Re: [PATCH 37/37] nfsd: add some comments to the nfsd4 object definitions

["J. Bruce Fields" <bfields@fieldses.org>]

Thanks for the documentation!  A couple comments:

On Wed, Jul 30, 2014 at 08:27:38AM -0400, Jeff Layton wrote:
> Add some comments that describe what each of these objects is, and how
> they related to one another.
> 
> Signed-off-by: Jeff Layton <jlayton@primarydata.com>
> ---
>  fs/nfsd/netns.h |  8 +++++
>  fs/nfsd/state.h | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++++-----
>  2 files changed, 92 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
> index 3831ef6e5c75..46680da55cd7 100644
> --- a/fs/nfsd/netns.h
> +++ b/fs/nfsd/netns.h
> @@ -34,6 +34,14 @@
>  struct cld_net;
>  struct nfsd4_client_tracking_ops;
>  
> +/*
> + * Represents a nfsd "container". With respect to nfsv4 state tracking, the
> + * fields of interest are the *_id_hashtbls and the *_name_tree. These track
> + * the nfs4_client objects by either short or long form clientid.
> + *
> + * Each nfsd_net runs a nfs4_laundromat workqueue job every lease period to

It's a little more complicated than that suggests--maybe replace "every
lease period" by "when necessary"?

> + * clean up expired clients and delegations within the container.
> + */
>  struct nfsd_net {
>  	struct cld_net *cld_net;
>  
> diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
> index a363f6bb621e..52ccd07d92ed 100644
> --- a/fs/nfsd/state.h
> +++ b/fs/nfsd/state.h
> @@ -72,6 +72,11 @@ struct nfsd4_callback {
>  	bool cb_done;
>  };
>  
> +/*
> + * A core object that represents a "common" stateid. These are generally
> + * embedded within the different (more specific) stateid objects and contain
> + * fields that are of general use to any stateid.
> + */
>  struct nfs4_stid {
>  	atomic_t sc_count;
>  #define NFS4_OPEN_STID 1
> @@ -89,6 +94,18 @@ struct nfs4_stid {
>  	void (*sc_free)(struct nfs4_stid *);
>  };
>  
> +/*
> + * Represents a delegation stateid. The nfs4_client holds references to these
> + * and they are put when it is being destroyed or when the delegation is
> + * returned by the client.

This might be worth another sentence or two.  I believe the references
are:

	- 1 reference as long as a delegation is still in force (taken
	  when it's alloc'd, put when it's returned or revoked)
	- 1 reference as long as a recall rpc is in progress (taken when
	  the lease is broken, put when the rpc exits.
	- 1 more ephemeral reference for each nfsd thread currently
	  doing something with that delegation without holding
	  cl_lock?

(By the way, I wonder if that list_for_each_entry() at the end of
nfsd4_process_cb_update actually does anything: hasn't
nfsd4_cb_recall_release() already run and removed any delegation from
the cl_callbacks list?  I may just be forgetting how this works.)

--b.

> + * If the server attempts to recall a delegation and the client doesn't do so
> + * before a timeout, the server may also revoke the delegation. In that case,
> + * the object will either be destroyed (v4.0) or moved to a per-client list of
> + * revoked delegations (v4.1+).
> + *
> + * This object is a superset of the nfs4_stid.
> + */
>  struct nfs4_delegation {
>  	struct nfs4_stid	dl_stid; /* must be first field */
>  	struct list_head	dl_perfile;
> @@ -195,6 +212,11 @@ struct nfsd4_conn {
>  	unsigned char cn_flags;
>  };
>  
> +/*
> + * Representation of a v4.1+ session. These are refcounted in a similar fashion
> + * to the nfs4_client. References are only taken when the server is actively
> + * working on the object (primarily during the processing of compounds).
> + */
>  struct nfsd4_session {
>  	atomic_t		se_ref;
>  	struct list_head	se_hash;	/* hash by sessionid */
> @@ -224,13 +246,30 @@ struct nfsd4_sessionid {
>  
>  /*
>   * struct nfs4_client - one per client.  Clientids live here.
> - * 	o Each nfs4_client is hashed by clientid.
>   *
> - * 	o Each nfs4_clients is also hashed by name 
> - * 	  (the opaque quantity initially sent by the client to identify itself).
> + * The initial object created by an NFS client using SETCLIENTID (for NFSv4.0)
> + * or EXCHANGE_ID (for NFSv4.1+). These objects are refcounted and timestamped.
> + * Each nfsd_net_ns object contains a set of these and they are tracked via
> + * short and long form clientid. They are hashed and searched for under the
> + * per-nfsd_net client_lock spinlock.
> + *
> + * References to it are only held during the processing of compounds, and in
> + * certain other operations. In their "resting state" they have a refcount of
> + * 0. If they are not renewed within a lease period, they become eligible for
> + * destruction by the laundromat.
> + *
> + * These objects can also be destroyed prematurely by the fault injection code,
> + * or if the client sends certain forms of SETCLIENTID or EXCHANGE_ID updates.
> + * Care is taken *not* to do this however when the objects have an elevated
> + * refcount.
> + *
> + * o Each nfs4_client is hashed by clientid
> + *
> + * o Each nfs4_clients is also hashed by name (the opaque quantity initially
> + *   sent by the client to identify itself).
>   * 	  
> - *	o cl_perclient list is used to ensure no dangling stateowner references
> - *	  when we expire the nfs4_client
> + * o cl_perclient list is used to ensure no dangling stateowner references
> + *   when we expire the nfs4_client
>   */
>  struct nfs4_client {
>  	struct list_head	cl_idhash; 	/* hash by cl_clientid.id */
> @@ -340,6 +379,12 @@ struct nfs4_stateowner_operations {
>  	void (*so_free)(struct nfs4_stateowner *);
>  };
>  
> +/*
> + * A core object that represents either an open or lock owner. The object and
> + * lock owner objects have one of these embedded within them. Refcounts and
> + * other fields common to both owner types are contained within these
> + * structures.
> + */
>  struct nfs4_stateowner {
>  	struct list_head			so_strhash;
>  	struct list_head			so_stateids;
> @@ -354,6 +399,12 @@ struct nfs4_stateowner {
>  	bool					so_is_open_owner;
>  };
>  
> +/*
> + * When a file is opened, the client provides an open state owner opaque string
> + * that indicates the "owner" of that open. These objects are refcounted.
> + * References to it are held by each open state associated with it. This object
> + * is a superset of the nfs4_stateowner struct.
> + */
>  struct nfs4_openowner {
>  	struct nfs4_stateowner	oo_owner; /* must be first field */
>  	struct list_head        oo_perclient;
> @@ -371,6 +422,12 @@ struct nfs4_openowner {
>  	unsigned char		oo_flags;
>  };
>  
> +/*
> + * Represents a generic "lockowner". Similar to an openowner. References to it
> + * are held by the lock stateids that are created on its behalf. This object is
> + * a superset of the nfs4_stateowner struct (or would be if it needed any extra
> + * fields).
> + */
>  struct nfs4_lockowner {
>  	struct nfs4_stateowner	lo_owner; /* must be first element */
>  };
> @@ -385,7 +442,14 @@ static inline struct nfs4_lockowner * lockowner(struct nfs4_stateowner *so)
>  	return container_of(so, struct nfs4_lockowner, lo_owner);
>  }
>  
> -/* nfs4_file: a file opened by some number of (open) nfs4_stateowners. */
> +/*
> + * nfs4_file: a file opened by some number of (open) nfs4_stateowners.
> + *
> + * These objects are global. nfsd only keeps one instance of a nfs4_file per
> + * inode (though it may keep multiple file descriptors open per inode). These
> + * are tracked in the file_hashtbl which is protected by the state_lock
> + * spinlock.
> + */
>  struct nfs4_file {
>  	atomic_t		fi_ref;
>  	spinlock_t		fi_lock;
> @@ -410,7 +474,20 @@ struct nfs4_file {
>  	bool			fi_had_conflict;
>  };
>  
> -/* "ol" stands for "Open or Lock".  Better suggestions welcome. */
> +/*
> + * A generic struct representing either a open or lock stateid. The nfs4_client
> + * holds a reference to each of these objects, and they in turn hold a
> + * reference to their respective stateowners. The client's reference is
> + * released in response to a close or unlock (depending on whether it's an open
> + * or lock stateid) or when the client is being destroyed.
> + *
> + * In the case of v4.0 open stateids, these objects are preserved for a little
> + * while after close in order to handle CLOSE replays. Those are eventually
> + * reclaimed via a LRU scheme by the laundromat.
> + *
> + * This object is a superset of the nfs4_stid. "ol" stands for "Open or Lock".
> + * Better suggestions welcome.
> + */
>  struct nfs4_ol_stateid {
>  	struct nfs4_stid    st_stid; /* must be first field */
>  	struct list_head              st_perfile;
> -- 
> 1.9.3
> 
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