On incoming migration we have the following sequence to load option
ROM:
1. On device realize we do normal load ROM from the file
2. Than, on incoming migration we rewrite ROM from the incoming RAM
block. If sizes mismatch we fail, like this:
Size mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x40000 != 0x80000: Invalid argument
This is not ideal when we migrate to updated distribution: we have to
keep old ROM files in new distribution and be careful around romfile
property to load correct ROM file. Which is loaded actually just to
allocate the ROM with correct length.
Note, that romsize property doesn't really help: if we try to specify
it when default romfile is larger, it fails with something like:
romfile "efi-virtio.rom" (160768 bytes) is too large for ROM size 65536
Let's just ignore ROM file when romsize is specified and we are in
incoming migration state. In other words, we need only to preallocate
ROM of specified size, local ROM file is unrelated.
This way:
If romsize was specified on source, we just use same commandline as on
source, and migration will work independently of local ROM files on
target.
If romsize was not specified on source (and we have mismatching local
ROM file on target host), we have to specify romsize on target to match
source romsize. romfile parameter may be kept same as on source or may
be dropped, the file is not loaded anyway.
As a bonus we avoid extra reading from ROM file on target.
Note: when we don't have romsize parameter on source command line and
need it for target, it may be calculated as aligned up to power of two
size of ROM file on source (if we know, which file is it) or,
alternatively it may be retrieved from source QEMU by QMP qom-get
command, like
{ "execute": "qom-get",
"arguments": {
"path": "/machine/peripheral/CARD_ID/virtio-net-pci.rom[0]",
"property": "size" } }
Note: we have extra initialization of size variable to zero in
pci_add_option_rom to avoid false-positive
"error: ‘size’ may be used uninitialized"
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <20230522201740.88960-2-vsementsov@yandex-team.ru>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
8eb85fb5ac