Add epoll support to bpf struct_ops links to trigger EPOLLHUP event upon
detachment.
This patch implements the "poll" of the "struct file_operations" for BPF
links and introduces a new "poll" operator in the "struct bpf_link_ops". By
implementing "poll" of "struct bpf_link_ops" for the links of struct_ops,
the file descriptor of a struct_ops link can be added to an epoll file
descriptor to receive EPOLLHUP events.
Signed-off-by: Kui-Feng Lee <thinker.li@xxxxxxxxx>
---
include/linux/bpf.h | 1 +
kernel/bpf/bpf_struct_ops.c | 17 +++++++++++++++++
kernel/bpf/syscall.c | 31 ++++++++++++++++++++++++++-----
3 files changed, 44 insertions(+), 5 deletions(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index b600767ebe02..5f7496ef8b7c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1612,6 +1612,7 @@ struct bpf_link_ops {
struct bpf_link_info *info);
int (*update_map)(struct bpf_link *link, struct bpf_map *new_map,
struct bpf_map *old_map);
+ __poll_t (*poll)(struct file *file, struct poll_table_struct *pts);
};
struct bpf_tramp_link {
diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
index f2439acd9757..855a1b2b6e79 100644
--- a/kernel/bpf/bpf_struct_ops.c
+++ b/kernel/bpf/bpf_struct_ops.c
@@ -12,6 +12,7 @@
#include <linux/mutex.h>
#include <linux/btf_ids.h>
#include <linux/rcupdate_wait.h>
+#include <linux/poll.h>
struct bpf_struct_ops_value {
struct bpf_struct_ops_common_value common;
@@ -56,6 +57,7 @@ struct bpf_struct_ops_map {
struct bpf_struct_ops_link {
struct bpf_link link;
struct bpf_map __rcu *map;
+ wait_queue_head_t wait_hup;
};
static DEFINE_MUTEX(update_mutex);
@@ -1167,15 +1169,28 @@ static int bpf_struct_ops_map_link_detach(struct bpf_link *link)
mutex_unlock(&update_mutex);
+ wake_up_interruptible_poll(&st_link->wait_hup, EPOLLHUP);
+
return 0;
}
+static __poll_t bpf_struct_ops_map_link_poll(struct file *file,
+ struct poll_table_struct *pts)
+{
+ struct bpf_struct_ops_link *st_link = file->private_data;
+
+ poll_wait(file, &st_link->wait_hup, pts);
+
+ return rcu_access_pointer(st_link->map) ? 0 : EPOLLHUP;
+}
+
static const struct bpf_link_ops bpf_struct_ops_map_lops = {
.dealloc = bpf_struct_ops_map_link_dealloc,
.detach = bpf_struct_ops_map_link_detach,
.show_fdinfo = bpf_struct_ops_map_link_show_fdinfo,
.fill_link_info = bpf_struct_ops_map_link_fill_link_info,
.update_map = bpf_struct_ops_map_link_update,
+ .poll = bpf_struct_ops_map_link_poll,
};
int bpf_struct_ops_link_create(union bpf_attr *attr)
@@ -1213,6 +1228,8 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
*/
RCU_INIT_POINTER(link->map, map);
+ init_waitqueue_head(&link->wait_hup);
+
mutex_lock(&update_mutex);
err = st_map->st_ops_desc->st_ops->reg(st_map->kvalue.data, &link->link);
if (err) {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 13ad74ecf2cd..741f91153fe6 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3150,6 +3150,13 @@ static void bpf_link_show_fdinfo(struct seq_file *m, struct file *filp)
}
#endif
+static __poll_t bpf_link_poll(struct file *file, struct poll_table_struct *pts)
+{
+ struct bpf_link *link = file->private_data;
+
+ return link->ops->poll(file, pts);
+}
+
static const struct file_operations bpf_link_fops = {
#ifdef CONFIG_PROC_FS
.show_fdinfo = bpf_link_show_fdinfo,
@@ -3159,6 +3166,16 @@ static const struct file_operations bpf_link_fops = {
.write = bpf_dummy_write,
};
+static const struct file_operations bpf_link_fops_poll = {
+#ifdef CONFIG_PROC_FS
+ .show_fdinfo = bpf_link_show_fdinfo,
+#endif
+ .release = bpf_link_release,
+ .read = bpf_dummy_read,
+ .write = bpf_dummy_write,
+ .poll = bpf_link_poll,
+};
+
static int bpf_link_alloc_id(struct bpf_link *link)
{
int id;
@@ -3201,7 +3218,9 @@ int bpf_link_prime(struct bpf_link *link, struct bpf_link_primer *primer)
return id;
}
- file = anon_inode_getfile("bpf_link", &bpf_link_fops, link, O_CLOEXEC);
+ file = anon_inode_getfile("bpf_link",
+ link->ops->poll ? &bpf_link_fops_poll : &bpf_link_fops,
+ link, O_CLOEXEC);
if (IS_ERR(file)) {
bpf_link_free_id(id);
put_unused_fd(fd);
@@ -3229,7 +3248,9 @@ int bpf_link_settle(struct bpf_link_primer *primer)
int bpf_link_new_fd(struct bpf_link *link)
{
- return anon_inode_getfd("bpf-link", &bpf_link_fops, link, O_CLOEXEC);
+ return anon_inode_getfd("bpf-link",
+ link->ops->poll ? &bpf_link_fops_poll : &bpf_link_fops,
+ link, O_CLOEXEC);
}
struct bpf_link *bpf_link_get_from_fd(u32 ufd)
@@ -3239,7 +3260,7 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd)
if (!f.file)
return ERR_PTR(-EBADF);
- if (f.file->f_op != &bpf_link_fops) {
+ if (f.file->f_op != &bpf_link_fops && f.file->f_op != &bpf_link_fops_poll) {
fdput(f);
return ERR_PTR(-EINVAL);
}
@@ -4966,7 +4987,7 @@ static int bpf_obj_get_info_by_fd(const union bpf_attr *attr,
uattr);
else if (f.file->f_op == &btf_fops)
err = bpf_btf_get_info_by_fd(f.file, f.file->private_data, attr, uattr);
- else if (f.file->f_op == &bpf_link_fops)
+ else if (f.file->f_op == &bpf_link_fops || f.file->f_op == &bpf_link_fops_poll)
err = bpf_link_get_info_by_fd(f.file, f.file->private_data,
attr, uattr);
else
@@ -5101,7 +5122,7 @@ static int bpf_task_fd_query(const union bpf_attr *attr,
if (!file)
return -EBADF;
- if (file->f_op == &bpf_link_fops) {
+ if (file->f_op == &bpf_link_fops || file->f_op == &bpf_link_fops_poll) {
struct bpf_link *link = file->private_data;
if (link->ops == &bpf_raw_tp_link_lops) {
--
2.34.1
