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[PATCH v8.0.1 07/36] qemu-options: finesse the recommendations around -b
From: |
Michael Tokarev |
Subject: |
[PATCH v8.0.1 07/36] qemu-options: finesse the recommendations around -blockdev |
Date: |
Wed, 17 May 2023 11:00:27 +0300 |
From: Alex Bennée <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>
(cherry picked from commit c1654c3e37c31fb638597efedcd07d071837b78b)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
qemu-options.hx | 24 ++++++++++++++++++++++--
1 file changed, 22 insertions(+), 2 deletions(-)
diff --git a/qemu-options.hx b/qemu-options.hx
index 59bdf67a2c..4b8855a4f7 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
- [PATCH v8.0.1 00/36] Patch Round-up for stable 8.0.1, freeze on 2023-05-27, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 03/36] hw/timer/imx_epit: don't shadow variable, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 02/36] target/i386: Change wrong XFRM value in SGX CPUID leaf, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 09/36] target/arm: Initialize debug capabilities only once, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 06/36] block/monitor: Fix crash when executing HMP commit, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 12/36] hw/arm/aspeed: Use arm_write_bootloader() to write the bootloader, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 01/36] vnc: avoid underflow when accessing user-provided address, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 04/36] hw/timer/imx_epit: fix limit check, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 08/36] docs/about/deprecated.rst: Add "since 7.1" tag to dtb-kaslr-seed deprecation, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 10/36] hw/net/msf2-emac: Don't modify descriptor in-place in emac_store_desc(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 07/36] qemu-options: finesse the recommendations around -blockdev,
Michael Tokarev <=
- [PATCH v8.0.1 05/36] acpi: pcihp: allow repeating hot-unplug requests, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 11/36] hw/arm/boot: Make write_bootloader() public as arm_write_bootloader(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 16/36] hw/sd/allwinner-sdhost: Correctly byteswap descriptor fields, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 23/36] block: bdrv/blk_co_unref() for calls in coroutine context, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 14/36] hw/intc/allwinner-a10-pic: Don't use set_bit()/clear_bit(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 22/36] block: Consistently call bdrv_activate() outside coroutine, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 20/36] meson: leave unnecessary modules out of the build, Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 18/36] block/export: call blk_set_dev_ops(blk, NULL, NULL), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 21/36] block: Fix use after free in blockdev_mark_auto_del(), Michael Tokarev, 2023/05/17
- [PATCH v8.0.1 15/36] target/arm: Define and use new load_cpu_field_low32(), Michael Tokarev, 2023/05/17