2aaf6bb6e9
When sending multiple DNS questions to a DNS-over-TLS server (e.g. a question for A and AAAA records, as is typical) on the same session, the server may answer to each question in a separate TLS record, but it may also aggregate multiple answers in a single TLS record. (Some servers do this very often (e.g. Cloudflare 1.0.0.1), some do it sometimes (e.g. Google 8.8.8.8) and some seem to never do it (e.g. Quad9 9.9.9.10)). Both cases should be handled equivalently, as the byte stream is the same, but when multiple answers came in a single TLS record, usually the first answer was processed, but the second answer was entirely ignored, which caused a 10s delay until the resolution timed out and the missing question was retried. This can be reproduced by configuring one of the offending server and running `resolvectl query google.com --cache=no` a few times. To be notified of incoming data, systemd-resolved listens to `EPOLLIN` events on the underlying socket. However, when DNS-over-TLS is used, the TLS library (OpenSSL or GnuTLS) may read and buffer the entire TLS record when reading the first answer, so usually no further `EPOLLIN` events will be generated, and the second answer will never be processed. To avoid this, if there's buffered TLS data, generate a "fake" EPOLLIN event. This is hacky, but it makes this case transparent to the rest of the IO code.
System and Service Manager
Details
Most documentation is available on systemd's web site.
Assorted, older, general information about systemd can be found in the systemd Wiki.
Information about build requirements is provided in the README file.
Consult our NEWS file for information about what's new in the most recent systemd versions.
Please see the Code Map for information about this repository's layout and content.
Please see the Hacking guide for information on how to hack on systemd and test your modifications.
Please see our Contribution Guidelines for more information about filing GitHub Issues and posting GitHub Pull Requests.
When preparing patches for systemd, please follow our Coding Style Guidelines.
If you are looking for support, please contact our mailing list or join our IRC channel.
Stable branches with backported patches are available in the stable repo.