From: Johannes Weiner <hannes@xxxxxxxxxxx> Subject: kernel: cgroup: add poll file operation Cgroup 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. Link: http://lkml.kernel.org/r/20190124211518.244221-3-surenb@xxxxxxxxxx Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Cc: Dennis Zhou <dennis@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: Li Zefan <lizefan@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/cgroup-defs.h | 4 ++++ kernel/cgroup/cgroup.c | 12 ++++++++++++ 2 files changed, 16 insertions(+) --- a/include/linux/cgroup-defs.h~kernel-cgroup-add-poll-file-operation +++ a/include/linux/cgroup-defs.h @@ -32,6 +32,7 @@ struct kernfs_node; struct kernfs_ops; struct kernfs_open_file; struct seq_file; +struct poll_table_struct; #define MAX_CGROUP_TYPE_NAMELEN 32 #define MAX_CGROUP_ROOT_NAMELEN 64 @@ -574,6 +575,9 @@ struct cftype { ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off); + __poll_t (*poll)(struct kernfs_open_file *of, + struct poll_table_struct *pt); + #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lock_class_key lockdep_key; #endif --- a/kernel/cgroup/cgroup.c~kernel-cgroup-add-poll-file-operation +++ a/kernel/cgroup/cgroup.c @@ -3534,6 +3534,16 @@ static ssize_t cgroup_file_write(struct return ret ?: nbytes; } +static __poll_t cgroup_file_poll(struct kernfs_open_file *of, poll_table *pt) +{ + struct cftype *cft = of->kn->priv; + + if (cft->poll) + return cft->poll(of, pt); + + return kernfs_generic_poll(of, pt); +} + static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos) { return seq_cft(seq)->seq_start(seq, ppos); @@ -3572,6 +3582,7 @@ static struct kernfs_ops cgroup_kf_singl .open = cgroup_file_open, .release = cgroup_file_release, .write = cgroup_file_write, + .poll = cgroup_file_poll, .seq_show = cgroup_seqfile_show, }; @@ -3580,6 +3591,7 @@ static struct kernfs_ops cgroup_kf_ops = .open = cgroup_file_open, .release = cgroup_file_release, .write = cgroup_file_write, + .poll = cgroup_file_poll, .seq_start = cgroup_seqfile_start, .seq_next = cgroup_seqfile_next, .seq_stop = cgroup_seqfile_stop, _
