linux-kernel - Description of open_to_namei

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Date:	Thu, 12 Feb 2009 12:10:58 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:	linux-fsdevel@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org
Subject: Description of open_to_namei_flags()?

Hello.

> /*
>  * Note that while the flag value (low two bits) for sys_open means:
>  *      00 - read-only
>  *      01 - write-only
>  *      10 - read-write
>  *      11 - special
>  * it is changed into
>  *      00 - no permissions needed
>  *      01 - read-permission
>  *      10 - write-permission
>  *      11 - read-write
>  * for the internal routines (ie open_namei()/follow_link() etc)
>  * This is more logical, and also allows the 00 "no perm needed"
>  * to be used for symlinks (where the permissions are checked
>  * later).
>  *
>  */
> static inline int open_to_namei_flags(int flag)
> {
> 	if ((flag+1) & O_ACCMODE)
> 		flag++;
> 	return flag;
> }

I noticed that open_to_namei_flags() can't yield
"00 - no permissions needed" output for "11 - special" input.
To yield "00 - no permissions needed" output for "11 - special" input,
I think

  static inline int open_to_namei_flags(int flag)
  {
  	return (flag + 1) & O_ACCMODE;
  }

is needed.

sys_open(path, 0) is open for reading.
sys_open(path, 1) is open for writing.
sys_open(path, 2) is open for reading and writing.
What is sys_open(path, 3) for?

Regards.
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