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    Subject[PATCH v4 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 50bb99e98872..90dc75ad4144 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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