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    Subject[PATCH v2 3/7] tty: Add fasync() hung up file operation
    Date
    VFS uses a two-stage check-and-call method for invoking file_operations
    methods, without explicitly snapshotting either the file_operations ptr
    or the function ptr. Since the tty core is one of the few VFS users that
    changes the f_op file_operations ptr of the file descriptor (when the
    tty has been hung up), and since the likelihood of the compiler generating
    a reload of either f_op or the function ptr is basically nil, just define
    a hung up fasync() file operation that returns an error.

    Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
    ---
    drivers/tty/tty_io.c | 6 ++++++
    1 file changed, 6 insertions(+)

    diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
    index e8b431e..05b0a9c 100644
    --- a/drivers/tty/tty_io.c
    +++ b/drivers/tty/tty_io.c
    @@ -468,6 +468,11 @@ static long hung_up_tty_compat_ioctl(struct file *file,
    return cmd == TIOCSPGRP ? -ENOTTY : -EIO;
    }

    +static int hung_up_tty_fasync(int fd, struct file *file, int on)
    +{
    + return -ENOTTY;
    +}
    +
    static const struct file_operations tty_fops = {
    .llseek = no_llseek,
    .read = tty_read,
    @@ -500,6 +505,7 @@ static const struct file_operations hung_up_tty_fops = {
    .unlocked_ioctl = hung_up_tty_ioctl,
    .compat_ioctl = hung_up_tty_compat_ioctl,
    .release = tty_release,
    + .fasync = hung_up_tty_fasync,
    };

    static DEFINE_SPINLOCK(redirect_lock);
    --
    2.7.0
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