readlink(2) handling of empty strings

readlink(2) handling of empty strings

[Ben Hutchings]

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readlink(2) claims:

       Since  Linux 2.6.39, pathname can be an empty string, in which case the
       call operates on the file referred to by dirfd  (which  may  have  been
       obtained using the open(2) O_PATH flag).  In this case, dirfd can refer
       to any type of file, not just a directory.

The last sentence seems to be incorrect.  dirfd must refer to a symlink
that has been opened using the O_PATH flag.  (The symlink could refer to
a file, directory, or nothing, but opening with O_PATH doesn't resolve
it.)

Ben.

-- 
Ben Hutchings
The two most common things in the universe are hydrogen and stupidity.

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Re: readlink(2) handling of empty strings

[Michael Kerrisk (man-pages)]

Hello Ben,

On 09/30/2014 01:33 AM, Ben Hutchings wrote:
> readlink(2) claims:
> 
>        Since  Linux 2.6.39, pathname can be an empty string, in which case the
>        call operates on the file referred to by dirfd  (which  may  have  been
>        obtained using the open(2) O_PATH flag).  In this case, dirfd can refer
>        to any type of file, not just a directory.
> 
> The last sentence seems to be incorrect.  dirfd must refer to a symlink
> that has been opened using the O_PATH flag.  (The symlink could refer to
> a file, directory, or nothing, but opening with O_PATH doesn't resolve
> it.)

Yes, you must be right. The existing text makes no sense; I suspect
a cut-and-paste error as I went through updating some of the *at.2 pages.
I've changed the text to:

       Since  Linux  2.6.39,  pathname  can be an empty string, in which
       case the call operates on the symbolic link referred to by  dirfd
       (which  should have have been obtained using the open(2) with the
       O_PATH and O_NOFOLLOW flags).

Okay?

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: readlink(2) handling of empty strings

[Ben Hutchings]

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On Tue, 2014-09-30 at 10:10 +0200, Michael Kerrisk (man-pages) wrote:
> Hello Ben,
> 
> On 09/30/2014 01:33 AM, Ben Hutchings wrote:
> > readlink(2) claims:
> > 
> >        Since  Linux 2.6.39, pathname can be an empty string, in which case the
> >        call operates on the file referred to by dirfd  (which  may  have  been
> >        obtained using the open(2) O_PATH flag).  In this case, dirfd can refer
> >        to any type of file, not just a directory.
> > 
> > The last sentence seems to be incorrect.  dirfd must refer to a symlink
> > that has been opened using the O_PATH flag.  (The symlink could refer to
> > a file, directory, or nothing, but opening with O_PATH doesn't resolve
> > it.)
> 
> Yes, you must be right. The existing text makes no sense; I suspect
> a cut-and-paste error as I went through updating some of the *at.2 pages.
> I've changed the text to:
> 
>        Since  Linux  2.6.39,  pathname  can be an empty string, in which
>        case the call operates on the symbolic link referred to by  dirfd
>        (which  should have have been obtained using the open(2) with the
>        O_PATH and O_NOFOLLOW flags).
> 
> Okay?

LGTM.

Ben.

-- 
Ben Hutchings
The two most common things in the universe are hydrogen and stupidity.

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