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resolve: mention that dns_stream_update() needs to be called after dns_stream_take_read_packet()

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Based on the analysis by Joan Bruguera <joanbrugueram@gmail.com>.
See https://github.com/systemd/systemd/pull/22132#discussion_r793951650.
This commit is contained in:
Yu Watanabe 2022-01-28 09:01:07 +09:00
parent 624f907ea9
commit 4aa6129897
1 changed files with 7 additions and 0 deletions
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7
src/resolve/resolved-dns-stream.c
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@ -284,6 +284,13 @@ static int on_stream_timeout(sd_event_source *es, usec_t usec, void *userdata) {
static DnsPacket *dns_stream_take_read_packet(DnsStream *s) {
assert(s);
/* Note, dns_stream_update() should be called after this is called. When this is called, the
* stream may be already full and the EPOLLIN flag is dropped from the stream IO event source.
* Even this makes a room to read in the stream, this does not call dns_stream_update(), hence
* EPOLLIN flag is not set automatically. So, to read further packets from the stream,
* dns_stream_update() must be called explicitly. Currently, this is only called from
* on_stream_io_impl(), and there dns_stream_update() is called. */
if (!s->read_packet)
return NULL;