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authorStefano Brivio <sbrivio@redhat.com>2021-08-26 14:37:48 +0200
committerStefano Brivio <sbrivio@redhat.com>2021-08-26 23:30:22 +0200
commitd2272f74f72469c3d4c2368439f36bb3b348db7c (patch)
tree29422c60ae49604c790134a0fea63a4171a05452 /util.c
parentcc2ebfd5f2c73b61590a28ff7d088520ce2c1502 (diff)
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tcp: Proper error handling for sendmmsg() to UNIX domain socket
As data from socket is forwarded to the guest, sendmmsg() might send fewer bytes than requested in three different ways: - failing altogether with a negative error code -- ignore that, we'll get an error on the UNIX domain socket later if there's really an issue with it and reset the connection to the guest - sending less than 'vlen' messages -- instead of assuming success in that case and waiting for the guest to send a duplicate ACK indicating missing data, update the sequence number according to what was actually sent and spare some retransmissions - somewhat unexpectedly to me, sending 'vlen' or less than 'vlen' messages, returning up to 'vlen', with the last message being partially sent, and no further indication of errors other than the returned msg_len for the last partially sent message being less than iov_len. In this case, we would assume success and proceed as nothing happened. However, qemu would fail to parse any further message, having received a partial descriptor, and eventually close the connection, logging: serious error: oversized packet received,connection terminated. as the length descriptor for the next message would be sourced from the middle of the next successfully sent message, not from its header. Handle this by checking the msg_len returned for the last (even partially) sent message, and force re-sending the missing bytes, if any, with a blocking sendmsg() -- qemu must not receive anything else than that anyway. While at it, allow to send up to 64KiB for each message, the previous 32KiB limit isn't actually required, and just switch to a new message at each iteration on sending buffers, they are already MSS-sized anyway, so the check in the loop isn't really needed. Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Diffstat (limited to 'util.c')
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