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Message-Id: <20090407160615.0815aadd.akpm@linux-foundation.org>
Date: Tue, 7 Apr 2009 16:06:15 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Eric Paris <eparis@...hat.com>
Cc: linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
hch@...radead.org, alan@...rguk.ukuu.org.uk, sfr@...b.auug.org.au,
john@...nmccutchan.com, rlove@...ve.org
Subject: Re: [PATCH -V2 04/13] fsnotify: add in inode fsnotify markings
On Fri, 27 Mar 2009 16:05:26 -0400
Eric Paris <eparis@...hat.com> wrote:
> This patch creates in inode fsnotify markings. dnotify will make use of in
> inode markings to mark which inodes it wishes to send events for.
The text appears to be using the term "in inode" as a term-of-art. But
it's a new one to me.
> fanotify
> will use this to mark which inodes it does not wish to send events for.
>
<but i dont know what fanotify is>
> ---
>
> Documentation/filesystems/fsnotify.txt | 180 +++++++++++++++++++++++++
> fs/inode.c | 9 +
> fs/notify/Makefile | 2
> fs/notify/fsnotify.c | 10 +
> fs/notify/fsnotify.h | 3
> fs/notify/group.c | 33 ++++-
> fs/notify/inode_mark.c | 229 ++++++++++++++++++++++++++++++++
> include/linux/fs.h | 5 +
> include/linux/fsnotify.h | 9 +
> include/linux/fsnotify_backend.h | 58 ++++++++
> 10 files changed, 535 insertions(+), 3 deletions(-)
> create mode 100644 Documentation/filesystems/fsnotify.txt
> create mode 100644 fs/notify/inode_mark.c
>
> diff --git a/Documentation/filesystems/fsnotify.txt b/Documentation/filesystems/fsnotify.txt
> new file mode 100644
> index 0000000..e1c90f5
> --- /dev/null
> +++ b/Documentation/filesystems/fsnotify.txt
> @@ -0,0 +1,180 @@
> +fsnotify inode mark locking/lifetime/and refcnting
> +
> +struct fsnotify_mark_entry {
> + __u32 mask; /* mask this mark entry is for */
> + /* we hold ref for each i_list and g_list. also one ref for each 'thing'
> + * in kernel that found and may be using this mark. */
> + atomic_t refcnt; /* active things looking at this mark */
> + struct inode *inode; /* inode this entry is associated with */
> + struct fsnotify_group *group; /* group this mark entry is for */
> + struct hlist_node i_list; /* list of mark_entries by inode->i_fsnotify_mark_entries */
> + struct list_head g_list; /* list of mark_entries by group->i_fsnotify_mark_entries */
> + spinlock_t lock; /* protect group, inode, and killme */
> + struct list_head free_i_list; /* tmp list used when freeing this mark */
> + struct list_head free_g_list; /* tmp list used when freeing this mark */
> + void (*free_mark)(struct fsnotify_mark_entry *entry); /* called on final put+free */
> +};
> +
> +REFCNT:
> +The mark->refcnt tells how many "things" in the kernel currectly are
"currently"
>
> ...
>
> +The inode mark can be cleared for a number of different reasons including:
> +- The inode is unlinked for the last time. (fsnotify_inoderemove)
> +- The inode is being evicted from cache. (fsnotify_inode_delete)
> +- The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
So it did want to be called fsnotify_inode_remove.
> +- Something explicitly requests that it be removed. (fsnotify_destroy_mark_by_entry)
> +- The fsnotify_group associated with the mark is going away and all such marks
> + need to be cleaned up. (fsnotify_clear_marks_by_group)
> +
> +Worst case we are given an inode and need to clean up all the marks on that
> +inode. We take i_lock and walk the i_fsnotify_mark_entries safely. For each
> +mark on the list we take a reference (so the mark can't disappear under us).
> +We remove that mark form the inode's list of marks and we add this mark to a
> +private list anchored on the stack using i_free_list; At this point we no
> +longer fear anything finding the mark using the inode's list of marks.
damn, I wish this was all written in the C files instead.
>
> ...
>
> +void fsnotify_recalc_group_mask(struct fsnotify_group *group)
> +{
> + __u32 mask = 0;
> + __u32 old_mask = group->mask;
> + struct fsnotify_mark_entry *entry;
> +
> + spin_lock(&group->mark_lock);
> + list_for_each_entry(entry, &group->mark_entries, g_list) {
> + mask |= entry->mask;
> + }
unneeded {} (numerous places)
> + spin_unlock(&group->mark_lock);
> +
> + group->mask = mask;
> +
> + if (old_mask != mask)
> + fsnotify_recalc_global_mask();
> +}
> +
> static void fsnotify_add_group(struct fsnotify_group *group)
> {
> int priority = group->priority;
> @@ -71,13 +89,22 @@ static void fsnotify_get_group(struct fsnotify_group *group)
> atomic_inc(&group->refcnt);
> }
>
> -static void fsnotify_destroy_group(struct fsnotify_group *group)
> +void fsnotify_final_destroy_group(struct fsnotify_group *group)
> {
> if (group->ops->free_group_priv)
> group->ops->free_group_priv(group);
>
> kfree(group);
> }
missing newline
> +static void fsnotify_destroy_group(struct fsnotify_group *group)
> +{
> + /* clear all inode mark entries for this group */
> + fsnotify_clear_marks_by_group(group);
> +
> + /* past the point of no return, matches the initial value of 1 */
> + if (atomic_dec_and_test(&group->num_marks))
> + fsnotify_final_destroy_group(group);
> +}
>
>
> ...
>
> +void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry)
> +{
> + struct fsnotify_group *group;
> + struct inode *inode;
> +
> + spin_lock(&entry->lock);
> +
> + group = entry->group;
> + inode = entry->inode;
> +
> + BUG_ON(group && !inode);
> + BUG_ON(!group && inode);
> +
> + /* if !group something else already marked this to die */
> + if (!group) {
> + spin_unlock(&entry->lock);
> + return;
> + }
> +
> + /* this just tests that the caller held a reference */
> + if (unlikely(atomic_read(&entry->refcnt) < 3))
> + BUG();
BUG_ON()
> + spin_lock(&group->mark_lock);
> + spin_lock(&inode->i_lock);
> +
> + hlist_del_init(&entry->i_list);
> + entry->inode = NULL;
> + fsnotify_put_mark(entry); /* for i_list */
> +
> + list_del_init(&entry->g_list);
> + entry->group = NULL;
> + fsnotify_put_mark(entry); /* for g_list */
> +
> + fsnotify_recalc_inode_mask_locked(inode);
> +
> + spin_unlock(&inode->i_lock);
> + spin_unlock(&group->mark_lock);
> + spin_unlock(&entry->lock);
> +
> + group->ops->freeing_mark(entry, group);
> +
> + if (atomic_dec_and_test(&group->num_marks))
> + fsnotify_final_destroy_group(group);
> +}
> +
>
> ...
>
> +void fsnotify_init_mark(struct fsnotify_mark_entry *entry, void (*free_mark)(struct fsnotify_mark_entry *entry))
you must have a wide monitor.
> +
> +{
> + spin_lock_init(&entry->lock);
> + atomic_set(&entry->refcnt, 1);
> + INIT_HLIST_NODE(&entry->i_list);
> + entry->group = NULL;
> + entry->mask = 0;
> + entry->inode = NULL;
> + entry->free_mark = free_mark;
> +}
> +
>
> ...
>
--
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