The src flush condition check is over complicated, and it's getting more
out of control if postcopy will be involved.
In general, we have two modes to do the sync: legacy or modern ways.
Legacy uses per-section flush, modern uses per-round flush.
Mapped-ram always uses the modern, which is per-round.
Introduce two helpers, which can greatly simplify the code, and hopefully
make it readable again.
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241206224755.1108686-7-peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
RAM_SAVE_FLAG_MULTIFD_FLUSH message should always be correlated to a sync
request on src. Unify such message into one place, and conditionally send
the message only if necessary.
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20241206224755.1108686-5-peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Teach multifd_send_sync_main() to sync with threads only.
We already have such requests, which is when mapped-ram is enabled with
multifd. In that case, no SYNC messages will be pushed to the stream when
multifd syncs the sender threads because there's no destination threads
waiting for that. The whole point of the sync is to make sure all threads
finished their jobs.
So fundamentally we have a request to do the sync in different ways:
- Either to sync the threads only,
- Or to sync the threads but also with the destination side.
Mapped-ram did it already because of the use_packet check in the sync
handler of the sender thread. It works.
However it may stop working when e.g. VFIO may start to reuse multifd
channels to push device states. In that case VFIO has similar request on
"thread-only sync" however we can't check a flag because such sync request
can still come from RAM which needs the on-wire notifications.
Paving way for that by allowing the multifd_send_sync_main() to specify
what kind of sync the caller needs. We can use it for mapped-ram already.
No functional change intended.
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-Id: <20241206224755.1108686-3-peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Coverity points out that the current usage of strncpy to write the
ramblock name allows the field to not have an ending '\0' in case
idstr is already not null-terminated (e.g. if it's larger than 256
bytes).
This is currently harmless because the packet->ramblock field is never
touched again on the source side. The destination side reads only up
to the field's size from the stream and forces the last byte to be 0.
We're still open to a programming error in the future in case this
field is ever passed into a function that expects a null-terminated
string.
Change from strncpy to QEMU's pstrcpy, which puts a '\0' at the end of
the string and doesn't fill the extra space with zeros.
(there's no spillage between iterations of fill_packet because after
commit 87bb9e953e ("migration/multifd: Isolate ram pages packet data")
the packet is always zeroed before filling)
Resolves: Coverity CID 1560071
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240919150611.17074-1-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
As observed by Philippe, the multifd_ram_unfill_packet() function
currently leaves the MultiFDPacket structure with mixed
endianness. This is harmless, but ultimately not very clean.
Stop touching the received packet and do the necessary work using
stack variables instead.
While here tweak the error strings and fix the space before
semicolons. Also remove the "100 times bigger" comment because it's
just one possible explanation for a size mismatch and it doesn't even
match the code.
CC: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
The methods are defined at module_init time and don't ever
change. Make them const.
Suggested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
In preparation for adding new payload types to multifd, move most of
the no-compression code into multifd-nocomp.c. Let's try to keep a
semblance of layering by not mixing general multifd control flow with
the details of transmitting pages of ram.
There are still some pieces leftover, namely the p->normal, p->zero,
etc variables that we use for zero page tracking and the packet
allocation which is heavily dependent on the ram code.
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
