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bpf: support epoll from bpf struct_ops links.

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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@gmail.com>
Link: https://lore.kernel.org/r/20240530065946.979330-4-thinker.li@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
This commit is contained in:
Kui-Feng Lee 2024-05-29 23:59:41 -07:00 committed by Martin KaFai Lau
parent 6fb2544ea1
commit 1adddc97aa
3 changed files with 44 additions and 5 deletions
include/linux
bpf.h
kernel/bpf
bpf_struct_ops.csyscall.c

1
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 {

17
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)
@ -1208,6 +1223,8 @@ int bpf_struct_ops_link_create(union bpf_attr *attr)
if (err)
goto err_out;
init_waitqueue_head(&link->wait_hup);
/* Hold the update_mutex such that the subsystem cannot
* do link->ops->detach() before the link is fully initialized.
*/

31
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);
}
@ -4971,7 +4992,7 @@ 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
@ -5106,7 +5127,7 @@ 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) {