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

Benny Halevy
2010-09-13T11:20:59Z

On 2010-09-10 22:23, Trond Myklebust wrote:
> 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.
>

We call these methods upon creating and destroying the nfs_server,
respectively. Later on, in the post-submit world, we change this parameter
to a struct nfs_server * for the blocks layout driver.
The motivation is to issue GETDEVICELIST at mount time.

For the file layout at its present state we only use the nfs_client
for the deviceid cache. Note that to support multiple layout types
per server (possibly for different filesystems exported by that server
we'll need per-layouttype deviceid cache on the nfs_client.

We can have different methods for the per-nfs_client event
and the per-nfs_server event and call them correspondingly.

Benny

>> 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 *);
>>
>
>
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