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Diffstat (limited to 'docs/devel/migration/main.rst')
| -rw-r--r-- | docs/devel/migration/main.rst | 24 |
1 files changed, 19 insertions, 5 deletions
diff --git a/docs/devel/migration/main.rst b/docs/devel/migration/main.rst index 495cdcb112..784c899dca 100644 --- a/docs/devel/migration/main.rst +++ b/docs/devel/migration/main.rst @@ -47,11 +47,25 @@ over any transport. QEMU interference. Note that QEMU does not flush cached file data/metadata at the end of migration. -In addition, support is included for migration using RDMA, which -transports the page data using ``RDMA``, where the hardware takes care of -transporting the pages, and the load on the CPU is much lower. While the -internals of RDMA migration are a bit different, this isn't really visible -outside the RAM migration code. + The file migration also supports using a file that has already been + opened. A set of file descriptors is passed to QEMU via an "fdset" + (see add-fd QMP command documentation). This method allows a + management application to have control over the migration file + opening operation. There are, however, strict requirements to this + interface if the multifd capability is enabled: + + - the fdset must contain two file descriptors that are not + duplicates between themselves; + - if the direct-io capability is to be used, exactly one of the + file descriptors must have the O_DIRECT flag set; + - the file must be opened with WRONLY on the migration source side + and RDONLY on the migration destination side. + +- rdma migration: support is included for migration using RDMA, which + transports the page data using ``RDMA``, where the hardware takes + care of transporting the pages, and the load on the CPU is much + lower. While the internals of RDMA migration are a bit different, + this isn't really visible outside the RAM migration code. All these migration protocols use the same infrastructure to save/restore state devices. This infrastructure is shared with the |