Re: [PATCH v2 6/6] migration: Deprecate fd: for file migration

The fd: URI can currently trigger two different types of migration, a TCP migration using sockets and a file migration using a plain file. This is in conflict with the recently introduced (8.2) QMP migrate API that takes structured data as JSON-like format. We cannot keep the same backend for both types of migration because with the new API the code is more tightly coupled to the type of transport. This means a TCP migration must use the 'socket' transport and a file migration must use the 'file' transport. If we keep allowing fd: when using a file, this creates an issue when the user converts the old-style (fd:) to the new style ("transport": "socket") invocation because the file descriptor in question has previously been allowed to be either a plain file or a socket. To avoid creating too much confusion, we can simply deprecate the fd: + file usage, which is thought to be rarely used currently and instead establish a 1:1 correspondence between fd: URI and socket transport, and file: URI and file transport. Signed-off-by: Fabiano Rosas <farosas(a)suse.de&gt; --- docs/about/deprecated.rst | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst index 0fb5c82640..813f7996fe 100644 --- a/docs/about/deprecated.rst +++ b/docs/about/deprecated.rst @@ -464,3 +464,17 @@ both, older and future versions of QEMU. The ``blacklist`` config file option has been renamed to ``block-rpcs`` (to be in sync with the renaming of the corresponding command line option). + +Migration +--------- + +``fd:`` URI when used for file migration (since 9.1) +'''''''''''''''''''''''''''''''''''''''''''''''''''' + +The ``fd:`` URI can currently provide a file descriptor that +references either a socket or a plain file. These are two different +types of migration. In order to reduce ambiguity, the ``fd:`` URI +usage of providing a file descriptor to a plain file has been +deprecated in favor of explicitly using the ``file:`` URI with the +file descriptor being passed as an ``fdset``. Refer to the ``add-fd`` +command documentation for details on the ``fdset`` usage.