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    Subject[PATCH tty-next 2/5] tty: Enable configurable tty flip buffer limit
    Date
    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>
    ---
    drivers/tty/tty_buffer.c | 24 +++++++++++++++++++++---
    include/linux/tty.h | 1 +
    include/linux/tty_flip.h | 1 +
    3 files changed, 23 insertions(+), 3 deletions(-)

    diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
    index c043136f..57eb34b 100644
    --- 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 2f47989..58a34e7 100644
    --- 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 21ddd7d..2da8bc2 100644
    --- 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,
    --
    1.8.1.2


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