Date: Mon, 3 Jun 2013 18:00:24 -0400
From: "J. Bruce Fields" <bfields@fieldses.org>
To: Jeff Layton <jlayton@redhat.com>
Cc: viro@zeniv.linux.org.uk, matthew@wil.cx, dhowells@redhat.com,
        sage@inktank.com, smfrench@gmail.com, swhiteho@redhat.com,
        Trond.Myklebust@netapp.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, linux-afs@lists.infradead.org,
        ceph-devel@vger.kernel.org, linux-cifs@vger.kernel.org,
        samba-technical@lists.samba.org, cluster-devel@redhat.com,
        linux-nfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        piastryyy@gmail.com
Subject: Re: [PATCH v1 03/11] locks: comment cleanups and clarifications
Message-ID: <20130603220024.GF2109@fieldses.org>
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 <1370056054-25449-4-git-send-email-jlayton@redhat.com>
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On Fri, May 31, 2013 at 11:07:26PM -0400, Jeff Layton wrote:
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/locks.c         |   24 +++++++++++++++++++-----
>  include/linux/fs.h |    6 ++++++
>  2 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/locks.c b/fs/locks.c
> index e3140b8..a7d2253 100644
> --- a/fs/locks.c
> +++ b/fs/locks.c
> @@ -150,6 +150,16 @@ static int target_leasetype(struct file_lock *fl)
>  int leases_enable = 1;
>  int lease_break_time = 45;
>  
> +/*
> + * The i_flock list is ordered by:
> + *
> + * 1) lock type -- FL_LEASEs first, then FL_FLOCK, and finally FL_POSIX
> + * 2) lock owner
> + * 3) lock range start
> + * 4) lock range end
> + *
> + * Obviously, the last two criteria only matter for POSIX locks.
> + */

Thanks, yes, that needs documenting!  Though I wonder if this is the
place people will look for it.

>  #define for_each_lock(inode, lockp) \
>  	for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)
>  
> @@ -806,6 +816,11 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
>  	}
>  
>  	lock_flocks();
> +	/*
> +	 * New lock request. Walk all POSIX locks and look for conflicts. If
> +	 * there are any, either return -EAGAIN or put the request on the
> +	 * blocker's list of waiters.
> +	 */

This though, seems a) not 100% accurate (it could also return EDEADLCK,
for example), b) mostly redundant with respect to the following code.

>  	if (request->fl_type != F_UNLCK) {
>  		for_each_lock(inode, before) {
>  			fl = *before;
> @@ -844,7 +859,7 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
>  		before = &fl->fl_next;
>  	}
>  
> -	/* Process locks with this owner.  */
> +	/* Process locks with this owner. */
>  	while ((fl = *before) && posix_same_owner(request, fl)) {
>  		/* Detect adjacent or overlapping regions (if same lock type)
>  		 */
> @@ -930,10 +945,9 @@ static int __posix_lock_file(struct inode *inode, struct file_lock *request, str
>  	}
>  
>  	/*
> -	 * The above code only modifies existing locks in case of
> -	 * merging or replacing.  If new lock(s) need to be inserted
> -	 * all modifications are done bellow this, so it's safe yet to
> -	 * bail out.
> +	 * The above code only modifies existing locks in case of merging or
> +	 * replacing. If new lock(s) need to be inserted all modifications are
> +	 * done below this, so it's safe yet to bail out.
>  	 */
>  	error = -ENOLCK; /* "no luck" */
>  	if (right && left == right && !new_fl2)
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index b9d7816..ae377e9 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -926,6 +926,12 @@ int locks_in_grace(struct net *);
>  /* that will die - we need it for nfs_lock_info */
>  #include <linux/nfs_fs_i.h>
>  
> +/*
> + * struct file_lock represents a generic "file lock". It's used to represent
> + * POSIX byte range locks, BSD (flock) locks, and leases. It's important to
> + * note that the same struct is used to represent both a request for a lock and
> + * the lock itself, but the same object is never used for both.

Yes, and I do find that confusing.  I wonder if there's a sensible way
to use separate structs for the different uses.

--b.

> + */
>  struct file_lock {
>  	struct file_lock *fl_next;	/* singly linked list for this inode  */
>  	struct list_head fl_link;	/* doubly linked list of all locks */
> -- 
> 1.7.1
> 
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