[PATCH 1/6] fs: kernfs: add poll file operation

Suren Baghdasaryan
2018-12-14T17:16:15Z

From: Johannes Weiner <hannes@cmpxchg.org>

Kernfs has a standardized poll/notification mechanism for waking all
pollers on all fds when a filesystem node changes. To allow polling
for custom events, add a .poll callback that can override the default.

This is in preparation for pollable cgroup pressure files which have
per-fd trigger configurations.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
fs/kernfs/file.c | 31 ++++++++++++++++++++-----------
include/linux/kernfs.h | 6 ++++++
2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index dbf5bc250bfd..2d8b91f4475d 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -832,26 +832,35 @@ void kernfs_drain_open_files(struct kernfs_node *kn)
* to see if it supports poll (Neither 'poll' nor 'select' return
* an appropriate error code). When in doubt, set a suitable timeout value.
*/
+__poll_t kernfs_generic_poll(struct kernfs_open_file *of, poll_table *wait)
+{
+ struct kernfs_node *kn = kernfs_dentry_node(of->file->f_path.dentry);
+ struct kernfs_open_node *on = kn->attr.open;
+
+ poll_wait(of->file, &on->poll, wait);
+
+ if (of->event != atomic_read(&on->event))
+ return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
+
+ return DEFAULT_POLLMASK;
+}
+
static __poll_t kernfs_fop_poll(struct file *filp, poll_table *wait)
{
struct kernfs_open_file *of = kernfs_of(filp);
struct kernfs_node *kn = kernfs_dentry_node(filp->f_path.dentry);
- struct kernfs_open_node *on = kn->attr.open;
+ __poll_t ret;

if (!kernfs_get_active(kn))
- goto trigger;
+ return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;

- poll_wait(filp, &on->poll, wait);
+ if (kn->attr.ops->poll)
+ ret = kn->attr.ops->poll(of, wait);
+ else
+ ret = kernfs_generic_poll(of, wait);

kernfs_put_active(kn);
-
- if (of->event != atomic_read(&on->event))
- goto trigger;
-
- return DEFAULT_POLLMASK;
-
- trigger:
- return DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
+ return ret;
}

static void kernfs_notify_workfn(struct work_struct *work)
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 5b36b1287a5a..0cac1207bb00 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -25,6 +25,7 @@ struct seq_file;
struct vm_area_struct;
struct super_block;
struct file_system_type;
+struct poll_table_struct;

struct kernfs_open_node;
struct kernfs_iattrs;
@@ -261,6 +262,9 @@ struct kernfs_ops {
ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
loff_t off);

+ __poll_t (*poll)(struct kernfs_open_file *of,
+ struct poll_table_struct *pt);
+
int (*mmap)(struct kernfs_open_file *of, struct vm_area_struct *vma);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
@@ -350,6 +354,8 @@ int kernfs_remove_by_name_ns(struct kernfs_node *parent, const char *name,
int kernfs_rename_ns(struct kernfs_node *kn, struct kernfs_node *new_parent,
const char *new_name, const void *new_ns);
int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr);
+__poll_t kernfs_generic_poll(struct kernfs_open_file *of,
+ struct poll_table_struct *pt);
void kernfs_notify(struct kernfs_node *kn);

const void *kernfs_super_ns(struct super_block *sb);
--
2.20.0.405.gbc1bbc6f85-goog