From: "Alex Bennée" <alex.bennee@linaro.org>
To: qemu-devel@nongnu.org
Cc: richard.henderson@linaro.org,
"Alex Bennée" <alex.bennee@linaro.org>,
"Michael Tokarev" <mjt@tls.msk.ru>,
"Thomas Huth" <thuth@redhat.com>,
"Markus Armbruster" <armbru@redhat.com>,
"Kevin Wolf" <kwolf@redhat.com>
Subject: [PULL 06/18] qemu-options: finesse the recommendations around -blockdev
Date: Thu, 27 Apr 2023 16:44:58 +0100 [thread overview]
Message-ID: <20230427154510.1791273-7-alex.bennee@linaro.org> (raw)
In-Reply-To: <20230427154510.1791273-1-alex.bennee@linaro.org>
We are a bit premature in recommending -blockdev/-device as the best
way to configure block devices. It seems there are times the more
human friendly -drive still makes sense especially when -snapshot is
involved.
Improve the language to hopefully make things clearer.
Suggested-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230424092249.58552-7-alex.bennee@linaro.org>
diff --git a/qemu-options.hx b/qemu-options.hx
index 04c259157a..baa0589733 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1143,10 +1143,22 @@ have gone through several iterations as the feature set and complexity
of the block layer have grown. Many online guides to QEMU often
reference older and deprecated options, which can lead to confusion.
-The recommended modern way to describe disks is to use a combination of
+The most explicit way to describe disks is to use a combination of
``-device`` to specify the hardware device and ``-blockdev`` to
describe the backend. The device defines what the guest sees and the
-backend describes how QEMU handles the data.
+backend describes how QEMU handles the data. It is the only guaranteed
+stable interface for describing block devices and as such is
+recommended for management tools and scripting.
+
+The ``-drive`` option combines the device and backend into a single
+command line option which is a more human friendly. There is however no
+interface stability guarantee although some older board models still
+need updating to work with the modern blockdev forms.
+
+Older options like ``-hda`` are essentially macros which expand into
+``-drive`` options for various drive interfaces. The original forms
+bake in a lot of assumptions from the days when QEMU was emulating a
+legacy PC, they are not recommended for modern configurations.
ERST
@@ -1639,6 +1651,14 @@ SRST
the raw disk image you use is not written back. You can however
force the write back by pressing C-a s (see the :ref:`disk images`
chapter in the System Emulation Users Guide).
+
+ .. warning::
+ snapshot is incompatible with ``-blockdev`` (instead use qemu-img
+ to manually create snapshot images to attach to your blockdev).
+ If you have mixed ``-blockdev`` and ``-drive`` declarations you
+ can use the 'snapshot' property on your drive declarations
+ instead of this global option.
+
ERST
DEF("fsdev", HAS_ARG, QEMU_OPTION_fsdev,
--
2.39.2
next prev parent reply other threads:[~2023-04-27 15:45 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-27 15:44 [PULL 00/18] testing and doc updates Alex Bennée
2023-04-27 15:44 ` [PULL 01/18] tests/requirements.txt: bump up avocado-framework version to 101.0 Alex Bennée
2023-04-27 15:44 ` [PULL 02/18] tests/avocado: use the new snapshots for testing Alex Bennée
2023-04-28 12:08 ` Thomas Huth
2023-04-28 16:43 ` Alex Bennée
2023-04-27 15:44 ` [PULL 03/18] tests/avocado: Add set of boot tests on SBSA-ref Alex Bennée
2023-04-28 10:33 ` Thomas Huth
2023-07-10 12:10 ` Thomas Huth
2023-04-27 15:44 ` [PULL 04/18] gitlab-ci: Avoid to re-run "configure" in the device-crash-test jobs Alex Bennée
2023-04-27 15:44 ` [PULL 05/18] scripts/device-crash-test: Add a parameter to run with TCG only Alex Bennée
2023-04-27 15:44 ` Alex Bennée [this message]
2023-04-27 15:44 ` [PULL 07/18] .gitlab-ci.d/cirrus: Drop the CI job for compiling with FreeBSD 12 Alex Bennée
2023-04-27 15:45 ` [PULL 08/18] tests/avocado: Make ssh_command_output_contains() globally available Alex Bennée
2023-04-27 15:45 ` [PULL 09/18] tests/avocado/machine_aspeed: Fix the broken ast2[56]00_evb_sdk tests Alex Bennée
2023-04-27 15:45 ` [PULL 10/18] MAINTAINERS: Cover tests/avocado/machine_aspeed.py Alex Bennée
2023-04-27 15:45 ` [PULL 11/18] avocado_qemu/__init__.py: factor out the qemu-img finding Alex Bennée
2023-04-27 15:45 ` [PULL 12/18] tests/avocado/tuxrun_baselines.py: improve code coverage for ppc64 Alex Bennée
2023-04-27 15:45 ` [PULL 13/18] tests/tcg: limit the scope of the plugin tests Alex Bennée
2023-04-27 15:45 ` [PULL 14/18] qemu-options.hx: Update descriptions of memory options for NUMA node Alex Bennée
2023-04-27 15:45 ` [PULL 15/18] docs/system: remove excessive punctuation from guest-loader docs Alex Bennée
2023-04-27 15:45 ` [PULL 16/18] docs/devel: make a statement about includes Alex Bennée
2023-04-27 15:45 ` [PULL 17/18] docs/devel: mention the spacing requirement for QOM Alex Bennée
2023-04-27 15:45 ` [PULL 18/18] docs/style: call out the use of GUARD macros Alex Bennée
2023-04-28 7:34 ` [PULL 00/18] testing and doc updates Richard Henderson
2023-05-02 11:46 ` Peter Maydell
2023-05-02 12:21 ` Thomas Huth
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