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[6/6] migration: Deprecate fd: for file migration

Message ID 20240425150939.19268-7-farosas@suse.de
State New
Headers show
Series migration removals & deprecations | expand

Commit Message

Fabiano Rosas April 25, 2024, 3:09 p.m. UTC 
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@suse.de>
---
 docs/about/deprecated.rst | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
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Patch

diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst
index fadb85f289..11dce324c8 100644
--- a/docs/about/deprecated.rst
+++ b/docs/about/deprecated.rst
@@ -484,3 +484,17 @@  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.