Description of open_to_namei_flags()?

Description of open_to_namei_flags()?

[Tetsuo Handa]

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.

Re: Description of open_to_namei_flags()?

[Al Viro]

On Thu, Feb 12, 2009 at 12:10:58PM +0900, Tetsuo Handa wrote:
> > 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.

No.  Comments are rather misleading; the code is correct.

> 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?

open for ioctls only; checks for rw permissions, doesn't allow read or
write calls.  Note that the latter is controlled by ->f_mode, which does
*not* come from open_to_namei_flags() (and is calculated as you suggested).
Results of open_to_namei_flags() are used for permission checks, where
3 -> read|write is correct.