n",
> +			__func__, ld_type->id);
> +	spin_unlock(&pnfs_spinlock);
> +
> +	return status;
> +}
> +EXPORT_SYMBOL(pnfs_register_layoutdriver);
> +
> +void
> +pnfs_unregister_layoutdriver(struct pnfs_layoutdriver_type *ld_type)
> +{
> +	dprintk("%s Deregistering id:%u\n", __func__, ld_type->id);
> +	spin_lock(&pnfs_spinlock);
> +	list_del(&ld_type->pnfs_tblid);
> +	spin_unlock(&pnfs_spinlock);
> +}
> +EXPORT_SYMBOL(pnfs_unregister_layoutdriver);
> diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
> index 3281fbf..9049b9a 100644
> --- a/fs/nfs/pnfs.h
> +++ b/fs/nfs/pnfs.h
> @@ -16,8 +16,22 @@
>  
>  /* Per-layout driver specific registration structure */
>  struct pnfs_layoutdriver_type {
> +	struct list_head pnfs_tblid;
> +	const u32 id;
> +	const char *name;
> +	struct layoutdriver_io_operations *ld_io_ops;
>  };
>  
> +/* Layout driver I/O operations. */
> +struct layoutdriver_io_operations {
> +	/* Registration information for a new mounted file system */
> +	int (*initialize_mountpoint) (struct nfs_client *);
> +	int (*uninitialize_mountpoint) (struct nfs_client *);
> +};
> +
> +extern int pnfs_register_layoutdriver(struct pnfs_layoutdriver_type *);
> +extern void pnfs_unregister_layoutdriver(struct pnfs_layoutdriver_type *);
> +
>  void set_pnfs_layoutdriver(struct nfs_server *, u32 id);
>  void unset_pnfs_layoutdriver(struct nfs_server *);
>