Current logic assumes that channel connections on the destination side are always established in the same order as the source and the first one will always be the main channel followed by the multifid or post-copy preemption channel. This may not be always true, as even if a channel has a connection established on the source side it can be in the pending state on the destination side and a newer connection can be established first. Basically causing out of order mapping of channels on the destination side. Currently, all channels except post-copy preempt send a magic number, this patch uses that magic number to decide the type of channel. This logic is applicable only for precopy(multifd) live migration, as mentioned, the post-copy preempt channel does not send any magic number. Also, tls live migrations already does tls handshake before creating other channels, so this issue is not possible with tls, hence this logic is avoided for tls live migrations. This patch uses MSG_PEEK to check the magic number of channels so that current data/control stream management remains un-effected.
v2: TLS does not support MSG_PEEK, so V1 was broken for tls live migrations. For tls live migration, while initializing main channel tls handshake is done before we can create other channels, so this issue is not possible for tls live migrations. In V2 added a check to avoid checking magic number for tls live migration and fallback to older method to decide mapping of channels on destination side. v3: 1. Split change in two patches, io patch for read_peek routines, migration patch for migration related changes. 2. Add flags to io_readv calls to get extra read flags like MSG_PEEK. 3. Some other minor fixes. v4: 1. Removed common *all_eof routines for read peek and added one specific to live migration. 2. Updated to use qemu_co_sleep_ns instead of qio_channel_yield. 3. Some other minor fixes. v5: 1. Handle busy-wait in migration_channel_read_peek due partial reads. manish.mishra (2): io: Add support for MSG_PEEK for socket channel migration: check magic value for deciding the mapping of channels chardev/char-socket.c | 4 +-- include/io/channel.h | 6 ++++ io/channel-buffer.c | 1 + io/channel-command.c | 1 + io/channel-file.c | 1 + io/channel-null.c | 1 + io/channel-socket.c | 17 ++++++++++- io/channel-tls.c | 1 + io/channel-websock.c | 1 + io/channel.c | 16 +++++++--- migration/channel-block.c | 1 + migration/channel.c | 45 +++++++++++++++++++++++++++++ migration/channel.h | 5 ++++ migration/migration.c | 45 +++++++++++++++++++++-------- migration/multifd.c | 12 +++----- migration/multifd.h | 2 +- migration/postcopy-ram.c | 5 +--- migration/postcopy-ram.h | 2 +- scsi/qemu-pr-helper.c | 2 +- tests/qtest/tpm-emu.c | 2 +- tests/unit/test-io-channel-socket.c | 1 + util/vhost-user-server.c | 2 +- 22 files changed, 137 insertions(+), 36 deletions(-) -- 2.22.3