Re: [PATCH] gdb/debuginfod: Prevent prompt for continue during downloading.

[Aaron Merey <amerey@redhat.com>]

On Wed, Feb 8, 2023 at 9:44 AM Tom Tromey <tom@tromey.com> wrote:
> It occurred to me last night that this could be a subtle change
> introduced by the pager rewrite.
>
> Before, disabling pagination also disabled line splitting, and took an
> earlier exit.
>
> But now, if pagination is disabled for some output, those lines still
> "count" towards the total.  So then when pagination is no longer
> disabled, a print might cause the pager to intervene.
>
> Is this what's happening in your case?  If so, I'm not totally sure it
> is a bug.  Normally disabling paging should be done because using the
> pager isn't safe or appropriate at some point in time.  But having those
> lines still "count" seems alright, maybe even useful.

Yes pagination_enabled=false prevents prompt_for_continue but lines_printed
still increments for each newline printed.

Like you said, this prompt shouldn't show up around debuginfod progress
output since most downloads happen under fetch_inferior_event which
disables pagination until it returns.

The reproducer I previously mentioned

On Mon, Jan 30, 2023 at 9:09 PM Aaron Merey <amerey@redhat.com> wrote:
>   gdb  -ex 'set height 25' -ex 'start' qemu-kvm

triggers the prompt during a download occurring right before 'start'
begins running the inferior and pagination isn't disabled by
fetch_inferior_event.

I don't think this particular case is too much of a problem because
there are only a few downloads that can happen before the rest occur
under fetch_inferior_event.  So the prompt will only show up at the
start if gdb's height is unusually small, in which case you can expect
regular prompts anyways.

However the on-demand downloading work creates new situations where
a large series of downloads might happen outside fetch_inferior_event.
For example, "break client.c:50" could download the .debug_line and
.debug_line_str of each shared library to search for the filename
"client.c". Then it downloads debuginfo for each match, all of which
happens outside of fetch_inferior_event.

Setting pagination_enabled=false in debuginfod_*_query prevents the
prompt durings the downloads but lines_printed keeps increasing.
If lines_allowed is exceeded then after the download you get an (IMO)
annoying prompt:

    (gdb) break client.c:50
    [...]
    Downloading separate debug info for /lib64/libabc.so
    Downloading separate debug info for /lib64/libxyz.so
    --Type <RET> for more, q to quit, c to continue without paging--
    Breakpoint 1 at 0xcf525d: client.c:50. (2 locations)
    (gdb)

Adding a count_lines_printed flag gives us another way to fine-tune
when the prompt shows up.  It keeps prompt behavior around debuginfod
output consistent whether or not the inferior is running.

Aaron