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[Qemu-devel] [PULL v2 39/40] ivshmem: Require master to have ID zero
From: |
Markus Armbruster |
Subject: |
[Qemu-devel] [PULL v2 39/40] ivshmem: Require master to have ID zero |
Date: |
Mon, 21 Mar 2016 21:44:02 +0100 |
Migration with ivshmem needs to be carefully orchestrated to work.
Exactly one peer (the "master") migrates to the destination, all other
peers need to unplug (and disconnect), migrate, plug back (and
reconnect). This is sort of documented in qemu-doc.
If peers connect on the destination before migration completes, the
shared memory can get messed up. This isn't documented anywhere. Fix
that in qemu-doc.
To avoid messing up register IVPosition on migration, the server must
assign the same ID on source and destination. ivshmem-spec.txt leaves
ID assignment unspecified, however.
Amend ivshmem-spec.txt to require the first client to receive ID zero.
The example ivshmem-server complies: it always assigns the first
unused ID.
For a bit of additional safety, enforce ID zero for the master. This
does nothing when we're not using a server, because the ID is zero for
all peers then.
Signed-off-by: Markus Armbruster <address@hidden>
Reviewed-by: Marc-André Lureau <address@hidden>
Message-Id: <address@hidden>
---
docs/specs/ivshmem-spec.txt | 2 ++
hw/misc/ivshmem.c | 6 ++++++
qemu-doc.texi | 5 +++++
3 files changed, 13 insertions(+)
diff --git a/docs/specs/ivshmem-spec.txt b/docs/specs/ivshmem-spec.txt
index f3912c0..a1f5499 100644
--- a/docs/specs/ivshmem-spec.txt
+++ b/docs/specs/ivshmem-spec.txt
@@ -164,6 +164,8 @@ For each new client that connects to the server, the server
- sends interrupt setup messages to the new client (these contain file
descriptors for receiving interrupts).
+The first client to connect to the server receives ID zero.
+
When a client disconnects from the server, the server sends disconnect
notifications to the other clients.
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index 4552060..132387f 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -887,6 +887,12 @@ static void ivshmem_common_realize(PCIDevice *dev, Error
**errp)
return;
}
+ if (s->master == ON_OFF_AUTO_ON && s->vm_id != 0) {
+ error_setg(errp,
+ "master must connect to the server before any peers");
+ return;
+ }
+
qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive,
ivshmem_read, NULL, s);
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 0dd01c7..79141d3 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -1295,12 +1295,17 @@ When using the server, the guest will be assigned a VM
ID (>=0) that allows gues
using the same server to communicate via interrupts. Guests can read their
VM ID from a device register (see ivshmem-spec.txt).
address@hidden Migration with ivshmem
+
With device property @option{master=on}, the guest will copy the shared
memory on migration to the destination host. With @option{master=off},
the guest will not be able to migrate with the device attached. In the
latter case, the device should be detached and then reattached after
migration using the PCI hotplug support.
+At most one of the devices sharing the same memory can be master. The
+master must complete migration before you plug back the other devices.
+
@subsubsection ivshmem and hugepages
Instead of specifying the <shm size> using POSIX shm, you may specify
--
2.4.3
- [Qemu-devel] [PULL v2 15/40] ivshmem: Don't destroy the chardev on version mismatch, (continued)
- [Qemu-devel] [PULL v2 15/40] ivshmem: Don't destroy the chardev on version mismatch, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 24/40] ivshmem: Plug leaks on unplug, fix peer disconnect, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 20/40] ivshmem: Leave INTx alone when using MSI-X, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 27/40] ivshmem: Rely on server sending the ID right after the version, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 29/40] ivshmem: Simplify how we cope with short reads from server, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 31/40] ivshmem: Implement shm=... with a memory backend, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 35/40] ivshmem: Replace int role_val by OnOffAuto master, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 01/40] target-ppc: Document TOCTTOU in hugepage support, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 25/40] ivshmem: Receive shared memory synchronously in realize(), Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 10/40] ivshmem: Rewrite specification document, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 39/40] ivshmem: Require master to have ID zero,
Markus Armbruster <=
- [Qemu-devel] [PULL v2 03/40] ivshmem-server: Don't overload POSIX shmem and file name, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 19/40] ivshmem: Clean up MSI-X conditions, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 32/40] ivshmem: Simplify memory regions for BAR 2 (shared memory), Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 37/40] ivshmem: Clean up after the previous commit, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 26/40] ivshmem: Propagate errors through ivshmem_recv_setup(), Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 40/40] contrib/ivshmem-server: Print "not for production" warning, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 36/40] ivshmem: Split ivshmem-plain, ivshmem-doorbell off ivshmem, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 21/40] ivshmem: Assert interrupts are set up once, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 33/40] ivshmem: Inline check_shm_size() into its only caller, Markus Armbruster, 2016/03/21
- [Qemu-devel] [PULL v2 28/40] ivshmem: Drop the hackish test for UNIX domain chardev, Markus Armbruster, 2016/03/21