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    Subject[PATCH 04/79] tty-ldisc: make /proc/tty/ldiscs use ldisc_ops instead of ldiscs
    Date
    From: Linus Torvalds <torvalds@linux-foundation.org>

    The /proc/tty/ldiscs file is totally and utterly un-interested in the
    "struct tty_ldisc" structures, and only cares about the underlying ldisc
    operations.

    So don't make it create a dummy 'struct ldisc' only to get a pointer to
    the operations, and then destroy it. Instead, we split up the function
    'tty_ldisc_try_get()', and create a 'get_ldops()' helper that just looks
    up the ldisc operations based on the ldisc number.

    That makes the code simpler to read (smaller and more well-defined
    helper functions), and allows the /proc functions to avoid creating that
    useless dummy only to immediately free it again.

    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Tested-by: Sergey Senozhatsky <sergey.senozhatsky@mail.by>
    Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
    Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    drivers/char/tty_ldisc.c | 65 +++++++++++++++++++++++++++------------------
    1 files changed, 39 insertions(+), 26 deletions(-)

    diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
    index e48af9f..cbfacc0 100644
    --- a/drivers/char/tty_ldisc.c
    +++ b/drivers/char/tty_ldisc.c
    @@ -145,6 +145,34 @@ int tty_unregister_ldisc(int disc)
    }
    EXPORT_SYMBOL(tty_unregister_ldisc);

    +static struct tty_ldisc_ops *get_ldops(int disc)
    +{
    + unsigned long flags;
    + struct tty_ldisc_ops *ldops, *ret;
    +
    + spin_lock_irqsave(&tty_ldisc_lock, flags);
    + ret = ERR_PTR(-EINVAL);
    + ldops = tty_ldiscs[disc];
    + if (ldops) {
    + ret = ERR_PTR(-EAGAIN);
    + if (try_module_get(ldops->owner)) {
    + ldops->refcount++;
    + ret = ldops;
    + }
    + }
    + spin_unlock_irqrestore(&tty_ldisc_lock, flags);
    + return ret;
    +}
    +
    +static void put_ldops(struct tty_ldisc_ops *ldops)
    +{
    + unsigned long flags;
    +
    + spin_lock_irqsave(&tty_ldisc_lock, flags);
    + ldops->refcount--;
    + module_put(ldops->owner);
    + spin_unlock_irqrestore(&tty_ldisc_lock, flags);
    +}

    /**
    * tty_ldisc_try_get - try and reference an ldisc
    @@ -156,36 +184,21 @@ EXPORT_SYMBOL(tty_unregister_ldisc);

    static struct tty_ldisc *tty_ldisc_try_get(int disc)
    {
    - unsigned long flags;
    struct tty_ldisc *ld;
    struct tty_ldisc_ops *ldops;
    - int err = -EINVAL;

    ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL);
    if (ld == NULL)
    return ERR_PTR(-ENOMEM);

    - spin_lock_irqsave(&tty_ldisc_lock, flags);
    - ld->ops = NULL;
    - ldops = tty_ldiscs[disc];
    - /* Check the entry is defined */
    - if (ldops) {
    - /* If the module is being unloaded we can't use it */
    - if (!try_module_get(ldops->owner))
    - err = -EAGAIN;
    - else {
    - /* lock it */
    - ldops->refcount++;
    - ld->ops = ldops;
    - atomic_set(&ld->users, 1);
    - err = 0;
    - }
    - }
    - spin_unlock_irqrestore(&tty_ldisc_lock, flags);
    - if (err) {
    + ldops = get_ldops(disc);
    + if (IS_ERR(ldops)) {
    kfree(ld);
    - return ERR_PTR(err);
    + return ERR_CAST(ldops);
    }
    +
    + ld->ops = ldops;
    + atomic_set(&ld->users, 1);
    return ld;
    }

    @@ -234,13 +247,13 @@ static void tty_ldiscs_seq_stop(struct seq_file *m, void *v)
    static int tty_ldiscs_seq_show(struct seq_file *m, void *v)
    {
    int i = *(loff_t *)v;
    - struct tty_ldisc *ld;
    + struct tty_ldisc_ops *ldops;

    - ld = tty_ldisc_try_get(i);
    - if (IS_ERR(ld))
    + ldops = get_ldops(i);
    + if (IS_ERR(ldops))
    return 0;
    - seq_printf(m, "%-10s %2d\n", ld->ops->name ? ld->ops->name : "???", i);
    - put_ldisc(ld);
    + seq_printf(m, "%-10s %2d\n", ldops->name ? ldops->name : "???", i);
    + put_ldops(ldops);
    return 0;
    }

    --
    1.6.4.2


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