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    Subject[PATCH 2/4] input: evdev: Use multi-reader buffer to save space (rev3)
    Date
    Preparing for larger buffer needs, convert the current per-client
    circular buffer to a single buffer with multiple clients. Use the
    buflock mechanism, where clients wait during buffer collision only.

    Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
    ---
    drivers/input/evdev.c | 57 ++++++++++++++++++++++++-------------------------
    1 files changed, 28 insertions(+), 29 deletions(-)

    diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
    index 2ee6c7a..7f0c7da 100644
    --- a/drivers/input/evdev.c
    +++ b/drivers/input/evdev.c
    @@ -21,6 +21,7 @@
    #include <linux/major.h>
    #include <linux/device.h>
    #include "input-compat.h"
    +#include "buflock.h"

    struct evdev {
    int exist;
    @@ -33,13 +34,13 @@ struct evdev {
    spinlock_t client_lock; /* protects client_list */
    struct mutex mutex;
    struct device dev;
    + struct buflock_writer writer;
    + struct input_event buffer[EVDEV_BUFFER_SIZE];
    };

    struct evdev_client {
    - struct input_event buffer[EVDEV_BUFFER_SIZE];
    - int head;
    - int tail;
    - spinlock_t buffer_lock; /* protects access to buffer, head and tail */
    + struct buflock_reader reader;
    + spinlock_t entry_lock; /* protects reentrant fops reads */
    struct fasync_struct *fasync;
    struct evdev *evdev;
    struct list_head node;
    @@ -48,18 +49,12 @@ struct evdev_client {
    static struct evdev *evdev_table[EVDEV_MINORS];
    static DEFINE_MUTEX(evdev_table_mutex);

    -static void evdev_pass_event(struct evdev_client *client,
    - struct input_event *event)
    +static inline void evdev_sync_event(struct evdev_client *client,
    + struct evdev *evdev, int type)
    {
    - /*
    - * Interrupts are disabled, just acquire the lock
    - */
    - spin_lock(&client->buffer_lock);
    - client->buffer[client->head++] = *event;
    - client->head &= EVDEV_BUFFER_SIZE - 1;
    - spin_unlock(&client->buffer_lock);
    -
    - if (event->type == EV_SYN)
    + /* sync reader, no locks required */
    + buflock_sync_reader(client->reader, evdev->writer);
    + if (type == EV_SYN)
    kill_fasync(&client->fasync, SIGIO, POLL_IN);
    }

    @@ -78,14 +73,17 @@ static void evdev_event(struct input_handle *handle,
    event.code = code;
    event.value = value;

    + /* lock-less write */
    + buflock_write(evdev->writer, evdev->buffer, EVDEV_BUFFER_SIZE, event);
    +
    rcu_read_lock();

    client = rcu_dereference(evdev->grab);
    if (client)
    - evdev_pass_event(client, &event);
    + evdev_sync_event(client, evdev, type);
    else
    list_for_each_entry_rcu(client, &evdev->client_list, node)
    - evdev_pass_event(client, &event);
    + evdev_sync_event(client, evdev, type);

    rcu_read_unlock();

    @@ -269,7 +267,7 @@ static int evdev_open(struct inode *inode, struct file *file)
    goto err_put_evdev;
    }

    - spin_lock_init(&client->buffer_lock);
    + spin_lock_init(&client->entry_lock);
    client->evdev = evdev;
    evdev_attach_client(evdev, client);

    @@ -325,19 +323,19 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer,
    }

    static int evdev_fetch_next_event(struct evdev_client *client,
    + struct evdev *evdev,
    struct input_event *event)
    {
    int have_event;

    - spin_lock_irq(&client->buffer_lock);
    + spin_lock_irq(&client->entry_lock);

    - have_event = client->head != client->tail;
    - if (have_event) {
    - *event = client->buffer[client->tail++];
    - client->tail &= EVDEV_BUFFER_SIZE - 1;
    - }
    + have_event = !buflock_reader_empty(client->reader);
    + if (have_event)
    + buflock_read(client->reader, evdev->writer,
    + evdev->buffer, EVDEV_BUFFER_SIZE, *event);

    - spin_unlock_irq(&client->buffer_lock);
    + spin_unlock_irq(&client->entry_lock);

    return have_event;
    }
    @@ -353,12 +351,12 @@ static ssize_t evdev_read(struct file *file, char __user *buffer,
    if (count < input_event_size())
    return -EINVAL;

    - if (client->head == client->tail && evdev->exist &&
    + if (buflock_reader_empty(client->reader) && evdev->exist &&
    (file->f_flags & O_NONBLOCK))
    return -EAGAIN;

    retval = wait_event_interruptible(evdev->wait,
    - client->head != client->tail || !evdev->exist);
    + !buflock_reader_empty(client->reader) || !evdev->exist);
    if (retval)
    return retval;

    @@ -366,7 +364,7 @@ static ssize_t evdev_read(struct file *file, char __user *buffer,
    return -ENODEV;

    while (retval + input_event_size() <= count &&
    - evdev_fetch_next_event(client, &event)) {
    + evdev_fetch_next_event(client, evdev, &event)) {

    if (input_event_to_user(buffer + retval, &event))
    return -EFAULT;
    @@ -384,7 +382,8 @@ static unsigned int evdev_poll(struct file *file, poll_table *wait)
    struct evdev *evdev = client->evdev;

    poll_wait(file, &evdev->wait, wait);
    - return ((client->head == client->tail) ? 0 : (POLLIN | POLLRDNORM)) |
    + return (buflock_reader_empty(client->reader) ? 0 :
    + (POLLIN | POLLRDNORM)) |
    (evdev->exist ? 0 : (POLLHUP | POLLERR));
    }

    --
    1.6.3.3


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