kernfs: add kernfs_ops->open/release() callbacks

Add ->open/release() methods to kernfs_ops.  ->open() is called when
the file is opened and ->release() when the file is either released or
severed.  These callbacks can be used, for example, to manage
persistent caching objects over multiple seq_file iterations.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Acked-by: Zefan Li <lizefan@huawei.com>

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index cf4c636..0b9d23b 100644 (file)
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -468,7 +468,7 @@ static void kernfs_drain(struct kernfs_node *kn)
                rwsem_release(&kn->dep_map, 1, _RET_IP_);
        }
 
-       kernfs_unmap_bin_file(kn);
+       kernfs_drain_open_files(kn);
 
        mutex_lock(&kernfs_mutex);
 }

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index d0b6fb1..20c3962 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -708,7 +708,8 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
        if (error)
                goto err_free;
 
-       ((struct seq_file *)file->private_data)->private = of;
+       of->seq_file = file->private_data;
+       of->seq_file->private = of;
 
        /* seq_file clears PWRITE unconditionally, restore it if WRITE */
        if (file->f_mode & FMODE_WRITE)
@@ -717,13 +718,22 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
        /* make sure we have open node struct */
        error = kernfs_get_open_node(kn, of);
        if (error)
-               goto err_close;
+               goto err_seq_release;
+
+       if (ops->open) {
+               /* nobody has access to @of yet, skip @of->mutex */
+               error = ops->open(of);
+               if (error)
+                       goto err_put_node;
+       }
 
        /* open succeeded, put active references */
        kernfs_put_active(kn);
        return 0;
 
-err_close:
+err_put_node:
+       kernfs_put_open_node(kn, of);
+err_seq_release:
        seq_release(inode, file);
 err_free:
        kfree(of->prealloc_buf);
@@ -733,11 +743,32 @@ err_out:
        return error;
 }
 
+/* used from release/drain to ensure that ->release() is called exactly once */
+static void kernfs_release_file(struct kernfs_node *kn,
+                               struct kernfs_open_file *of)
+{
+       if (!(kn->flags & KERNFS_HAS_RELEASE))
+               return;
+
+       mutex_lock(&of->mutex);
+       if (!of->released) {
+               /*
+                * A file is never detached without being released and we
+                * need to be able to release files which are deactivated
+                * and being drained.  Don't use kernfs_ops().
+                */
+               kn->attr.ops->release(of);
+               of->released = true;
+       }
+       mutex_unlock(&of->mutex);
+}
+
 static int kernfs_fop_release(struct inode *inode, struct file *filp)
 {
        struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
        struct kernfs_open_file *of = kernfs_of(filp);
 
+       kernfs_release_file(kn, of);
        kernfs_put_open_node(kn, of);
        seq_release(inode, filp);
        kfree(of->prealloc_buf);
@@ -746,12 +777,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
        return 0;
 }
 
-void kernfs_unmap_bin_file(struct kernfs_node *kn)
+void kernfs_drain_open_files(struct kernfs_node *kn)
 {
        struct kernfs_open_node *on;
        struct kernfs_open_file *of;
 
-       if (!(kn->flags & KERNFS_HAS_MMAP))
+       if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
                return;
 
        spin_lock_irq(&kernfs_open_node_lock);
@@ -763,10 +794,16 @@ void kernfs_unmap_bin_file(struct kernfs_node *kn)
                return;
 
        mutex_lock(&kernfs_open_file_mutex);
+
        list_for_each_entry(of, &on->files, list) {
                struct inode *inode = file_inode(of->file);
-               unmap_mapping_range(inode->i_mapping, 0, 0, 1);
+
+               if (kn->flags & KERNFS_HAS_MMAP)
+                       unmap_mapping_range(inode->i_mapping, 0, 0, 1);
+
+               kernfs_release_file(kn, of);
        }
+
        mutex_unlock(&kernfs_open_file_mutex);
 
        kernfs_put_open_node(kn, NULL);
@@ -965,6 +1002,8 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
                kn->flags |= KERNFS_HAS_SEQ_SHOW;
        if (ops->mmap)
                kn->flags |= KERNFS_HAS_MMAP;
+       if (ops->release)
+               kn->flags |= KERNFS_HAS_RELEASE;
 
        rc = kernfs_add_one(kn);
        if (rc) {

diff --git a/fs/kernfs/kernfs-internal.h b/fs/kernfs/kernfs-internal.h
index bfd551b..3100987 100644 (file)
--- a/fs/kernfs/kernfs-internal.h
+++ b/fs/kernfs/kernfs-internal.h
@@ -104,7 +104,7 @@ struct kernfs_node *kernfs_new_node(struct kernfs_node *parent,
  */
 extern const struct file_operations kernfs_file_fops;
 
-void kernfs_unmap_bin_file(struct kernfs_node *kn);
+void kernfs_drain_open_files(struct kernfs_node *kn);
 
 /*
  * symlink.c

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index afd4e5a..a9b11b8 100644 (file)
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -46,6 +46,7 @@ enum kernfs_node_flag {
        KERNFS_SUICIDAL         = 0x0400,
        KERNFS_SUICIDED         = 0x0800,
        KERNFS_EMPTY_DIR        = 0x1000,
+       KERNFS_HAS_RELEASE      = 0x2000,
 };
 
 /* @flags for kernfs_create_root() */
@@ -175,6 +176,7 @@ struct kernfs_open_file {
        /* published fields */
        struct kernfs_node      *kn;
        struct file             *file;
+       struct seq_file         *seq_file;
        void                    *priv;
 
        /* private fields, do not use outside kernfs proper */
@@ -186,11 +188,19 @@ struct kernfs_open_file {
 
        size_t                  atomic_write_len;
        bool                    mmapped:1;
+       bool                    released:1;
        const struct vm_operations_struct *vm_ops;
 };
 
 struct kernfs_ops {
        /*
+        * Optional open/release methods.  Both are called with
+        * @of->seq_file populated.
+        */
+       int (*open)(struct kernfs_open_file *of);
+       void (*release)(struct kernfs_open_file *of);
+
+       /*
         * Read is handled by either seq_file or raw_read().
         *
         * If seq_show() is present, seq_file path is active.  Other seq