Blame SOURCES/0026-blockdev-ignore-aio-native-for-empty-drives.patch

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From d4fe1e7fd6002d201088870c1e019b607c168454 Mon Sep 17 00:00:00 2001
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From: John Snow <jsnow@redhat.com>
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Date: Thu, 11 May 2017 20:53:51 +0200
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Subject: blockdev: ignore aio=native for empty drives
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RH-Author: John Snow <jsnow@redhat.com>
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Message-id: <20170511205351.6337-2-jsnow@redhat.com>
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Patchwork-id: 75070
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O-Subject: [RHV-7.4 qemu-kvm-rhev PATCH 1/1] blockdev: ignore aio=native for empty drives
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Bugzilla: 1402645
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RH-Acked-by: Kevin Wolf <kwolf@redhat.com>
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Max Reitz <mreitz@redhat.com>
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This is a bit of a gross one; Upstream QEMU changed the way it handles
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cache options with regards to removable media, associating options more
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with the medium instead of the device. As part of that, it became
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impossible to specify cache options on empty drives.
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In the future, one would use blockdev-add instead to choose cache options
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per-medium instead of per-device, but we're not there yet in libvirt so
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we added a workaround downstream to simply ignore cache options on empty
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CDROMs under the premise of "It actually never worked anyway."
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As fallout from this decision, it is now no longer possible to specify
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aio=native on empty CDROM devices either, as that requires the use of a
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cache option that you can no longer specify. As a bad, gross, disgusting
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workaround, simply ignore aio=native on empty drives until such time that
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libvirt stops providing such configurations.
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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(cherry picked from commit cda174ad842c9a61bc275315bf3155139ba19bc0)
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(cherry picked from commit a72f1c0f7b02ea571ec2ce35dfbe8c17c4dfa6d9)
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(cherry picked from commit 313ffb6aba9419fe620b898c9b4a5ab4b0bff205)
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(cherry picked from commit fa1666d4f59412a324067a1bd9b4fed7ca8c71f2)
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(cherry picked from commit 62a7f6391872a32c3fdcbce988e2b7b760fca0c9)
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---
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 blockdev.c | 17 ++++++++++++++++-
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 1 file changed, 16 insertions(+), 1 deletion(-)
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diff --git a/blockdev.c b/blockdev.c
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index cf10108..60b37dc 100644
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--- a/blockdev.c
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+++ b/blockdev.c
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@@ -486,6 +486,21 @@ static bool __redhat_com_has_bs_opts(QDict *bs_opts)
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     return s != n;
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 }
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+/**
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+ * libvirt expects to be able to pass io driver options (aio=native) for CDROM
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+ * drives without inserted media. While this has worked historically, given the
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+ * above workaround and lack of a supported alternative in current versions of
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+ * libvirt, certain options such as aio=native cannot be supported as it
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+ * requires the use of an accompanying cache option, which we also ignore.
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+ * Until libvirt learns how to supply cache options to inserted media, ignore
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+ * the aio= preference on empty CDROMs with the understanding that un-tuned
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+ * performance is preferable to being unable to use the CDROM at all.
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+ */
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+static int __redhat_com_filter_flags(int flags)
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+{
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+    return flags & ~BDRV_O_NATIVE_AIO;
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+}
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+
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 /* Takes the ownership of bs_opts */
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 static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
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                                    Error **errp)
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@@ -598,7 +613,7 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,
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         blk = blk_new(0, BLK_PERM_ALL);
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         blk_rs = blk_get_root_state(blk);
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-        blk_rs->open_flags    = bdrv_flags;
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+        blk_rs->open_flags    = __redhat_com_filter_flags(bdrv_flags);
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         blk_rs->read_only     = read_only;
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         blk_rs->detect_zeroes = detect_zeroes;
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-- 
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1.8.3.1
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