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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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