Daniel P. Berrangé <berra...@redhat.com> writes: > On Mon, Oct 23, 2023 at 05:36:07PM -0300, Fabiano Rosas wrote: >> Add the direct-io migration parameter that tells the migration code to >> use O_DIRECT when opening the migration stream file whenever possible. >> >> This is currently only used for the secondary channels of fixed-ram >> migration, which can guarantee that writes are page aligned. > > When you say "secondary channels", I presume you're meaning that > the bulk memory regions will be written with O_DIRECT, while > general vmstate will use normal I/O on the main channel ? If so, > could we explain that a little more directly.
Yes, the main channel writes via QEMUFile, so no O_DIRECT. The channels created via multifd_new_send_channel_create() have O_DIRECT enabled. > Having a mixture of O_DIRECT and non-O_DIRECT I/O on the same > file is a little bit of an unusual situation. It will work for > us because we're writing to different regions of the file in > each case. > > Still I wonder if it would be sane in the outgoing case to > include a fsync() on the file in the main channel, to guarantee > that the whole saved file is on-media at completion ? Or perhaps > suggest in QAPI that mgmts might consider doing a fsync > themselves ? I think that should be present in QIOChannelFile in general. Not even related to this series. I'll add it at qio_channel_file_close() unless you object.
