Send is conducted through qc_send_ppkts() for a QUIC connection. There
is two types of error which can be encountered on sendto() or affiliated
syscalls :
* transient error. In this case, sending is simulated with the remaining
data and retransmission process is used to have the opportunity to
retry emission
* fatal error. If this happens, the connection should be closed as soon
as possible. This is done via qc_kill_conn() function. Until this
patch, only ECONNREFUSED errno was considered as fatal.
Modify the QUIC send API to be able to differentiate transient and fatal
errors more easily. This is done by fixing the return value of the
sendto() wrapper qc_snd_buf() :
* on fatal error, a negative error code is returned. This is now the
case for every errno except EAGAIN, EWOULDBLOCK, ENOTCONN, EINPROGRESS
and EBADF.
* on a transient error, 0 is returned. This is the case for the listed
errno values above and also if a partial send has been conducted by
the kernel.
* on success, the return value of sendto() syscall is returned.
This commit will be useful to be able to handle transient error with a
quic-conn owned socket. In this case, the socket should be subscribed to
the poller and no simulated send will be conducted.
This commit allows errno management to be confined in the quic-sock
module which is a nice cleanup.
On a final note, EBADF should be considered as fatal. This will be the
subject of a next commit.
This should be backported up to 2.7.
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