From a72f1c0f7b02ea571ec2ce35dfbe8c17c4dfa6d9 Mon Sep 17 00:00:00 2001

From: John Snow <jsnow@redhat.com>

Date: Thu, 11 May 2017 20:53:51 +0200

Subject: blockdev: ignore aio=native for empty drives

RH-Author: John Snow <jsnow@redhat.com>

Message-id: <20170511205351.6337-2-jsnow@redhat.com>

Patchwork-id: 75070

O-Subject: [RHV-7.4 qemu-kvm-rhev PATCH 1/1] blockdev: ignore aio=native for empty drives

Bugzilla: 1402645

RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

RH-Acked-by: Eric Blake <eblake@redhat.com>

RH-Acked-by: Max Reitz <mreitz@redhat.com>

This is a bit of a gross one; Upstream QEMU changed the way it handles

cache options with regards to removable media, associating options more

with the medium instead of the device. As part of that, it became

impossible to specify cache options on empty drives.

In the future, one would use blockdev-add instead to choose cache options

per-medium instead of per-device, but we're not there yet in libvirt so

we added a workaround downstream to simply ignore cache options on empty

CDROMs under the premise of "It actually never worked anyway."

As fallout from this decision, it is now no longer possible to specify

aio=native on empty CDROM devices either, as that requires the use of a

cache option that you can no longer specify. As a bad, gross, disgusting

workaround, simply ignore aio=native on empty drives until such time that

libvirt stops providing such configurations.

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

(cherry picked from commit cda174ad842c9a61bc275315bf3155139ba19bc0)

---

 blockdev.c | 17 ++++++++++++++++-

 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/blockdev.c b/blockdev.c

index 6d4cb70..d54ea6f 100644

--- a/blockdev.c

+++ b/blockdev.c

@@ -476,6 +476,21 @@ static bool __redhat_com_has_bs_opts(QDict *bs_opts)

     return s != n;

 }

+/**

+ * libvirt expects to be able to pass io driver options (aio=native) for CDROM

+ * drives without inserted media. While this has worked historically, given the

+ * above workaround and lack of a supported alternative in current versions of

+ * libvirt, certain options such as aio=native cannot be supported as it

+ * requires the use of an accompanying cache option, which we also ignore.

+ * Until libvirt learns how to supply cache options to inserted media, ignore

+ * the aio= preference on empty CDROMs with the understanding that un-tuned

+ * performance is preferable to being unable to use the CDROM at all.

+ */

+static int __redhat_com_filter_flags(int flags)

+{

+    return flags & ~BDRV_O_NATIVE_AIO;

+}

+

 /* Takes the ownership of bs_opts */

 static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,

                                    Error **errp)

@@ -588,7 +603,7 @@ static BlockBackend *blockdev_init(const char *file, QDict *bs_opts,

         blk = blk_new(0, BLK_PERM_ALL);

         blk_rs = blk_get_root_state(blk);

-        blk_rs->open_flags    = bdrv_flags;

+        blk_rs->open_flags    = __redhat_com_filter_flags(bdrv_flags);

         blk_rs->read_only     = read_only;

         blk_rs->detect_zeroes = detect_zeroes;

-- 

1.8.3.1