Introduce a mechanism to replace a file linked in the epoll interface with a new
file.
eventpoll_replace() finds all instances of the file to be replaced and replaces
them with the new file and the interested events.
Signed-off-by: aloktiagi <aloktiagi@xxxxxxxxx>
---
Changes in v6:
- incorporate latest changes that get rid of the global epmutex lock.
Changes in v5:
- address review comments and move the call to replace old file in each
subsystem (epoll, io_uring, etc.) outside the fdtable helpers like
replace_fd().
Changes in v4:
- address review comment to remove the redundant eventpoll_replace() function.
- removed an extra empty line introduced in include/linux/file.h
Changes in v3:
- address review comment and iterate over the file table while holding the
spin_lock(&files->file_lock).
- address review comment and call filp_close() outside the
spin_lock(&files->file_lock).
---
fs/eventpoll.c | 76 +++++++++++++++++++++++++++++++++++++++
include/linux/eventpoll.h | 8 +++++
2 files changed, 84 insertions(+)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 980483455cc0..9c7bffa8401b 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -973,6 +973,82 @@ void eventpoll_release_file(struct file *file)
spin_unlock(&file->f_lock);
}
+static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
+ struct file *tfile, int fd, int full_check);
+
+/*
+ * This is called from eventpoll_replace() to replace a linked file in the epoll
+ * interface with a new file received from another process. This is useful in
+ * cases where a process is trying to install a new file for an existing one
+ * that is linked in the epoll interface
+ */
+int eventpoll_replace_file(struct file *toreplace, struct file *file, int tfd)
+{
+ struct file *to_remove = toreplace;
+ struct epoll_event event;
+ struct hlist_node *next;
+ struct eventpoll *ep;
+ struct epitem *epi;
+ int error = 0;
+ bool dispose;
+ int fd;
+
+ if (!file_can_poll(file))
+ return 0;
+
+ spin_lock(&toreplace->f_lock);
+ if (unlikely(!toreplace->f_ep)) {
+ spin_unlock(&toreplace->f_lock);
+ return 0;
+ }
+ hlist_for_each_entry_safe(epi, next, toreplace->f_ep, fllink) {
+ ep = epi->ep;
+ mutex_lock(&ep->mtx);
+ fd = epi->ffd.fd;
+ if (fd != tfd) {
+ mutex_unlock(&ep->mtx);
+ continue;
+ }
+ event = epi->event;
+ error = ep_insert(ep, &event, file, fd, 1);
+ mutex_unlock(&ep->mtx);
+ if (error != 0) {
+ break;
+ }
+ }
+ spin_unlock(&toreplace->f_lock);
+ /*
+ * In case of an error remove all instances of the new file in the epoll
+ * interface. If no error, remove all instances of the original file.
+ */
+ if (error != 0)
+ to_remove = file;
+
+again:
+ spin_lock(&to_remove->f_lock);
+ if (to_remove->f_ep && to_remove->f_ep->first) {
+ epi = hlist_entry(to_remove->f_ep->first, struct epitem, fllink);
+ fd = epi->ffd.fd;
+ if (fd != tfd) {
+ spin_unlock(&to_remove->f_lock);
+ goto again;
+ }
+ epi->dying = true;
+ spin_unlock(&to_remove->f_lock);
+
+ ep = epi->ep;
+ mutex_lock(&ep->mtx);
+ dispose = __ep_remove(ep, epi, true);
+ mutex_unlock(&ep->mtx);
+
+ if (dispose)
+ ep_free(ep);
+ goto again;
+ }
+ spin_unlock(&to_remove->f_lock);
+ return error;
+}
+
static int ep_alloc(struct eventpoll **pep)
{
int error;
diff --git a/include/linux/eventpoll.h b/include/linux/eventpoll.h
index 3337745d81bd..2a6c8f52f272 100644
--- a/include/linux/eventpoll.h
+++ b/include/linux/eventpoll.h
@@ -25,6 +25,14 @@ struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd, unsigned long t
/* Used to release the epoll bits inside the "struct file" */
void eventpoll_release_file(struct file *file);
+/*
+ * This is called from fs/file.c:do_replace() to replace a linked file in the
+ * epoll interface with a new file received from another process. This is useful
+ * in cases where a process is trying to install a new file for an existing one
+ * that is linked in the epoll interface
+ */
+int eventpoll_replace_file(struct file *toreplace, struct file *file, int tfd);
+
/*
* This is called from inside fs/file_table.c:__fput() to unlink files
* from the eventpoll interface. We need to have this facility to cleanup
--
2.34.1
