[Toybox] [PATCH] tail: implement -F (and its companion -s).

[enh]

On Thu, Jul 1, 2021 at 9:29 AM Rob Landley <rob at landley.net> wrote:

> On 6/30/21 6:57 PM, enh via Toybox wrote:
> > (Based on someone else's patch.)
> >
> > Implementing -F with inotify is a lot more work (including more
> > portability shims for macOS), so this is a simpler polling
> > implementation.
> >
> > Also fix my earlier mistake where xnotify_add() wasn't actually an 'x'
> > function that exits on failure.
>
> Applied, but:
>
> struct follow_file {
>   char *path;
>   int fd;
>   dev_t dev;
>   ino_t ino;
> };
>
> GLOBALS(
>   long n, c, s;
>   int file_no, last_fd;
>   struct xnotify *not;
>   struct follow_file *F;
> )
>
> Means that generated/globals.h has a pointer to an incomplete type, which
> the
> compiler allows (the union member is a pointer and it knows the size of
> that
> regardless what it points to) but makes me uncomfortable.
>
> What you're doing works, but possibly not for the _reason_ you think it
> does?
> Specifically, this patch has a structure defined before the GLOBALS()
> block and
> another defined after, and they might as well both be defined after
> because the
> one defined before GLOBALS() doesn't wind up in the header everything else
> includes, nor is it used to calculate the size of the union. So splitting
> them
> serves no purpose but _looks_ like it does.
>
> In toysh I'm doing the equivalent of:
>
> GLOBALS(
>   long n, c, s;
>   int file_no, last_fd;
>   struct xnotify *not;
>   struct tail_follow_file {
>     char *path;
>     int fd;
>     dev_t dev;
>     ino_t ino;
>   } *F;
> )
>
> Which is also a little awkward (nested structure definitions wind up in a
> global
> namespace, type prefixed with command name to avoid collisions in said
> global
> namespace...), but doing that allows me to embed instances of instructures
> and
> not just pointers to them. Elsewhere I've had the global one be a void *
> and
> typecast it on use, which is differntly awkward. This third way isn't
> necessarily MORE awkward, but I dislike having 3 ways to do the same thing
> in
> play in the same codebase.
>
> This is mostly a "code style" thing, I need to work out the preferred
> style for
> dealing with the context switch, and document the issue. (The compiler is
> forgiving, but I don't want to confuse people reading the code...)
>

yeah, i did scratch my head about that one for a bit before deciding to
punt the problem to you :-)

pointer to an incomplete type seemed better than void* but, yeah, moving
the struct definition below GLOBALS would have been more in keeping with
the rest of the tree.


> Rob
>
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