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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [DOC v7] PV Calls protocol design
Upon request from Konrad, I am attaching the output of pahole on the C
structs defined by PVCalls. As you can see, alignments and sizes of all
fields are the same, except for the padding at the end of many request
structs (they need to be multiple of 8 bytes on 64bit). However, struct
xen_pvcalls_dummy dummy ensures that the overall size of struct
xen_pvcalls_request is the same on both 32 and 64.
On Thu, 13 Oct 2016, Stefano Stabellini wrote:
> Hi all,
>
> This is the design document of the PV Calls protocol. You can find
> prototypes of the Linux frontend and backend drivers here:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/sstabellini/xen.git pvcalls-7
>
> To use them, make sure to enable CONFIG_XEN_PVCALLS in your kernel
> config and add "pvcalls=1" to the command line of your DomU Linux
> kernel. You also need the toolstack to create the initial xenstore nodes
> for the protocol. To do that, please apply the attached patch to libxl
> (the patch is based on Xen 4.7.0-rc3) and add "pvcalls=1" to your DomU
> config file.
>
> Please review!
>
> Cheers,
>
> Stefano
>
>
> Changes in v7:
> - add a glossary of Xen terms
> - add a paragraph on why Xen was chosen
> - wording improvements
> - add links to xenstore documents and headers
> - specify that the current version is "1"
> - rename max-dataring-page-order to max-page-order
> - rename networking-calls to function-calls
> - add links to [Data ring] throughout the document
> - explain the difference between req_id and id
> - mention that future commands larger than 56 bytes will require a
> version increase
> - mention that the list of commands is in calling order
> - clarify that reuse data rings are found by ref
> - rename ENOTSUPP to ENOTSUP
> - add padding in struct pvcalls_data_intf for cachelining
> - rename pvcalls_ring_queued to pvcalls_ring_unconsumed
>
>
> Changes in v6:
> - add reuse field in release command
> - add "networking-calls" backend node on xenstore
> - fixed tab/whitespace indentation
>
> Changes in v5:
> - clarify text
> - rename id to req_id
> - rename sockid to id
> - move id to request and response specific fields
> - add version node to xenstore
>
> Changes in v4:
> - rename xensock to pvcalls
>
> Changes in v3:
> - add a dummy element to struct xen_xensock_request to make sure the
> size of the struct is the same on both x86_32 and x86_64
>
> Changes in v2:
> - add max-dataring-page-order
> - add "Publish backend features and transport parameters" to backend
> xenbus workflow
> - update new cmd values
> - update xen_xensock_request
> - add backlog parameter to listen and binary layout
> - add description of new data ring format (interface+data)
> - modify connect and accept to reflect new data ring format
> - add link to POSIX docs
> - add error numbers
> - add address format section and relevant numeric definitions
> - add explicit mention of unimplemented commands
> - add protocol node name
> - add xenbus shutdown diagram
> - add socket operation
>
> ---
>
>
> # PV Calls Protocol version 1
>
> ## Glossary
>
> The following is a list of terms and definitions used in the Xen
> community. If you are a Xen contributor you can skip this section.
>
> * PV
>
> Short for paravirtualized.
>
> * Dom0
>
> First virtual machine that boots. In most configurations Dom0 is
> privileged and has control over hardware devices, such as network
> cards, graphic cards, etc.
>
> * DomU
>
> Regular unprivileged Xen virtual machine.
>
> * Domain
>
> A Xen virtual machine. Dom0 and all DomUs are all separate Xen
> domains.
>
> * Guest
>
> Same as domain: a Xen virtual machine.
>
> * Frontend
>
> Each DomU has one or more paravirtualized frontend drivers to access
> disks, network, console, graphics, etc. The presence of PV devices is
> advertized on XenStore, a cross domain key-value database. Frontends
> are similar in intent to the virtio drivers in Linux.
>
> * Backend
>
> A Xen paravirtualized backend typically runs in Dom0 and it is used to
> export disks, network, console, graphics, etcs, to DomUs. Backends can
> live both in kernel space and in userspace. For example xen-blkback
> lives under drivers/block in the Linux kernel and xen_disk lives under
> hw/block in QEMU. Paravirtualized backends are similar in intent to
> virtio device emulators.
>
> * VMX and SVM
>
> On Intel processors, VMX is the CPU flag for VT-x, hardware
> virtualization support. It corresponds to SVM on AMD processors.
>
>
>
> ## Rationale
>
> PV Calls is a paravirtualized protocol that allows the implementation of
> a set of POSIX functions in a different domain. The PV Calls frontend
> sends POSIX function calls to the backend, which implements them and
> returns a value to the frontend.
>
> This version of the document covers networking function calls, such as
> connect, accept, bind, release, listen, poll, recvmsg and sendmsg; but
> the protocol is meant to be easily extended to cover different sets of
> calls. Unimplemented commands return ENOTSUP.
>
> PV Calls provide the following benefits:
> * full visibility of the guest behavior on the backend domain, allowing
> for inexpensive filtering and manipulation of any guest calls
> * excellent performance
>
> Specifically, PV Calls for networking offer these advantages:
> * guest networking works out of the box with VPNs, wireless networks and
> any other complex configurations on the host
> * guest services listen on ports bound directly to the backend domain IP
> addresses
> * localhost becomes a secure namespace for inter-VMs communications
>
>
> ## Design
>
> ### Why Xen?
>
> PV Calls are part of an effort to create a secure runtime environment
> for containers (OCI images to be precise). PV Calls are based on Xen,
> although porting them to other hypervisors is possible. Xen was chosen
> because of its security and isolation properties and because it supports
> PV guests, a type of virtual machines that does not require hardware
> virtualization extensions (VMX on Intel processors and SVM on AMD
> processors). This is important because PV Calls is meant for containers
> and containers are often run on top of public cloud instances, which do
> not support nested VMX (or SVM) as of today (late 2016). Xen PV guests
> are lightweight, minimalist, and do not require machine emulation: all
> properties that make them a good fit for the project.
>
> ### Xenstore
>
> The frontend and the backend connect via [xenstore] to
> exchange information. The toolstack creates front and back nodes with
> state [XenbusStateInitialising]. The protocol node name
> is **pvcalls**. There can only be one PV Calls frontend per domain.
>
> #### Frontend XenBus Nodes
>
> port
> Values: <uint32_t>
>
> The identifier of the Xen event channel used to signal activity
> in the ring buffer.
>
> ring-ref
> Values: <uint32_t>
>
> The Xen grant reference granting permission for the backend to map
> the sole page in a single page sized ring buffer. Later on this
> ring will be referred to commands ring.
>
> #### Backend XenBus Nodes
>
> version
> Values: <uint32_t>
>
> Protocol version supported by the backend. Currently the value is
> 1.
>
> max-page-order
> Values: <uint32_t>
>
> The maximum supported size of a memory allocation in units of
> lb(machine pages), e.g. 0 == 1 page, 1 = 2 pages, 2 == 4 pages,
> etc.
>
> function-calls
> Values: <uint32_t>
>
> Value "0" means that no calls are supported.
> Value "1" means that socket, connect, release, bind, listen, accept
> and poll are supported.
>
> #### State Machine
>
> Initialization:
>
> *Front* *Back*
> XenbusStateInitialising XenbusStateInitialising
> - Query virtual device - Query backend device
> properties. identification data.
> - Setup OS device instance. - Publish backend features
> - Allocate and initialize the and transport parameters
> request ring. |
> - Publish transport parameters |
> that will be in effect during V
> this connection. XenbusStateInitWait
> |
> |
> V
> XenbusStateInitialised
>
> - Query frontend transport
> parameters.
> - Connect to the request ring and
> event channel.
> |
> |
> V
> XenbusStateConnected
>
> - Query backend device properties.
> - Finalize OS virtual device
> instance.
> |
> |
> V
> XenbusStateConnected
>
> Once frontend and backend are connected, they have a shared page, which
> will is used to exchange messages over a ring, and an event channel,
> which is used to send notifications.
>
> Shutdown:
>
> *Front* *Back*
> XenbusStateConnected XenbusStateConnected
> |
> |
> V
> XenbusStateClosing
>
> - Unmap grants
> - Unbind evtchns
> |
> |
> V
> XenbusStateClosing
>
> - Unbind evtchns
> - Free rings
> - Free data structures
> |
> |
> V
> XenbusStateClosed
>
> - Free remaining data structures
> |
> |
> V
> XenbusStateClosed
>
>
> ### Commands Ring
>
> The shared ring is used by the frontend to forward POSIX function calls
> to the backend. We shall refer to this ring as **commands ring** to
> distinguish it from other rings which can be created later in the
> lifecycle of the protocol (see [Data ring]). The grant reference for
> shared page for this ring is shared on xenstore (see [Frontend XenBus
> Nodes]). The ring format is defined using the familiar
> `DEFINE_RING_TYPES` macro (`xen/include/public/io/ring.h`). Frontend
> requests are allocated on the ring using the `RING_GET_REQUEST` macro.
> The list of commands below is in calling order.
>
> The format is defined as follows:
>
> #define PVCALLS_SOCKET 0
> #define PVCALLS_CONNECT 1
> #define PVCALLS_RELEASE 2
> #define PVCALLS_BIND 3
> #define PVCALLS_LISTEN 4
> #define PVCALLS_ACCEPT 5
> #define PVCALLS_POLL 6
>
> struct xen_pvcalls_request {
> uint32_t req_id; /* private to guest, echoed in response */
> uint32_t cmd; /* command to execute */
> union {
> struct xen_pvcalls_socket {
> uint64_t id;
> uint32_t domain;
> uint32_t type;
> uint32_t protocol;
> } socket;
> struct xen_pvcalls_connect {
> uint64_t id;
> uint8_t addr[28];
> uint32_t len;
> uint32_t flags;
> grant_ref_t ref;
> uint32_t evtchn;
> } connect;
> struct xen_pvcalls_release {
> uint64_t id;
> uint8_t reuse;
> } release;
> struct xen_pvcalls_bind {
> uint64_t id;
> uint8_t addr[28];
> uint32_t len;
> } bind;
> struct xen_pvcalls_listen {
> uint64_t id;
> uint32_t backlog;
> } listen;
> struct xen_pvcalls_accept {
> uint64_t id;
> uint64_t id_new;
> grant_ref_t ref;
> uint32_t evtchn;
> } accept;
> struct xen_pvcalls_poll {
> uint64_t id;
> } poll;
> /* dummy member to force sizeof(struct xen_pvcalls_request) to
> match across archs */
> struct xen_pvcalls_dummy {
> uint8_t dummy[56];
> } dummy;
> } u;
> };
>
> The first two fields are common for every command. Their binary layout
> is:
>
> 0 4 8
> +-------+-------+
> |req_id | cmd |
> +-------+-------+
>
> - **req_id** is generated by the frontend and is a cookie used to
> identify one specific request/response pair of commands. Not to be
> confused with any command **id** which are used to identify a socket
> across multiple commands, see [Socket].
> - **cmd** is the command requested by the frontend:
>
> - `PVCALLS_SOCKET`: 0
> - `PVCALLS_CONNECT`: 1
> - `PVCALLS_RELEASE`: 2
> - `PVCALLS_BIND`: 3
> - `PVCALLS_LISTEN`: 4
> - `PVCALLS_ACCEPT`: 5
> - `PVCALLS_POLL`: 6
>
> Both fields are echoed back by the backend. See [Socket families and
> address format] for the format of the **addr** field of connect and
> bind. The maximum size of command specific arguments is 56 bytes. Any
> future command that requires more than that will need a bump the
> **version** of the protocol.
>
> Similarly to other Xen ring based protocols, after writing a request to
> the ring, the frontend calls `RING_PUSH_REQUESTS_AND_CHECK_NOTIFY` and
> issues an event channel notification when a notification is required.
>
> Backend responses are allocated on the ring using the `RING_GET_RESPONSE`
> macro.
> The format is the following:
>
> struct xen_pvcalls_response {
> uint32_t req_id;
> uint32_t cmd;
> int32_t ret;
> uint32_t pad;
> union {
> struct _xen_pvcalls_socket {
> uint64_t id;
> } socket;
> struct _xen_pvcalls_connect {
> uint64_t id;
> } connect;
> struct _xen_pvcalls_release {
> uint64_t id;
> } release;
> struct _xen_pvcalls_bind {
> uint64_t id;
> } bind;
> struct _xen_pvcalls_listen {
> uint64_t id;
> } listen;
> struct _xen_pvcalls_accept {
> uint64_t id;
> } accept;
> struct _xen_pvcalls_poll {
> uint64_t id;
> } poll;
> struct _xen_pvcalls_dummy {
> uint8_t dummy[8];
> } dummy;
> } u;
> };
>
> The first four fields are common for every response. Their binary layout
> is:
>
> 0 4 8 12 16
> +-------+-------+-------+-------+
> |req_id | cmd | ret | pad |
> +-------+-------+-------+-------+
>
> - **req_id**: echoed back from request
> - **cmd**: echoed back from request
> - **ret**: return value, identifies success (0) or failure (see error numbers
> below). If the **cmd** is not supported by the backend, ret is ENOTSUP.
> - **pad**: padding
>
> After calling `RING_PUSH_RESPONSES_AND_CHECK_NOTIFY`, the backend checks
> whether
> it needs to notify the frontend and does so via event channel.
>
> A description of each command, their additional request and response
> fields follow.
>
>
> #### Socket
>
> The **socket** operation corresponds to the POSIX [socket][socket]
> function. It creates a new socket of the specified family, type and
> protocol. **id** is freely chosen by the frontend and references this
> specific socket from this point forward. See "Socket families and
> address format" below.
>
> Request fields:
>
> - **cmd** value: 0
> - additional fields:
> - **id**: generated by the frontend, it identifies the new socket
> - **domain**: the communication domain
> - **type**: the socket type
> - **protocol**: the particular protocol to be used with the socket, usually > 0
>
> Request binary layout:
>
> 8 12 16 20 24 28
> +-------+-------+-------+-------+-------+
> | id |domain | type |protoco|
> +-------+-------+-------+-------+-------+
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+--------+
> | id |
> +-------+--------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX socket function][connect] for error names; the
> corresponding
> error numbers are specified later in this document.
>
> #### Connect
>
> The **connect** operation corresponds to the POSIX [connect][connect]
> function. It connects a previously created socket (identified by **id**)
> to the specified address.
>
> The connect operation creates a new shared ring, which we'll call **data
> ring**. The [Data ring] is used to send and receive data from the
> socket. The connect operation passes two additional parameters:
> **evtchn** and **ref**. **evtchn** is the port number of a new event
> channel which will be used for notifications of activity on the data
> ring. **ref** is the grant reference of a page which contains shared
> indices that point to the write and read locations in the ring buffers.
> **ref** also contains the full array of grant references for the ring
> buffers. When the frontend issues a **connect** command, the backend:
>
> - finds its own internal socket corresponding to **id**
> - connects the socket to **addr**
> - maps the grant reference **ref**, the shared page contains the data
> ring interface (`struct pvcalls_data_intf`)
> - maps all the grant references listed in `struct pvcalls_data_intf` and
> uses them as shared memory for the ring buffers
> - bind the **evtchn**
> - replies to the frontend
>
> The [Data ring] format will be described in the following section. The
> data ring is unmapped and freed upon issuing a **release** command on
> the active socket identified by **id**.
>
> Request fields:
>
> - **cmd** value: 0
> - additional fields:
> - **id**: identifies the socket
> - **addr**: address to connect to, see the address format section for more
> information
> - **len**: address length
> - **flags**: flags for the connection, reserved for future usage
> - **ref**: grant reference of the page containing `struct
> pvcalls_data_intf`
> - **evtchn**: port number of the evtchn to signal activity on the data ring
>
> Request binary layout:
>
> 8 12 16 20 24 28 32 36 40 44
> +-------+-------+-------+-------+-------+-------+-------+-------+-------+
> | id | addr |
> +-------+-------+-------+-------+-------+-------+-------+-------+-------+
> | len | flags | ref |evtchn |
> +-------+-------+-------+-------+
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+-------+
> | id |
> +-------+-------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX connect function][connect] for error names; the
> corresponding
> error numbers are specified later in this document.
>
> #### Release
>
> The **release** operation closes an existing active or a passive socket.
>
> When a release command is issued on a passive socket, the backend
> releases it and frees its internal mappings. When a release command is
> issued for an active socket, the data ring is also unmapped and freed:
>
> - frontend sends release command for an active socket
> - backend releases the socket
> - backend unmaps the data ring buffers
> - backend unmaps the data ring interface
> - backend unbinds the evtchn
> - backend replies to frontend
> - frontend frees ring and unbinds evtchn
>
> Request fields:
>
> - **cmd** value: 1
> - additional fields:
> - **id**: identifies the socket
> - **reuse**: an optimization hint for the backend. The field is
> ignored for passive sockets. When set to 1, the frontend lets the
> backend know that it will reuse exactly the same set of grant pages
> (interface and data ring) and evtchn when creating one of the next
> active sockets. The backend can take advantage of it by delaying
> unmapping grants and unbinding the evtchn. The backend is free to
> ignore the hint. Reused data rings are found by **ref**, the grant
> reference of the page containing the indices.
>
> Request binary layout:
>
> 8 12 16 17
> +-------+-------+-----+
> | id |reuse|
> +-------+-------+-----+
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+-------+
> | id |
> +-------+-------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX shutdown function][shutdown] for error names; the
> corresponding error numbers are specified later in this document.
>
> #### Bind
>
> The **bind** operation corresponds to the POSIX [bind][bind] function.
> It assigns the address passed as parameter to a previously created
> socket, identified by **id**. **Bind**, **listen** and **accept** are
> the three operations required to have fully working passive sockets and
> should be issued in this order.
>
> Request fields:
>
> - **cmd** value: 2
> - additional fields:
> - **id**: identifies the socket
> - **addr**: address to connect to, see the address format section for more
> information
> - **len**: address length
>
> Request binary layout:
>
> 8 12 16 20 24 28 32 36 40 44
> +-------+-------+-------+-------+-------+-------+-------+-------+-------+
> | id | addr |
> +-------+-------+-------+-------+-------+-------+-------+-------+-------+
> | len |
> +-------+
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+-------+
> | id |
> +-------+-------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX bind function][bind] for error names; the corresponding
> error
> numbers are specified later in this document.
>
>
> #### Listen
>
> The **listen** operation marks the socket as a passive socket. It corresponds
> to
> the [POSIX listen function][listen].
>
> Reuqest fields:
>
> - **cmd** value: 3
> - additional fields:
> - **id**: identifies the socket
> - **backlog**: the maximum length to which the queue of pending
> connections may grow
>
> Request binary layout:
>
> 8 12 16 20
> +-------+-------+-------+
> | id |backlog|
> +-------+-------+-------+
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+-------+
> | id |
> +-------+-------+
>
> Return value:
> - 0 on success
> - See the [POSIX listen function][listen] for error names; the corresponding
> error numbers are specified later in this document.
>
>
> #### Accept
>
> The **accept** operation extracts the first connection request on the
> queue of pending connections for the listening socket identified by
> **id** and creates a new connected socket. The id of the new socket is
> also chosen by the frontend and passed as an additional field of the
> accept request struct (**id_new**). See the [POSIX accept function][accept]
> as reference.
>
> Similarly to the **connect** operation, **accept** creates a new [Data
> ring]. The data ring is used to send and receive data from the socket.
> The **accept** operation passes two additional parameters: **evtchn**
> and **ref**. **evtchn** is the port number of a new event channel which
> will be used for notifications of activity on the data ring. **ref** is
> the grant reference of a page which contains shared indices that point
> to the write and read locations in the ring buffers. **ref** also
> contains the full array of grant references for the ring buffers.
>
> The backend will reply to the request only when a new connection is
> successfully accepted, i.e. the backend does not return EAGAIN or
> EWOULDBLOCK.
>
> Example workflow:
>
> - frontend issues an **accept** request
> - backend waits for a connection to be available on the socket
> - a new connection becomes available
> - backend accepts the new connection
> - backend creates an internal mapping from **id_new** to the new socket
> - backend maps the grant reference **ref**, the shared page contains the
> data ring interface (`struct pvcalls_data_intf`)
> - backend maps all the grant references listed in `struct
> pvcalls_data_intf` and uses them as shared memory for the new data
> ring
> - backend binds the **evtchn**
> - backend replies to the frontend
>
> Request fields:
>
> - **cmd** value: 4
> - additional fields:
> - **id**: id of listening socket
> - **id_new**: id of the new socket
> - **ref**: grant reference of the data ring interface (`struct
> pvcalls_data_intf`)
> - **evtchn**: port number of the evtchn to signal activity on the data ring
>
> Request binary layout:
>
> 8 12 16 20 24 28 32
> +-------+-------+-------+-------+-------+-------+
> | id | id_new | ref |evtchn |
> +-------+-------+-------+-------+-------+-------+
>
> Response additional fields:
>
> - **id**: id of the listening socket, echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +-------+-------+
> | id |
> +-------+-------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX accept function][accept] for error names; the corresponding
> error numbers are specified later in this document.
>
>
> #### Poll
>
> In this version of the protocol, the **poll** operation is only valid
> for passive sockets. For active sockets, the frontend should look at the
> state of the data ring. When a new connection is available in the queue
> of the passive socket, the backend generates a response and notifies the
> frontend.
>
> Request fields:
>
> - **cmd** value: 5
> - additional fields:
> - **id**: identifies the listening socket
>
> Request binary layout:
>
> 8 12 16
> +-------+-------+
> | id |
> +-------+-------+
>
>
> Response additional fields:
>
> - **id**: echoed back from request
>
> Response binary layout:
>
> 16 20 24
> +--------+--------+
> | id |
> +--------+--------+
>
> Return value:
>
> - 0 on success
> - See the [POSIX poll function][poll] for error names; the corresponding
> error
> numbers are specified later in this document.
>
> #### Error numbers
>
> The numbers corresponding to the error names specified by POSIX are:
>
> [EPERM] -1
> [ENOENT] -2
> [ESRCH] -3
> [EINTR] -4
> [EIO] -5
> [ENXIO] -6
> [E2BIG] -7
> [ENOEXEC] -8
> [EBADF] -9
> [ECHILD] -10
> [EAGAIN] -11
> [EWOULDBLOCK] -11
> [ENOMEM] -12
> [EACCES] -13
> [EFAULT] -14
> [EBUSY] -16
> [EEXIST] -17
> [EXDEV] -18
> [ENODEV] -19
> [EISDIR] -21
> [EINVAL] -22
> [ENFILE] -23
> [EMFILE] -24
> [ENOSPC] -28
> [EROFS] -30
> [EMLINK] -31
> [EDOM] -33
> [ERANGE] -34
> [EDEADLK] -35
> [EDEADLOCK] -35
> [ENAMETOOLONG] -36
> [ENOLCK] -37
> [ENOTEMPTY] -39
> [ENOSYS] -38
> [ENODATA] -61
> [ETIME] -62
> [EBADMSG] -74
> [EOVERFLOW] -75
> [EILSEQ] -84
> [ERESTART] -85
> [ENOTSOCK] -88
> [EOPNOTSUPP] -95
> [EAFNOSUPPORT] -97
> [EADDRINUSE] -98
> [EADDRNOTAVAIL] -99
> [ENOBUFS] -105
> [EISCONN] -106
> [ENOTCONN] -107
> [ETIMEDOUT] -110
> [ENOTSUP] -524
>
> #### Socket families and address format
>
> The following definitions and explicit sizes, together with POSIX
> [sys/socket.h][address] and [netinet/in.h][in] define socket families and
> address format. Please be aware that only the **domain** `AF_INET`, **type**
> `SOCK_STREAM` and **protocol** `0` are supported by this version of the
> spec, others return ENOTSUP.
>
> #define AF_UNSPEC 0
> #define AF_UNIX 1 /* Unix domain sockets */
> #define AF_LOCAL 1 /* POSIX name for AF_UNIX */
> #define AF_INET 2 /* Internet IP Protocol */
> #define AF_INET6 10 /* IP version 6 */
>
> #define SOCK_STREAM 1
> #define SOCK_DGRAM 2
> #define SOCK_RAW 3
>
> /* generic address format */
> struct sockaddr {
> uint16_t sa_family_t;
> char sa_data[26];
> };
>
> struct in_addr {
> uint32_t s_addr;
> };
>
> /* AF_INET address format */
> struct sockaddr_in {
> uint16_t sa_family_t;
> uint16_t sin_port;
> struct in_addr sin_addr;
> char sin_zero[20];
> };
>
>
> ### Data ring
>
> Data rings are used for sending and receiving data over a connected socket.
> They
> are created upon a successful **accept** or **connect** command.
> The **sendmsg** and **recvmsg** calls are implemented by sending data and
> receiving data from data rings.
>
> A data ring is composed of two pieces: the interface and the **in** and
> **out**
> buffers. The interface, represented by `struct pvcalls_ring_intf` is shared
> first and resides on the page whose grant reference is passed by **accept**
> and
> **connect** as parameter. `struct pvcalls_ring_intf` contains the list of
> grant
> references which constitute the **in** and **out** data buffers.
>
> #### Data ring interface
>
> struct pvcalls_data_intf {
> PVCALLS_RING_IDX in_cons, in_prod;
> int32_t in_error;
>
> uint8_t pad[52];
>
> PVCALLS_RING_IDX out_cons, out_prod;
> int32_t out_error;
>
> uint32_t ring_order;
> grant_ref_t ref[];
> };
>
> /* not actually C compliant (ring_order changes from socket to socket) */
> struct pvcalls_data {
> char in[((1<<ring_order)<<PAGE_SHIFT)/2];
> char out[((1<<ring_order)<<PAGE_SHIFT)/2];
> };
>
> - **ring_order**
> It represents the order of the data ring. The following list of grant
> references is of `(1 << ring_order)` elements. It cannot be greater than
> **max-dataring-page-order**, as specified by the backend on XenBus.
> - **ref[]**
> The list of grant references which will contain the actual data. They are
> mapped contiguosly in virtual memory. The first half of the pages is the
> **in** array, the second half is the **out** array. The array must
> have a power of two number of elements.
> - **in** is an array used as circular buffer
> It contains data read from the socket. The producer is the backend, the
> consumer is the frontend.
> - **out** is an array used as circular buffer
> It contains data to be written to the socket. The producer is the frontend,
> the consumer is the backend.
> - **in_cons** and **in_prod**
> Consumer and producer indices for data read from the socket. They keep track
> of how much data has already been consumed by the frontend from the **in**
> array. **in_prod** is increased by the backend, after writing data to
> **in**.
> **in_cons** is increased by the frontend, after reading data from **in**.
> - **out_cons**, **out_prod**
> Consumer and producer indices for the data to be written to the socket. They
> keep track of how much data has been written by the frontend to **out** and
> how much data has already been consumed by the backend. **out_prod** is
> increased by the frontend, after writing data to **out**. **out_cons** is
> increased by the backend, after reading data from **out**.
> - **in_error** and **out_error** They signal errors when reading from the
> socket
> (**in_error**) or when writing to the socket (**out_error**). 0 means no
> errors. When an error occurs, no further reads or writes operations are
> performed on the socket. In the case of an orderly socket shutdown (i.e.
> read
> returns 0) **in_error** is set to ENOTCONN. **in_error** and **out_error**
> are never set to EAGAIN or EWOULDBLOCK.
>
> The binary layout of `struct pvcalls_data_intf` follows:
>
> 0 4 8 12 64 68 72
> 76
> +---------+---------+---------+-----//-----+---------+---------+---------+
> | in_cons | in_prod |in_error | padding |out_cons |out_prod |out_error|
> +---------+---------+---------+-----//-----+---------+---------+---------+
>
> 76 80 84 88 4092 4096
> +---------+---------+---------+----//---+---------+
> |ring_orde| ref[0] | ref[1] | | ref[N] |
> +---------+---------+---------+----//---+---------+
>
> **N.B** For one page, N is maximum 1004 ((4096-80)/4), but given that N needs
> to be a power of two, actually max N is 512.
> The binary layout of the ring buffers follow:
>
> 0 ((1<<ring_order)<<PAGE_SHIFT)/2
> ((1<<ring_order)<<PAGE_SHIFT)
> +------------//-------------+------------//-------------+
> | in | out |
> +------------//-------------+------------//-------------+
>
> #### Workflow
>
> The **in** and **out** arrays are used as circular buffers:
>
> 0 sizeof(array) ==
> ((1<<ring_order)<<PAGE_SHIFT)/2
> +-----------------------------------+
> |to consume| free |to consume |
> +-----------------------------------+
> ^ ^
> prod cons
>
> 0 sizeof(array)
> +-----------------------------------+
> | free | to consume | free |
> +-----------------------------------+
> ^ ^
> cons prod
>
> The following function is provided to calculate how many bytes are currently
> left unconsumed in an array:
>
> #define _MASK_PVCALLS_IDX(idx, ring_size) ((idx) & (ring_size-1))
>
> static inline PVCALLS_RING_IDX pvcalls_ring_unconsumed(PVCALLS_RING_IDX
> prod,
> PVCALLS_RING_IDX cons,
> PVCALLS_RING_IDX ring_size)
> {
> PVCALLS_RING_IDX size;
>
> if (prod == cons)
> return 0;
>
> prod = _MASK_PVCALLS_IDX(prod, ring_size);
> cons = _MASK_PVCALLS_IDX(cons, ring_size);
>
> if (prod == cons)
> return ring_size;
>
> if (prod > cons)
> size = prod - cons;
> else {
> size = ring_size - cons;
> size += prod;
> }
> return size;
> }
>
> The producer (the backend for **in**, the frontend for **out**) writes to the
> array in the following way:
>
> - read *cons*, *prod*, *error* from shared memory
> - memory barrier
> - return on *error*
> - write to array at position *prod* up to *cons*, wrapping around the circular
> buffer when necessary
> - memory barrier
> - increase *prod*
> - notify the other end via evtchn
>
> The consumer (the backend for **out**, the frontend for **in**) reads from the
> array in the following way:
>
> - read *prod*, *cons*, *error* from shared memory
> - memory barrier
> - return on *error*
> - read from array at position *cons* up to *prod*, wrapping around the
> circular
> buffer when necessary
> - memory barrier
> - increase *cons*
> - notify the other end via evtchn
>
> The producer takes care of writing only as many bytes as available in the
> buffer
> up to *cons*. The consumer takes care of reading only as many bytes as
> available
> in the buffer up to *prod*. *error* is set by the backend when an error occurs
> writing or reading from the socket.
>
>
> [xenstore]: http://xenbits.xen.org/docs/unstable/misc/xenstore.txt
> [XenbusStateInitialising]:
> http://xenbits.xen.org/docs/unstable/hypercall/x86_64/include,public,io,xenbus.h.html
> [address]: http://pubs.opengroup.org/onlinepubs/7908799/xns/syssocket.h.html
> [in]:
> http://pubs.opengroup.org/onlinepubs/000095399/basedefs/netinet/in.h.html
> [socket]: http://pubs.opengroup.org/onlinepubs/009695399/functions/socket.html
> [connect]: http://pubs.opengroup.org/onlinepubs/7908799/xns/connect.html
> [shutdown]: http://pubs.opengroup.org/onlinepubs/7908799/xns/shutdown.html
> [bind]: http://pubs.opengroup.org/onlinepubs/7908799/xns/bind.html
> [listen]: http://pubs.opengroup.org/onlinepubs/7908799/xns/listen.html
> [accept]: http://pubs.opengroup.org/onlinepubs/7908799/xns/accept.html
> [poll]: http://pubs.opengroup.org/onlinepubs/7908799/xsh/poll.htmlAttachment:
pahole-pvcalls-64.txt Attachment:
pahole-pvcalls-32.txt _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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