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Subject[PATCH v5 02/14] epoll: introduce user structures for polling from userspace
Date
This one introduces structures of user items array:

struct epoll_uheader -
describes inserted epoll items.

struct epoll_uitem -
single epoll item visible to userspace.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
fs/eventpoll.c | 11 +++++++++++
include/uapi/linux/eventpoll.h | 29 +++++++++++++++++++++++++++++
2 files changed, 40 insertions(+)

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 622b6c9ef8c9..6d7a5fe4a831 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -4,6 +4,7 @@
* Copyright (C) 2001,...,2009 Davide Libenzi
*
* Davide Libenzi <davidel@xmailserver.org>
+ * Polling from userspace support by Roman Penyaev <rpenyaev@suse.de>
*/

#include <linux/init.h>
@@ -104,6 +105,16 @@

#define EP_ITEM_COST (sizeof(struct epitem) + sizeof(struct eppoll_entry))

+/*
+ * That is around 1.3mb of allocated memory for one epfd. What is more
+ * important is ->index_length, which should be ^2, so do not increase
+ * max items number to avoid size doubling of user index.
+ *
+ * Before increasing the value see add_event_to_uring() and especially
+ * cnt_to_advance() functions and change them accordingly.
+ */
+#define EP_USERPOLL_MAX_ITEMS_NR 65536
+
struct epoll_filefd {
struct file *file;
int fd;
diff --git a/include/uapi/linux/eventpoll.h b/include/uapi/linux/eventpoll.h
index 39dfc29f0f52..3317901b19c4 100644
--- a/include/uapi/linux/eventpoll.h
+++ b/include/uapi/linux/eventpoll.h
@@ -79,4 +79,33 @@ struct epoll_event {
__u64 data;
} EPOLL_PACKED;

+#define EPOLL_USERPOLL_HEADER_MAGIC 0xeb01eb01
+#define EPOLL_USERPOLL_HEADER_SIZE 128
+
+/*
+ * Item, shared with userspace. Unfortunately we can't embed epoll_event
+ * structure, because it is badly aligned on all 64-bit archs, except
+ * x86-64 (see EPOLL_PACKED). sizeof(epoll_uitem) == 16
+ */
+struct epoll_uitem {
+ __poll_t ready_events;
+ __poll_t events;
+ __u64 data;
+};
+
+/*
+ * Header, shared with userspace. sizeof(epoll_uheader) == 128
+ */
+struct epoll_uheader {
+ __u32 magic; /* epoll user header magic */
+ __u32 header_length; /* length of the header + items */
+ __u32 index_length; /* length of the index ring, always pow2 */
+ __u32 max_items_nr; /* max number of items */
+ __u32 head; /* updated by userland */
+ __u32 tail; /* updated by kernel */
+
+ struct epoll_uitem items[]
+ __attribute__((__aligned__(EPOLL_USERPOLL_HEADER_SIZE)));
+};
+
#endif /* _UAPI_LINUX_EVENTPOLL_H */
--
2.21.0
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