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    SubjectRe: Real-Time Preemption and UML?
    Well, I keep trying a little bit more. In the mean while you can get some
    of the stuff I needed to change to at least get it to compile:

    One of the problems was use of direct architecture specific semaphores
    (which doesn't work under PREEMPT_REALTIME) and in places where a quick
    (maybe too quick) look at the code told me that completions ought to be
    used. Therefore I changed two semaphores to completions which compiled
    fine. I have tried the change on 2.6.11-rc2, and it seemed to work, but I
    have not tested it heavily.

    The patch is in an attachment - I hope the mail-list will alow that. It is
    simply too trouplesome otherwise when I am using Pine as mail client.

    Esben


    On Mon, 7 Feb 2005, Jeff Dike wrote:

    > simlo@phys.au.dk said:
    > > Hi, I am trying to compile and run UM-Linux with PREEMPT_REALTIME. I
    > > managed to get it to compile but it wont start - it simply stops
    > > somewhere in start_kernel() :-(
    >
    > I've never played with preemption on UML. No doubt it needs some work...
    >
    > Jeff
    >
    > -
    > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > Please read the FAQ at http://www.tux.org/lkml/
    >
    --- linux-2.6.11-rc2-um/arch/um/drivers/port_kern.c.orig 2005-01-23 15:53:29.000000000 +0100
    +++ linux-2.6.11-rc2-um/arch/um/drivers/port_kern.c 2005-02-06 19:54:52.000000000 +0100
    @@ -23,7 +23,7 @@
    struct port_list {
    struct list_head list;
    int has_connection;
    - struct semaphore sem;
    + struct completion done;
    int port;
    int fd;
    spinlock_t lock;
    @@ -66,7 +66,7 @@
    conn->fd = fd;
    list_add(&conn->list, &conn->port->connections);

    - up(&conn->port->sem);
    + complete(&conn->port->done);
    return(IRQ_HANDLED);
    }

    @@ -183,13 +183,14 @@
    *port = ((struct port_list)
    { .list = LIST_HEAD_INIT(port->list),
    .has_connection = 0,
    - .sem = __SEMAPHORE_INITIALIZER(port->sem,
    - 0),
    .lock = SPIN_LOCK_UNLOCKED,
    .port = port_num,
    .fd = fd,
    .pending = LIST_HEAD_INIT(port->pending),
    .connections = LIST_HEAD_INIT(port->connections) });
    +
    + init_completion(&port->done),
    +
    list_add(&port->list, &ports);

    found:
    @@ -221,7 +222,7 @@
    int fd;

    while(1){
    - if(down_interruptible(&port->sem))
    + if(wait_for_completion_interruptible(&port->done))
    return(-ERESTARTSYS);

    spin_lock(&port->lock);
    --- linux-2.6.11-rc2-um/arch/um/drivers/xterm_kern.c.orig 2005-01-23 15:53:29.000000000 +0100
    +++ linux-2.6.11-rc2-um/arch/um/drivers/xterm_kern.c 2005-02-06 19:54:58.000000000 +0100
    @@ -16,7 +16,7 @@
    #include "xterm.h"

    struct xterm_wait {
    - struct semaphore sem;
    + struct completion ready;
    int fd;
    int pid;
    int new_fd;
    @@ -32,7 +32,7 @@
    return(IRQ_NONE);

    xterm->new_fd = fd;
    - up(&xterm->sem);
    + complete(&xterm->ready);
    return(IRQ_HANDLED);
    }

    @@ -49,10 +49,10 @@

    /* This is a locked semaphore... */
    *data = ((struct xterm_wait)
    - { .sem = __SEMAPHORE_INITIALIZER(data->sem, 0),
    - .fd = socket,
    + { .fd = socket,
    .pid = -1,
    .new_fd = -1 });
    + init_completion(&data->ready);

    err = um_request_irq(XTERM_IRQ, socket, IRQ_READ, xterm_interrupt,
    SA_INTERRUPT | SA_SHIRQ | SA_SAMPLE_RANDOM,
    @@ -68,7 +68,7 @@
    *
    * XXX Note, if the xterm doesn't work for some reason (eg. DISPLAY
    * isn't set) this will hang... */
    - down(&data->sem);
    + wait_for_completion(&data->ready);

    free_irq_by_irq_and_dev(XTERM_IRQ, data);
    free_irq(XTERM_IRQ, data);
    \
     
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