tty: Enable configurable tty flip buffer limit

Allow driver to configure its maximum flip buffer memory
consumption/limit. This is necessary for very-high speed line
rates (in excess of 10MB/sec) because the flip buffers can
be saturated before the line discipline has a chance to
throttle the input.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index c043136fbe5198cf0a7a8704254fc28763ecd0b9..57eb34b2ec24760659b53c2a2503baef162ef4ca 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -26,7 +26,7 @@
  * Byte threshold to limit memory consumption for flip buffers.
  * The actual memory limit is > 2x this amount.
  */
-#define TTYB_MEM_LIMIT 65536
+#define TTYB_DEFAULT_MEM_LIMIT 65536
 
 /*
  * We default to dicing tty buffer allocations to this many characters
@@ -89,7 +89,7 @@ void tty_buffer_unlock_exclusive(struct tty_port *port)
 
 int tty_buffer_space_avail(struct tty_port *port)
 {
-       int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);
+       int space = port->buf.mem_limit - atomic_read(&port->buf.memory_used);
        return max(space, 0);
 }
 
@@ -162,7 +162,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
 
        /* Should possibly check if this fails for the largest buffer we
           have queued and recycle that ? */
-       if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)
+       if (atomic_read(&port->buf.memory_used) > port->buf.mem_limit)
                return NULL;
        p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
        if (p == NULL)
@@ -536,4 +536,22 @@ void tty_buffer_init(struct tty_port *port)
        atomic_set(&buf->memory_used, 0);
        atomic_set(&buf->priority, 0);
        INIT_WORK(&buf->work, flush_to_ldisc);
+       buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT;
 }
+
+/**
+ *     tty_buffer_set_limit    -       change the tty buffer memory limit
+ *     @port: tty port to change
+ *
+ *     Change the tty buffer memory limit.
+ *     Must be called before the other tty buffer functions are used.
+ */
+
+int tty_buffer_set_limit(struct tty_port *port, int limit)
+{
+       if (limit < MIN_TTYB_SIZE)
+               return -EINVAL;
+       port->buf.mem_limit = limit;
+       return 0;
+}
+EXPORT_SYMBOL_GPL(tty_buffer_set_limit);

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 97d660ed70c1901407dac9ea49bd1036840e649c..2225745060d602f694c36777d350a0ccfe072dad 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -61,6 +61,7 @@ struct tty_bufhead {
        struct tty_buffer sentinel;
        struct llist_head free;         /* Free queue head */
        atomic_t           memory_used; /* In-use buffers excluding free list */
+       int                mem_limit;
        struct tty_buffer *tail;        /* Active buffer */
 };
 /*

diff --git a/include/linux/tty_flip.h b/include/linux/tty_flip.h
index 21ddd7d9ea1fe0303e5910b7de3019b9851e8bda..2da8bc2a5486017be70d7a11b83d0381a4fc0cc0 100644 (file)
--- a/include/linux/tty_flip.h
+++ b/include/linux/tty_flip.h
@@ -1,6 +1,7 @@
 #ifndef _LINUX_TTY_FLIP_H
 #define _LINUX_TTY_FLIP_H
 
+extern int tty_buffer_set_limit(struct tty_port *port, int limit);
 extern int tty_buffer_space_avail(struct tty_port *port);
 extern int tty_buffer_request_room(struct tty_port *port, size_t size);
 extern int tty_insert_flip_string_flags(struct tty_port *port,