docs/specs/ivshmem-spec.rst

5 The Inter-VM shared memory device (ivshmem) is designed to share a
7 and the host.  In order for all guests to be able to pick up the
9 said memory to the guest as a PCI BAR.
35 There are two ways to use this device:
38   you have access to the shared memory in the guest and can use it as
41 - If you additionally need the capability for peers to interrupt each
42   other, you need BAR0 and BAR1.  You will most likely want to write a
43   kernel driver to handle interrupts.  Requires the device to be
50 IVPosition register (described below) to become non-negative before
53 Revision 0 of the device is not capable to tell guest software whether
95 There is no good way for software to find out whether the device is
99 Doorbell Register: writing this register requests to interrupt a peer.
100 The written value's high 16 bits are the ID of the peer to interrupt,
106 device is not capable to tell guest software whether setup is
107 complete.  Interrupts can regress to this state on migration.
111 capable to tell guest software what peers are connected, or how many
115 no way for software to clear the pending bit, and a polling mode of
119 Interrupt Status register is set to 1.  This asserts INTx unless
120 masked by the Interrupt Mask register.  The device is not capable to
121 communicate the interrupt vector to guest software then.
123 With multiple MSI-X vectors, different vectors can be used to indicate
125 are left to the application.
131 addition to shared memory.  The shared resources are managed by an
139 For each new client that connects to the server, the server
143 - sends the ID and the file descriptor for the shared memory to the
145 - sends connect notifications for the new client to the other clients
147 - sends connect notifications for the other clients to the new client,
149 - sends interrupt setup messages to the new client (these contain file
152 The first client to connect to the server receives ID zero.
155 notifications to the other clients.
160 its connected clients, the clients can elect to continue.  They can
163 no way for the clients to connect to a restarted server.  The device
164 is not capable to tell guest software whether the server is still up.
166 Example server code is in contrib/ivshmem-server/.  Not to be used in
176 An ivshmem device configured for interrupts connects to an ivshmem
179 The connection is one-way: the server sends messages to the client.
237 To interrupt a peer, the device writes the 8-byte integer 1 in native
238 byte order to the respective file descriptor.
240 To receive an interrupt, the device reads and discards as many 8-byte