Re: [RFC] readlink()-related oddities

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From	Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: [RFC] readlink()-related oddities
Date	Fri, 20 Nov 2015 03:20:01 +0100
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On Thu, Nov 19, 2015 at 3:26 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> 1) atime updates, according to POSIX, should happen in case of success.
> For example, giving readlink(2) an unmapped buffer should _not_ touch
> atime.  Neither should calling readlink(2) in case if ->readlink() method
> returns e.g. -EIO or -ENOMEM.  We do atime update in those cases.  Looks
> like a bug and unless there's a good reason to keep that behaviour, I'd
> rather have it do what POSIX says.

I really don't think anybody cares, but I also don't think anybody
cares about the current behavior, so we can certainly fix it to match
POSIX wording, and just move it a bit lower after checking the return
value from ->realink().

> 3) normally, readlink(2) fails for non-symlinks.  Moreover, according to
> POSIX it should do so (with -EINVAL).

I don't think POSIX is necessarily relevant here.

We have had magic file behavior outside the scope of POSIX before, and
we will have it in the future. It makes perfect sense to use
readlink() for management tools for automounting, even if the normal
oepration is to treat the thing as a directory.

Not everything is within the domain of POSIX.

               Linus
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Thread

[RFC] readlink()-related oddities Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-20 00:30 +0100
  Re: [RFC] readlink()-related oddities Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-20 03:20 +0100
    Re: [RFC] readlink()-related oddities Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-20 04:00 +0100
      Re: [RFC] readlink()-related oddities Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-20 04:10 +0100
        Re: [RFC] readlink()-related oddities Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-20 04:20 +0100
          Re: [RFC] readlink()-related oddities Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-20 04:30 +0100
      Re: [RFC] readlink()-related oddities David Howells <dhowells@redhat.com> - 2015-11-20 11:10 +0100
  Re: [RFC] readlink()-related oddities David Howells <dhowells@redhat.com> - 2015-11-20 11:00 +0100
    Re: [RFC] readlink()-related oddities Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-20 17:10 +0100
      Re: [RFC] readlink()-related oddities David Howells <dhowells@redhat.com> - 2015-11-20 17:30 +0100
    Re: [RFC] readlink()-related oddities Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-20 23:40 +0100

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