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    Subject[RFC 02/20] timens: Add timens_offsets
    Date
    From: Andrei Vagin <avagin@openvz.org>

    Introduce offsets for time namespace. They will contain adjustment
    needed to convert clocks to/from host's.

    Allocate one page for each time namespace that will be premapped into
    userspace with vvar pages.

    Signed-off-by: Andrei Vagin <avagin@openvz.org>
    Signed-off-by: Dmitry Safonov <dima@arista.com>
    ---
    include/linux/time_namespace.h | 2 ++
    include/linux/timens_offsets.h | 8 ++++++++
    kernel/time_namespace.c | 14 ++++++++++++--
    3 files changed, 22 insertions(+), 2 deletions(-)
    create mode 100644 include/linux/timens_offsets.h

    diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
    index bf98f35efe07..4960c54f1b33 100644
    --- a/include/linux/time_namespace.h
    +++ b/include/linux/time_namespace.h
    @@ -8,6 +8,7 @@
    #include <linux/nsproxy.h>
    #include <linux/ns_common.h>
    #include <linux/err.h>
    +#include <linux/timens_offsets.h>

    struct user_namespace;
    extern struct user_namespace init_user_ns;
    @@ -17,6 +18,7 @@ struct time_namespace {
    struct user_namespace *user_ns;
    struct ucounts *ucounts;
    struct ns_common ns;
    + struct timens_offsets *offsets;
    } __randomize_layout;
    extern struct time_namespace init_time_ns;

    diff --git a/include/linux/timens_offsets.h b/include/linux/timens_offsets.h
    new file mode 100644
    index 000000000000..7d7cb68ea778
    --- /dev/null
    +++ b/include/linux/timens_offsets.h
    @@ -0,0 +1,8 @@
    +/* SPDX-License-Identifier: GPL-2.0 */
    +#ifndef _LINUX_TIME_OFFSETS_H
    +#define _LINUX_TIME_OFFSETS_H
    +
    +struct timens_offsets {
    +};
    +
    +#endif
    diff --git a/kernel/time_namespace.c b/kernel/time_namespace.c
    index 902cd9c22159..a985529754b4 100644
    --- a/kernel/time_namespace.c
    +++ b/kernel/time_namespace.c
    @@ -13,6 +13,7 @@
    #include <linux/user_namespace.h>
    #include <linux/proc_ns.h>
    #include <linux/sched/task.h>
    +#include <linux/mm.h>

    static struct ucounts *inc_time_namespaces(struct user_namespace *ns)
    {
    @@ -44,6 +45,7 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
    {
    struct time_namespace *ns;
    struct ucounts *ucounts;
    + struct page *page;
    int err;

    err = -ENOSPC;
    @@ -56,15 +58,22 @@ static struct time_namespace *clone_time_ns(struct user_namespace *user_ns,
    if (!ns)
    goto fail_dec;

    + page = alloc_page(GFP_KERNEL | __GFP_ZERO);
    + if (!page)
    + goto fail_free;
    + ns->offsets = page_address(page);
    + BUILD_BUG_ON(sizeof(*ns->offsets) > PAGE_SIZE);
    +
    err = ns_alloc_inum(&ns->ns);
    if (err)
    - goto fail_free;
    + goto fail_page;

    ns->ucounts = ucounts;
    ns->ns.ops = &timens_operations;
    ns->user_ns = get_user_ns(user_ns);
    return ns;
    -
    +fail_page:
    + free_page((unsigned long)ns->offsets);
    fail_free:
    kfree(ns);
    fail_dec:
    @@ -93,6 +102,7 @@ void free_time_ns(struct kref *kref)
    struct time_namespace *ns;

    ns = container_of(kref, struct time_namespace, kref);
    + free_page((unsigned long)ns->offsets);
    dec_time_namespaces(ns->ucounts);
    put_user_ns(ns->user_ns);
    ns_free_inum(&ns->ns);
    --
    2.13.6
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