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    Subject[PATCH =-v3 13/21] fanotify: ability for userspace to delay responses
    Date
    Userspace may know that it is behind, may know it is going to take a while
    to get a good response, or have any number of other reasons to block an
    access request. FAN_RESTTIMER will reset the timeout for an fanotify
    access decision response.

    Signed-off-by: Eric Paris <eparis@redhat.com>
    ---

    fs/notify/access.c | 31 +++++++++++++++++++++++++++----
    fs/notify/fanotify.h | 1 +
    fs/notify/notification.c | 2 ++
    include/linux/fanotify.h | 1 +
    4 files changed, 31 insertions(+), 4 deletions(-)

    diff --git a/fs/notify/access.c b/fs/notify/access.c
    index 6a2606c..5b3b32e 100644
    --- a/fs/notify/access.c
    +++ b/fs/notify/access.c
    @@ -55,6 +55,8 @@ int fanotify_add_event_to_access(struct fanotify_group *group, struct fanotify_e
    int fanotify_get_response_from_access(struct fanotify_group *group, struct fanotify_event *event)
    {
    int ret;
    +
    +retry:
    ret = wait_event_interruptible_timeout(group->access_waitq,
    event->response,
    msecs_to_jiffies(5000));
    @@ -89,13 +91,25 @@ int fanotify_get_response_from_access(struct fanotify_group *group, struct fanot
    }

    /* userspace responded, convert to something usable */
    + spin_lock(&event->response_lock);
    switch (event->response) {
    case FAN_ALLOW:
    - return 0;
    + ret = 0;
    + break;
    case FAN_DENY:
    + ret = -EPERM;
    + break;
    + case FAN_RESETTIMER:
    + event->response = 0;
    + spin_unlock(&event->response_lock);
    + goto retry;
    default:
    - return -EPERM;
    + ret = -EPERM;
    + break;
    }
    + spin_unlock(&event->response_lock);
    +
    + return ret;
    }

    int fanotify_process_access_response(struct fanotify_group *group, unsigned long cookie, unsigned int response)
    @@ -108,7 +122,7 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
    * userspace can send a valid responce or we will clean it up after the
    * timeout
    */
    - if (response & ~(FAN_ALLOW | FAN_DENY))
    + if (response & ~(FAN_ALLOW | FAN_DENY | FAN_RESETTIMER))
    return -EINVAL;

    mutex_lock(&group->access_mutex);
    @@ -117,6 +131,11 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
    continue;

    event = holder->event;
    +
    + /* FAN_RESETTIMER should be left on the list for later.... */
    + if (response == FAN_RESETTIMER)
    + break;
    +
    spin_lock(&event->holder_spinlock);
    holder->event = NULL;
    /* as soon as we do this the event.holder might be reused */
    @@ -132,9 +151,13 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
    if (!event)
    return -ENOENT;

    + spin_lock(&event->response_lock);
    event->response = response;
    + spin_unlock(&event->response_lock);
    wake_up(&group->access_waitq);
    - fanotify_put_event(event);
    +
    + if (response != FAN_RESETTIMER)
    + fanotify_put_event(event);

    return 0;
    }
    diff --git a/fs/notify/fanotify.h b/fs/notify/fanotify.h
    index 6423af1..4f42a1f 100644
    --- a/fs/notify/fanotify.h
    +++ b/fs/notify/fanotify.h
    @@ -48,6 +48,7 @@ struct fanotify_event {
    atomic_t refcnt; /* how many groups still are using/need to send this event */
    /* if waiting for a userspace access answer this is the cookie they will send back */
    unsigned long cookie;
    + spinlock_t response_lock; /* protects response */
    unsigned int response; /* userspace answer to question */
    };

    diff --git a/fs/notify/notification.c b/fs/notify/notification.c
    index 89bb02c..dd0d2db 100644
    --- a/fs/notify/notification.c
    +++ b/fs/notify/notification.c
    @@ -27,6 +27,7 @@
    #include <linux/path.h>
    #include <linux/sched.h>
    #include <linux/slab.h>
    +#include <linux/spinlock.h>

    #include <linux/fanotify.h>
    #include "fanotify.h"
    @@ -169,6 +170,7 @@ struct fanotify_event *create_event(struct file *file, unsigned int mask)
    event->holder.event = NULL;
    INIT_LIST_HEAD(&event->holder.event_list);
    atomic_set(&event->refcnt, 1);
    + spin_lock_init(&event->response_lock);

    spin_lock_init(&event->holder_spinlock);

    diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
    index 7bc15ec..b01309e 100644
    --- a/include/linux/fanotify.h
    +++ b/include/linux/fanotify.h
    @@ -49,6 +49,7 @@
    /* answers will need to be either allow or deny */
    #define FAN_ALLOW 0x00000001
    #define FAN_DENY 0x00000002
    +#define FAN_RESETTIMER 0x00000004

    #include <linux/types.h>



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