linux-kernel - Re: [patch] Fix type errors in inotify interfaces

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Date:	Wed, 19 Nov 2008 11:24:51 -0800
From:	"John McCutchan" <john@...nmccutchan.com>
To:	mtk.manpages@...il.com
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Robert Love" <rlove@...gle.com>,
	"Vegard Nossum" <vegard.nossum@...il.com>,
	"Ulrich Drepper" <drepper@...hat.com>
Subject: Re: [patch] Fix type errors in inotify interfaces

On Wed, Nov 19, 2008 at 11:10 AM, Michael Kerrisk
<mtk.manpages@...glemail.com> wrote:
> (Would be nice to see an Aacked-by from Robert or John on this patch.)
>
> On Wed, Nov 19, 2008 at 3:03 AM, Andrew Morton
> <akpm@...ux-foundation.org> wrote:
>> On Tue, 18 Nov 2008 15:18:21 -0500 Michael Kerrisk <mtk.manpages@...glemail.com> wrote:
>>
>>> Andrew,
>>>
>>> Vegard reminded me of an issue with the inotify interface
>>> that I raised quite a while ago, offlist, with Robert; Robert
>>> acknowledged that things should be fixed, but then neither of
>>> us actually did anything :-{.
>>>
>>> The problems lie in the types used for some inotify interfaces, both
>>> at the kernel level and at the glibc level.  This mail addresses the
>>> kernel problem.  I will follow up with some suggestions for glibc
>>> changes.
>>>
>>> For the sys_inotify_rm_watch() interface, the type of the 'wd' argument
>>> is currently 'u32', it should be '__s32' .  That is Robert's suggestion,
>>> and is consistent with the other declarations of watch descriptors in
>>> the kernel source, in particular, the inotify_event structure in
>>> include/linux/inotify.h:
>>>
>>> struct inotify_event {
>>>         __s32           wd;             /* watch descriptor */
>>>         __u32           mask;           /* watch mask */
>>>         __u32           cookie;         /* cookie to synchronize two events */
>>>         __u32           len;            /* length (including nulls) of name */
>>>         char            name[0];        /* stub for possible name */
>>> };
>>>
>>> The patch below makes the changes needed for inotify_rm_watch().
>>>
>>> Thanks
>>>
>>> Michael
>>>
>>>
>>> diff --git a/fs/inotify_user.c b/fs/inotify_user.c
>>> index d367e9b..a71f764 100644
>>> --- a/fs/inotify_user.c
>>> +++ b/fs/inotify_user.c
>>> @@ -704,7 +704,7 @@ fput_and_out:
>>>       return ret;
>>>  }
>>>
>>> -asmlinkage long sys_inotify_rm_watch(int fd, u32 wd)
>>> +asmlinkage long sys_inotify_rm_watch(int fd, __s32 wd)
>>>  {
>>>       struct file *filp;
>>>       struct inotify_device *dev;
>>> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
>>> index d6ff145..36983a5 100644
>>> --- a/include/linux/syscalls.h
>>> +++ b/include/linux/syscalls.h
>>> @@ -550,7 +550,7 @@ asmlinkage long sys_inotify_init(void);
>>>  asmlinkage long sys_inotify_init1(int flags);
>>>  asmlinkage long sys_inotify_add_watch(int fd, const char __user *path,
>>>                                       u32 mask);
>>> -asmlinkage long sys_inotify_rm_watch(int fd, u32 wd);
>>> +asmlinkage long sys_inotify_rm_watch(int fd, __s32 wd);
>>>
>>>  asmlinkage long sys_spu_run(int fd, __u32 __user *unpc,
>>>                                __u32 __user *ustatus);
>>
>
> Yes -- there is no sane reason for a negative watch descriptor to
> inotify_rm_watch(); this change is mainly about consistency.  (The
> glibc change is probably more important.)
>
>> otoh, the system call via which one _obtains_ watch descriptors most
>> certainly wants to return -ve nunmbers, to signify errors.
>>
>> All too hard.  I think I'll stop thinking about it and merge the patch ;)
>

Seems sane enough.

Acked-by: John McCutchan <john@...nmccutchan.com>

-- 
John McCutchan <john@...nmccutchan.com>
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