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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 28 insertions, 11 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 9852450867cf..74e3478d9cb4 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
@@ -155,26 +156,42 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
         if (!sysfs_get_active(of->sd))
                 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);