eventpoll: add file based control interface

Add do_epoll_ctl_file(), which takes a pre-resolved epoll file and a
struct epoll_filefd for the target rather than two integer file
descriptors. do_epoll_ctl() remains as a thin wrapper.

In preparation for using the file based interface from io_uring.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Link: https://patch.msgid.link/20260514140817.623026-4-axboe@kernel.dk
Signed-off-by: Christian Brauner <brauner@kernel.org>

2 files changed, 39 insertions, 30 deletions

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 9ea6a2bd3d87..1c7001866340 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -99,11 +99,6 @@
 
 #define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))
 
-struct epoll_filefd {
-	struct file *file;
-	int fd;
-} __packed;
-
 /* Wait structure used by the poll hooks */
 struct eppoll_entry {
 	/* List header used to link this structure to the "struct epitem" */
@@ -2225,30 +2220,17 @@ static inline int epoll_mutex_lock(struct mutex *mutex, int depth,
 	return -EAGAIN;
 }
 
-int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
-		 bool nonblock)
+int do_epoll_ctl_file(struct file *f, int op, struct epoll_filefd *tf,
+		      struct epoll_event *epds, bool nonblock)
 {
 	int error;
 	int full_check = 0;
 	struct eventpoll *ep;
 	struct epitem *epi;
 	struct eventpoll *tep = NULL;
-	struct epoll_filefd efd;
-
-	CLASS(fd, f)(epfd);
-	if (fd_empty(f))
-		return -EBADF;
-
-	/* Get the "struct file *" for the target file */
-	CLASS(fd, tf)(fd);
-	if (fd_empty(tf))
-		return -EBADF;
-
-	efd.file = fd_file(tf);
-	efd.fd = fd;
 
 	/* The target file descriptor must support poll */
-	if (!file_can_poll(fd_file(tf)))
+	if (!file_can_poll(tf->file))
 		return -EPERM;
 
 	/* Check if EPOLLWAKEUP is allowed */
@@ -2261,7 +2243,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	 * adding an epoll file descriptor inside itself.
 	 */
 	error = -EINVAL;
-	if (fd_file(f) == fd_file(tf) || !is_file_epoll(fd_file(f)))
+	if (f == tf->file || !is_file_epoll(f))
 		goto error_tgt_fput;
 
 	/*
@@ -2272,7 +2254,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	if (ep_op_has_event(op) && (epds->events & EPOLLEXCLUSIVE)) {
 		if (op == EPOLL_CTL_MOD)
 			goto error_tgt_fput;
-		if (op == EPOLL_CTL_ADD && (is_file_epoll(fd_file(tf)) ||
+		if (op == EPOLL_CTL_ADD && (is_file_epoll(tf->file) ||
 				(epds->events & ~EPOLLEXCLUSIVE_OK_BITS)))
 			goto error_tgt_fput;
 	}
@@ -2281,7 +2263,7 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	 * At this point it is safe to assume that the "private_data" contains
 	 * our own data structure.
 	 */
-	ep = fd_file(f)->private_data;
+	ep = f->private_data;
 
 	/*
 	 * When we insert an epoll file descriptor inside another epoll file
@@ -2302,16 +2284,16 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	if (error)
 		goto error_tgt_fput;
 	if (op == EPOLL_CTL_ADD) {
-		if (READ_ONCE(fd_file(f)->f_ep) || ep->gen == loop_check_gen ||
-		    is_file_epoll(fd_file(tf))) {
+		if (READ_ONCE(f->f_ep) || ep->gen == loop_check_gen ||
+		    is_file_epoll(tf->file)) {
 			mutex_unlock(&ep->mtx);
 			error = epoll_mutex_lock(&epnested_mutex, 0, nonblock);
 			if (error)
 				goto error_tgt_fput;
 			loop_check_gen++;
 			full_check = 1;
-			if (is_file_epoll(fd_file(tf))) {
-				tep = fd_file(tf)->private_data;
+			if (is_file_epoll(tf->file)) {
+				tep = tf->file->private_data;
 				error = -ELOOP;
 				if (ep_loop_check(ep, tep) != 0)
 					goto error_tgt_fput;
@@ -2327,14 +2309,14 @@ int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 	 * above, we can be sure to be able to use the item looked up by
 	 * ep_find() till we release the mutex.
 	 */
-	epi = ep_find(ep, &efd);
+	epi = ep_find(ep, tf);
 
 	error = -EINVAL;
 	switch (op) {
 	case EPOLL_CTL_ADD:
 		if (!epi) {
 			epds->events |= EPOLLERR | EPOLLHUP;
-			error = ep_insert(ep, epds, &efd, full_check);
+			error = ep_insert(ep, epds, tf, full_check);
 		} else
 			error = -EEXIST;
 		break;
@@ -2369,6 +2351,26 @@ error_tgt_fput:
 		mutex_unlock(&epnested_mutex);
 	}
 	return error;
+
+}
+
+int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
+		 bool nonblock)
+{
+	struct epoll_filefd efd;
+
+	CLASS(fd, f)(epfd);
+	if (fd_empty(f))
+		return -EBADF;
+
+	/* Get the "struct file *" for the target file */
+	CLASS(fd, tf)(fd);
+	if (fd_empty(tf))
+		return -EBADF;
+
+	efd.file = fd_file(tf);
+	efd.fd = fd;
+	return do_epoll_ctl_file(fd_file(f), op, &efd, epds, nonblock);
 }
 
 /*
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 7bf30e9f90d7..4a6fe989810b 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -61,6 +61,13 @@ static inline void eventpoll_release(struct file *file)
 	eventpoll_release_file(file);
 }
 
+struct epoll_filefd {
+	struct file *file;
+	int fd;
+} __packed;
+
+int do_epoll_ctl_file(struct file *f, int op, struct epoll_filefd *tf,
+		      struct epoll_event *epds, bool nonblock);
 int do_epoll_ctl(int epfd, int op, int fd, struct epoll_event *epds,
 		 bool nonblock);
 int is_file_epoll(struct file *f);