linux-kernel - Re: [PATCH] DocBook: Avoid stdout junk with no man pages to compress

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Date:	Tue, 14 Jul 2015 06:27:11 +0200
From:	Ulf Magnusson <ulfalizer.lkml@...il.com>
To:	Jim Davis <jim.epost@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-doc <linux-doc@...r.kernel.org>,
	Michal Marek <mmarek@...e.cz>,
	Jonathan Corbet <corbet@....net>,
	Herbert Xu <herbert@...dor.apana.org.au>, smueller@...onox.de,
	Ulf Magnusson <ulfalizer@...il.com>
Subject: Re: [PATCH] DocBook: Avoid stdout junk with no man pages to compress

On Mon, Jul 13, 2015 at 2:46 AM, Ulf Magnusson <ulfalizer.lkml@...il.com> wrote:
> On Sun, Jul 12, 2015 at 04:36:53PM -0700, Jim Davis wrote:
>> On Sun, Jul 12, 2015 at 2:59 PM, Ulf Magnusson <ulfalizer.lkml@...il.com> wrote:
>> > gzip would run as 'gzip -f' when no uncompressed man pages were found,
>> > making it compress the (empty) stdin to stdout.
>>
>> > --- a/Documentation/DocBook/Makefile
>> > +++ b/Documentation/DocBook/Makefile
>> > @@ -56,7 +56,7 @@ htmldocs: $(HTML)
>> >
>> >  MAN := $(patsubst %.xml, %.9, $(BOOKS))
>> >  mandocs: $(MAN)
>> > -       find $(obj)/man -name '*.9' | xargs gzip -f
>> > +       find $(obj)/man -name '*.9' -exec gzip -f {} \;
>> >
>> >  installmandocs: mandocs
>> >         mkdir -p /usr/local/man/man9/
>>
>> That does get rid of the binary burp, but 'xargs gzip -f'  has been in
>> the Makefile since January, and gzipping '\n' just started recently.
>> So what's changed?
>>
>
> No idea. I just assumed it had been broken since then, since the version
> before d56fcf299fb4 (DocBook: Do not exceed argument list limit) looked
> for *.9 files before running gzip:
>
> mandocs: $(MAN)
>         $(if $(wildcard $(obj)/man/*.9),gzip -f $(obj)/man/*.9)
>
>> It looks like, for whatever reason, make installmandocs always ends up
>> rerunning mandocs -- there's now a 'GEN  Documentation
>> Docbook//v4l2.xml' printed, and that extra mandocs invocation is where
>> the problematic second invocation of find is coming from.  I won't
>> pretend to understand the Makefile flow to guess at why that's
>> happening, but obviously 'make mandocs; make installmandocs' shouldn't
>> need to regenerate things already generated.
>
> I won't pretend to understand the Makefile flow either. Guess it might
> be worth looking into v4l2.xml as well then. Could be some directory
> shenanigans going on judging from the '//'.
>

I looked into it some more, and I'm now fairly certain that 'mandocs' always
runs its recipe regardless of the status of the prerequisites. Changing the
top-level Makefile to do

        $(Q)$(MAKE) --debug=v $(build)=Documentation/DocBook $@

and running 'make mandocs', you see some FORCEs in the output, which -- unless
my make fu is weak -- causes all the targets above that to always be considered
out of date:

File 'mandocs' does not exist.
 Considering target file 'Documentation/DocBook/z8530book.9'.
   Considering target file 'Documentation/DocBook/z8530book.xml'.
     ...
     Considering target file 'FORCE'.
      File 'FORCE' does not exist.
      Finished prerequisites of target file 'FORCE'.
     Must remake target 'FORCE'.
     Successfully remade target file 'FORCE'.
     ...
   Must remake target 'Documentation/DocBook/z8530book.xml'.
 ...
Must remake target 'mandocs'.


Re. the 'GEN  Documentation Docbook//v4l2.xml', I think the problem is the
following rule in Documentation/DocBook/media/Makefile:

$(MEDIA_OBJ_DIR)/v4l2.xml: $(OBJIMGFILES)
        @$($(quiet)gen_xml)
        @(ln -sf `cd $(MEDIA_SRC_DIR) && /bin/pwd`/v4l/*xml $(MEDIA_OBJ_DIR)/)
        @(ln -sf `cd $(MEDIA_SRC_DIR) && /bin/pwd`/dvb/*xml $(MEDIA_OBJ_DIR)/)

./Documentation/DocBook/v4l2.xml is a symlink, so make compares the
modification time of the symlink *target* (which is never updated) against the
image (*.png, *.gif, etc.) files in $(OBJIMGFILES). Updating the symlink itself
won't change that modification time, so that's why it always runs.

Passing --check-symlink-times to make so that it also looks at the modification
time of the symlink seems to change a bunch of other stuff in the output too.
Maybe there's other problems lurking here as well.

>>
>> In any event,
>>
>> Tested-by: Jim Davis <jim.epost@...il.com>
>>
>> Jim
>
> I just noticed the commit message only mentions the alternative
> solutions and not the implemented solution. Could send a v2 that fixes
> that, but I'll wait for more comments first.
>
> Cheers,
> Ulf

Cheers,
Ulf
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