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Subject[PATCH 2/5] kernfs: add kernfs_ops->open/release() callbacks
Date
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>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/kernfs/dir.c | 2 +-
fs/kernfs/file.c | 51 +++++++++++++++++++++++++++++++++++++++------
fs/kernfs/kernfs-internal.h | 2 +-
include/linux/kernfs.h | 10 +++++++++
4 files changed, 57 insertions(+), 8 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index cf4c636..0b9d23b 100644
--- 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
--- 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 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
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
--- 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
--- 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
--
2.9.3
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