It's a bit strange to see tty_register_ldisc() call in modules' exit functions.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
Documentation/tty.txt | 2 +-
drivers/char/tty_io.c | 35 ++++++++++++++++++++++++-----------
include/linux/tty.h | 1 +
3 files changed, 26 insertions(+), 12 deletions(-)
diff -uprN linux-tty_register_ldisc_000/Documentation/tty.txt linux-tty_register_ldisc_001/Documentation/tty.txt
--- linux-tty_register_ldisc_000/Documentation/tty.txt 2005-05-31 20:12:47.000000000 +0400
+++ linux-tty_register_ldisc_001/Documentation/tty.txt 2005-05-31 23:19:32.000000000 +0400
@@ -22,7 +22,7 @@ copy of the structure. You must not re-r
discipline even with the same data or your computer again will be eaten by
demons.
-In order to remove a line discipline call tty_register_ldisc passing NULL.
+In order to remove a line discipline call tty_unregister_ldisc().
In ancient times this always worked. In modern times the function will
return -EBUSY if the ldisc is currently in use. Since the ldisc referencing
code manages the module counts this should not usually be a concern.
diff -uprN linux-tty_register_ldisc_000/drivers/char/tty_io.c linux-tty_register_ldisc_001/drivers/char/tty_io.c
--- linux-tty_register_ldisc_000/drivers/char/tty_io.c 2005-05-31 20:13:34.000000000 +0400
+++ linux-tty_register_ldisc_001/drivers/char/tty_io.c 2005-05-31 23:17:40.000000000 +0400
@@ -262,17 +262,10 @@ int tty_register_ldisc(int disc, struct
return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags);
- if (new_ldisc) {
- tty_ldiscs[disc] = *new_ldisc;
- tty_ldiscs[disc].num = disc;
- tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
- tty_ldiscs[disc].refcount = 0;
- } else {
- if(tty_ldiscs[disc].refcount)
- ret = -EBUSY;
- else
- tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
- }
+ tty_ldiscs[disc] = *new_ldisc;
+ tty_ldiscs[disc].num = disc;
+ tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
+ tty_ldiscs[disc].refcount = 0;
spin_unlock_irqrestore(&tty_ldisc_lock, flags);
return ret;
@@ -280,6 +273,26 @@ int tty_register_ldisc(int disc, struct
EXPORT_SYMBOL(tty_register_ldisc);
+int tty_unregister_ldisc(int disc)
+{
+ unsigned long flags;
+ int ret = 0;
+
+ if (disc < N_TTY || disc >= NR_LDISCS)
+ return -EINVAL;
+
+ spin_lock_irqsave(&tty_ldisc_lock, flags);
+ if (tty_ldiscs[disc].refcount)
+ ret = -EBUSY;
+ else
+ tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
+ spin_unlock_irqrestore(&tty_ldisc_lock, flags);
+
+ return ret;
+}
+
+EXPORT_SYMBOL(tty_unregister_ldisc);
+
struct tty_ldisc *tty_ldisc_get(int disc)
{
unsigned long flags;
diff -uprN linux-tty_register_ldisc_000/include/linux/tty.h linux-tty_register_ldisc_001/include/linux/tty.h
--- linux-tty_register_ldisc_000/include/linux/tty.h 2005-05-31 20:15:51.000000000 +0400
+++ linux-tty_register_ldisc_001/include/linux/tty.h 2005-05-31 23:18:23.000000000 +0400
@@ -345,6 +345,7 @@ extern int tty_check_change(struct tty_s
extern void stop_tty(struct tty_struct * tty);
extern void start_tty(struct tty_struct * tty);
extern int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc);
+extern int tty_unregister_ldisc(int disc);
extern int tty_register_driver(struct tty_driver *driver);
extern int tty_unregister_driver(struct tty_driver *driver);
extern void tty_register_device(struct tty_driver *driver, unsigned index, struct device *dev);
This patch is wrong. Please do not apply.
An unmodified ldisc driver (externally maintained) will continue to call
tty_register_ldisc with NULL, but the new behavior will be to set the
ldisc pointer to NULL but have LDISC_FLAG_DEFINED set.
If you feel it is absolutely necessary to add this new function
for cosmetic reasons, then leave the old behavior in place
and make tty_unregister_ldisc a wrapper to tty_register_ldisc
that uses a NULL pointer.
This preserves sanity and compatibility.
The existing function has a bug:
If new_ldisc != NULL and LDISC_FLAG_DEFINED is set,
the ldisc is switched to new_ldisc without checking
for non-zero refcount of current ldisc.
--
Paul Fulghum
[email protected]
On Tue, 2005-05-31 at 23:56 +0400, Alexey Dobriyan wrote:
> It's a bit strange to see tty_register_ldisc() call in modules' exit functions.
> ...
> --- linux-tty_register_ldisc_000/Documentation/tty.txt 2005-05-31 20:12:47.000000000 +0400
> +++ linux-tty_register_ldisc_001/Documentation/tty.txt 2005-05-31 23:19:32.000000000 +0400
> @@ -22,7 +22,7 @@ copy of the structure. You must not re-r
> discipline even with the same data or your computer again will be eaten by
> demons.
>
> -In order to remove a line discipline call tty_register_ldisc passing NULL.
> +In order to remove a line discipline call tty_unregister_ldisc().
> In ancient times this always worked. In modern times the function will
> return -EBUSY if the ldisc is currently in use. Since the ldisc referencing
> code manages the module counts this should not usually be a concern.
> diff -uprN linux-tty_register_ldisc_000/drivers/char/tty_io.c linux-tty_register_ldisc_001/drivers/char/tty_io.c
> --- linux-tty_register_ldisc_000/drivers/char/tty_io.c 2005-05-31 20:13:34.000000000 +0400
> +++ linux-tty_register_ldisc_001/drivers/char/tty_io.c 2005-05-31 23:17:40.000000000 +0400
> @@ -262,17 +262,10 @@ int tty_register_ldisc(int disc, struct
> return -EINVAL;
>
> spin_lock_irqsave(&tty_ldisc_lock, flags);
> - if (new_ldisc) {
> - tty_ldiscs[disc] = *new_ldisc;
> - tty_ldiscs[disc].num = disc;
> - tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
> - tty_ldiscs[disc].refcount = 0;
> - } else {
> - if(tty_ldiscs[disc].refcount)
> - ret = -EBUSY;
> - else
> - tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
> - }
> + tty_ldiscs[disc] = *new_ldisc;
> + tty_ldiscs[disc].num = disc;
> + tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
> + tty_ldiscs[disc].refcount = 0;
> spin_unlock_irqrestore(&tty_ldisc_lock, flags);
>
> return ret;
> @@ -280,6 +273,26 @@ int tty_register_ldisc(int disc, struct
>
> EXPORT_SYMBOL(tty_register_ldisc);
>
> +int tty_unregister_ldisc(int disc)
> +{
> + unsigned long flags;
> + int ret = 0;
> +
> + if (disc < N_TTY || disc >= NR_LDISCS)
> + return -EINVAL;
> +
> + spin_lock_irqsave(&tty_ldisc_lock, flags);
> + if (tty_ldiscs[disc].refcount)
> + ret = -EBUSY;
> + else
> + tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
> + spin_unlock_irqrestore(&tty_ldisc_lock, flags);
> +
> + return ret;
> +}
> +
> +EXPORT_SYMBOL(tty_unregister_ldisc);
> +
> struct tty_ldisc *tty_ldisc_get(int disc)
> {
> unsigned long flags;
> diff -uprN linux-tty_register_ldisc_000/include/linux/tty.h linux-tty_register_ldisc_001/include/linux/tty.h
> --- linux-tty_register_ldisc_000/include/linux/tty.h 2005-05-31 20:15:51.000000000 +0400
> +++ linux-tty_register_ldisc_001/include/linux/tty.h 2005-05-31 23:18:23.000000000 +0400
> @@ -345,6 +345,7 @@ extern int tty_check_change(struct tty_s
> extern void stop_tty(struct tty_struct * tty);
> extern void start_tty(struct tty_struct * tty);
> extern int tty_register_ldisc(int disc, struct tty_ldisc *new_ldisc);
> +extern int tty_unregister_ldisc(int disc);
> extern int tty_register_driver(struct tty_driver *driver);
> extern int tty_unregister_driver(struct tty_driver *driver);
> extern void tty_register_device(struct tty_driver *driver, unsigned index, struct device *dev);
> -
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> Please read the FAQ at http://www.tux.org/lkml/
--
--
Paul Fulghum
[email protected]
On Tue, 2005-05-31 at 17:28 -0500, Paul Fulghum wrote:
> An unmodified ldisc driver (externally maintained) will continue to call
> tty_register_ldisc with NULL, but the new behavior will be to set the
> ldisc pointer to NULL but have LDISC_FLAG_DEFINED set.
I was partially wrong.
After Alexey's patch, a NULL new_ldisc is accessed
(not assigned) causing an oops. This is still not
good behavior.
As for the refcount bug, this patch should fix it.
Comments?
--
Paul Fulghum
[email protected]
--- linux-2.6.11/drivers/char/tty_io.c 2005-03-02 01:38:10.000000000 -0600
+++ b/drivers/char/tty_io.c 2005-05-31 22:10:41.000000000 -0500
@@ -262,16 +262,16 @@ int tty_register_ldisc(int disc, struct
return -EINVAL;
spin_lock_irqsave(&tty_ldisc_lock, flags);
- if (new_ldisc) {
+ if ((tty_ldiscs[disc].flags & LDISC_FLAG_DEFINED) &&
+ tty_ldiscs[disc].refcount)
+ ret = -EBUSY;
+ else if (new_ldisc) {
tty_ldiscs[disc] = *new_ldisc;
tty_ldiscs[disc].num = disc;
tty_ldiscs[disc].flags |= LDISC_FLAG_DEFINED;
tty_ldiscs[disc].refcount = 0;
} else {
- if(tty_ldiscs[disc].refcount)
- ret = -EBUSY;
- else
- tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
+ tty_ldiscs[disc].flags &= ~LDISC_FLAG_DEFINED;
}
spin_unlock_irqrestore(&tty_ldisc_lock, flags);