Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs directory

From	Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs directory
Date	2015-11-10 06:00 +0100
Message-ID	<qt9cd-nP-7@gated-at.bofh.it> (permalink)
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On Mon, Nov 09, 2015 at 05:01:18PM -0600, Chris J Arges wrote:
> On 11/09/2015 02:56 PM, Josh Poimboeuf wrote:
> > I'd recommend splitting this up into two separate patches:
> > 
> > 1. introduce old_sympos
> > 2. change the sysfs interface
> > 
> > On Mon, Nov 09, 2015 at 10:16:05AM -0600, Chris J Arges wrote:
> >> In cases of duplicate symbols in vmlinux, old_sympos will be used to
> >> disambiguate instead of old_addr. Normally old_sympos will be 0, and
> >> default to only returning the first found instance of that symbol. If an
> >> incorrect symbol position is specified then livepatching will fail.
> > 
> > In the case of old_sympos == 0, instead of just returning the first
> > symbol it finds, I think it should ensure that the symbol is unique.  As
> > Miroslav suggested:
> > 
> >   0 - default, preserve more or less current behaviour. If the symbol is 
> >       unique there is no problem. If it is not the patching would fail.
> >   1, 2, ... - occurrence of the symbol in kallsyms.
> >   
> >   The advantage is that if the user does not care and is certain that the 
> >   symbol is unique he doesn't have to do anything. If the symbol is not 
> >   unique he still has means how to solve it.
> > 
> 
> So one part that will be confusing here is as follows.
> 
> If '0' is specified for old_sympos, should the symbol be 'func_name,0'
> or 'func_name,1' provided we have a unique symbol? We could also default
> to 'what the user provides', but this seems odd.

I don't feel strongly either way, but I think using the same number the
user provides is fine, since it makes the sysfs interface consistent
with the old_sympos usage.

> Another option would be to use no postfix when 0 is given, and only
> introduce the ',n' postfix if old_sympos is > 0.

IMO always having a suffix is good, as it makes parsing less surprising
and less error-prone.

> >>  static int klp_write_object_relocations(struct module *pmod,
> >> @@ -307,7 +318,7 @@ static int klp_write_object_relocations(struct module *pmod,
> >>  			else
> >>  				ret = klp_find_object_symbol(obj->mod->name,
> >>  							     reloc->name,
> >> -							     &reloc->val);
> >> +							     &reloc->val, 0);
> > 
> > I think it would be a good idea to also add old_sympos to klp_reloc so
> > the relocation code is consistent with the klp_func symbol addressing.
> >
> 
> So you are thinking as an optional external field as well? I'll have to
> look at this a bit more but makes sense to me.

Yeah, the semantics would be the same as klp_func.old_sympos.  We could
add a new klp_reloc.sympos and make klp_reloc.val a private field.

-- 
Josh
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Thread

[PATCH] livepatch: old_name.number scheme in livepatch sysfs directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-02 19:00 +0100
  Re: livepatch: old_name.number scheme in livepatch sysfs directory Jessica Yu <jeyu@redhat.com> - 2015-11-02 20:20 +0100
  Re: [PATCH] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-02 21:00 +0100
    Re: [PATCH] livepatch: old_name.number scheme in livepatch sysfs  directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-02 21:20 +0100
      Re: [PATCH] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-02 21:40 +0100
        [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-03 00:10 +0100
          Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-03 11:00 +0100
            Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-03 16:10 +0100
          Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-03 12:00 +0100
            Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Petr Mladek <pmladek@suse.com> - 2015-11-03 13:50 +0100
              Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-03 16:10 +0100
              Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Jiri Kosina <jikos@kernel.org> - 2015-11-03 21:00 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-03 21:10 +0100
                [PATCH 1/3 v4] livepatch: add old_sympos as disambiguator field to klp_func Chris J Arges <chris.j.arges@canonical.com> - 2015-11-11 17:30 +0100
                Re: [PATCH 1/3 v4] livepatch: add old_sympos as disambiguator field  to klp_func Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-11 18:50 +0100
                Re: [PATCH 1/3 v4] livepatch: add old_sympos as disambiguator field  to klp_func Miroslav Benes <mbenes@suse.cz> - 2015-11-12 11:30 +0100
                [PATCH 3/3 v4] livepatch: old_name,number scheme in livepatch sysfs directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-11 17:40 +0100
                Re: [PATCH 3/3 v4] livepatch: old_name,number scheme in livepatch  sysfs directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-11 19:10 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Chris J Arges <chris.j.arges@canonical.com> - 2015-11-11 17:40 +0100
                [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field to klp_reloc Chris J Arges <chris.j.arges@canonical.com> - 2015-11-11 17:40 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-11 19:00 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Petr Mladek <pmladek@suse.com> - 2015-11-12 15:40 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-12 20:20 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Petr Mladek <pmladek@suse.com> - 2015-11-13 15:00 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-13 18:00 +0100
                Re: [PATCH 2/3 v4] livepatch: add old_sympos as disambiguator field  to klp_reloc Miroslav Benes <mbenes@suse.cz> - 2015-11-12 11:30 +0100
            Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-03 16:00 +0100
              Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-03 17:20 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-03 18:00 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-03 21:50 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-04 11:00 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-04 17:10 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-04 17:20 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-05 16:20 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-05 17:00 +0100
                Re: [PATCH v2] livepatch: old_name.number scheme in livepatch sysfs  directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-05 17:10 +0100
                [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-09 17:20 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-09 22:00 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Chris J Arges <chris.j.arges@canonical.com> - 2015-11-10 00:10 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-10 06:00 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-10 09:50 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Josh Poimboeuf <jpoimboe@redhat.com> - 2015-11-10 14:50 +0100
                Re: [PATCH v3] livepatch: old_name,number scheme in livepatch sysfs  directory Miroslav Benes <mbenes@suse.cz> - 2015-11-10 10:10 +0100

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