[patch] debuginfod metadata query timeout enforcement

[Aaron Merey]

Hi Frank,

On Tue, Sep 3, 2024 at 11:34 AM Frank Ch. Eigler <fche@elastic.org> wrote:
>
> Hi -
>
> Proposed patch for a problem we spotted recently in unreleased code:
>
> commit b853004e723d058f97362dbfdc40d1c49ea2ef51 (HEAD -> main)
> Author: Frank Ch. Eigler <fche@redhat.com>
> Date:   Tue Sep 3 11:27:36 2024 -0400
>
>     debuginfod: service metadata queries in separate, timed-out connections
>
>     The --metadata-maxtime=SECONDS parameter was intended to limit elapsed
>     time debuginfod spends attempting to answer metadata queries.  These
>     can be slow because they have to apply glob matches across a large set
>     of strings, potentially taking many seconds.
>
>     However, this option was not implemented fully.  It checked for
>     timeouts only when rows of data were finally served up by the
>     database, not during.  Also, it used the same database connection that
>     normal debuginfod queries were using, locking them out.
>
>     New code creates a new temporary database connection for these
>     infrequent(?)  metadata queries, and enforces timeouts using the
>     sqlite3 progress-handler callback.  This effectively limits total
>     query runtime, inside or outside the database.
>
>     The elfutils testsuite dataset is not large enough to show either the
>     slow-glob or the locking-out-normal-queries phenomenon, so the
>     behavioral impact was hand-tested on a moderate sized debuginfod index
>     on a live federation server.  A full valgrind leak check indicated
>     it's clean.
>
>     Signed-off-by: Frank Ch. Eigler <fche@redhat.com>

It isn't practical to add a testcase for this but you have rigorously
tested it by hand. LGTM.

Aaron