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Re: [PATCH] diff: add support for reading files literally with --no-index




On Thu, Jan 03, 2019 at 06:18:55PM -0800, Jonathan Nieder wrote:
> I may be a minority in this opinion, but I had trouble understanding
> what --literally would do from its name.  I suspect we can come up
> with a better name.
> 
> Unfortunately, I'm terrible at coming up with names. :-P
> 
> --dereference would be a good name when it comes to symlinks, but
> it's not a good name for reading what is on the other side of a pipe.
> On the plus side, it matches "diff" and "cp"'s name for the "follow
> symbolic links" option.
> 
> --plain captures the desire a little better --- we want a plain
> read(2) from the file instead of trying to be smart and look at
> whether it is e.g. a block device.  But in the context of "diff", that
> would seem more like an option that affects the output.
> 
> What would you think of
> 
>  - always reading from fifos instead of describing them, since I've
>    never encountered a use case where people want the latter
> 
>  - --dereference to control whether to follow symlinks

This is actually surprisingly difficult. The reason I implemented this
only for no-index mode is because there are actually several places we
can stat a file in the diff code, and implementing a --dereference
option that catches all of those cases and getting the option passed
down to them is non-trivial.

Since my primary environment is on Linux, I need to implement functional
--dereference semantics before implementing the FIFO functionality to
know if it works in my use case.

I agree that would be a nicer approach overall, so let me see if I can
take another stab at it in a way that isn't excessively complex. It
would also make the name less controversial, since "--dereference" is
the obvious choice for dereferencing symlinks.

> [...]
> > --- a/diff-no-index.c
> > +++ b/diff-no-index.c
> > @@ -75,7 +75,25 @@ static int populate_from_stdin(struct diff_filespec *s)
> >  	return 0;
> >  }
> >  
> > -static struct diff_filespec *noindex_filespec(const char *name, int mode)
> > +static int populate_literally(struct diff_filespec *s)
> > +{
> > +	struct strbuf buf = STRBUF_INIT;
> > +	size_t size = 0;
> > +	int fd = xopen(s->path, O_RDONLY);
> > +
> > +	if (strbuf_read(&buf, fd, 0) < 0)
> > +		return error_errno("error while reading from '%s'", s->path);
> > +
> > +	s->should_munmap = 0;
> > +	s->data = strbuf_detach(&buf, &size);
> > +	s->size = size;
> > +	s->should_free = 1;
> > +	s->read_literally = 1;
> 
> Oh!  --read-literally works perfectly for me as a name. :)

If I can't manage to split this out into two pieces, I'll pick that as
the name for the reroll.
-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204

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