On Fri, May 31, 2013 at 11:07:26PM -0400, Jeff Layton wrote:
> Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
> 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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