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Subject[PATCH v2 25/34] sysfs, kernfs: add kernfs_ops->seq_{start|next|stop}()
kernfs_ops currently only supports single_open() behavior which is
pretty restrictive. Add optional callbacks ->seq_{start|next|stop}()
which, when implemented, are invoked for seq_file traversal. This
allows full seq_file functionality for kernfs users. This currently
doesn't have any user and doesn't change any behavior.

v2: Refreshed on top of the updated "sysfs, kernfs: prepare read path
for kernfs".

Signed-off-by: Tejun Heo <tj@kernel.org>
---
fs/sysfs/file.c | 39 ++++++++++++++++++++++++++++-----------
include/linux/kernfs.h | 9 +++++++--
2 files changed, 35 insertions(+), 13 deletions(-)

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 971f1d8..9b79160 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -146,6 +146,7 @@ static ssize_t sysfs_kf_bin_read(struct sysfs_open_file *of, char *buf,
static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
{
struct sysfs_open_file *of = sf->private;
+ const struct kernfs_ops *ops;

/*
* @of->mutex nests outside active ref and is just to ensure that
@@ -157,26 +158,42 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
return ERR_PTR(-ENODEV);
}

- /*
- * The same behavior and code as single_open(). Returns !NULL if
- * pos is at the beginning; otherwise, NULL.
- */
- return NULL + !*ppos;
+ ops = kernfs_ops(of->sd);
+ if (ops->seq_start) {
+ return ops->seq_start(sf, ppos);
+ } else {
+ /*
+ * The same behavior and code as single_open(). Returns
+ * !NULL if pos is at the beginning; otherwise, NULL.
+ */
+ return NULL + !*ppos;
+ }
}

static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
{
- /*
- * The same behavior and code as single_open(), always terminate
- * after the initial read.
- */
- ++*ppos;
- return NULL;
+ struct sysfs_open_file *of = sf->private;
+ const struct kernfs_ops *ops = kernfs_ops(of->sd);
+
+ if (ops->seq_next) {
+ return ops->seq_next(sf, v, ppos);
+ } else {
+ /*
+ * The same behavior and code as single_open(), always
+ * terminate after the initial read.
+ */
+ ++*ppos;
+ return NULL;
+ }
}

static void kernfs_seq_stop(struct seq_file *sf, void *v)
{
struct sysfs_open_file *of = sf->private;
+ const struct kernfs_ops *ops = kernfs_ops(of->sd);
+
+ if (ops->seq_stop)
+ ops->seq_stop(sf, v);

sysfs_put_active(of->sd);
mutex_unlock(&of->mutex);
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index a1b94b7..222040c 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -36,8 +36,9 @@ struct kernfs_ops {
/*
* Read is handled by either seq_file or raw_read().
*
- * If seq_show() is present, seq_file path is active. The behavior
- * is equivalent to single_open(). @sf->private points to the
+ * If seq_show() is present, seq_file path is active. Other seq
+ * operations are optional and if not implemented, the behavior is
+ * equivalent to single_open(). @sf->private points to the
* associated sysfs_open_file.
*
* read() is bounced through kernel buffer and a read larger than
@@ -45,6 +46,10 @@ struct kernfs_ops {
*/
int (*seq_show)(struct seq_file *sf, void *v);

+ void *(*seq_start)(struct seq_file *sf, loff_t *ppos);
+ void *(*seq_next)(struct seq_file *sf, void *v, loff_t *ppos);
+ void (*seq_stop)(struct seq_file *sf, void *v);
+
ssize_t (*read)(struct sysfs_open_file *of, char *buf, size_t bytes,
loff_t off);

--
1.8.3.1


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