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

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Date:	Wed, 19 Nov 2008 00:03:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michael Kerrisk <mtk.manpages@...glemail.com>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Robert Love <rlove@...gle.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [patch] Fix type errors in inotify interfaces

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);

hrm.  I see no sane reason why a watch descriptor should take on
negative values, so in some ways the u32 was logical.  (Ditto file
descriptors, but I don't think I want to change that ;))

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 ;)
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