[PATCH v2] vsock.7: document VSOCK socket address family

[PATCH v2] vsock.7: document VSOCK socket address family

[Stefan Hajnoczi]

The AF_VSOCK address family has been available since Linux 3.9 without a
corresponding man page.

This patch adds vsock.7 and describes its use along the same lines as
existing ip.7, unix.7, and netlink.7 man pages.

CC: Jorgen Hansen <jhansen-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org>
CC: Dexuan Cui <decui-0li6OtcxBFHby3iVrkZq2A@public.gmane.org>
Signed-off-by: Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 man7/vsock.7 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 180 insertions(+)
 create mode 100644 man7/vsock.7

diff --git a/man7/vsock.7 b/man7/vsock.7
new file mode 100644
index 000000000..46dc561f5
--- /dev/null
+++ b/man7/vsock.7
@@ -0,0 +1,180 @@
+.TH VSOCK 7 2017-11-30 "Linux" "Linux Programmer's Manual"
+.SH NAME
+vsock \- Linux VSOCK address family
+.SH SYNOPSIS
+.B #include <sys/socket.h>
+.br
+.B #include <linux/vm_sockets.h>
+.PP
+.IB stream_socket " = socket(AF_VSOCK, SOCK_STREAM, 0);"
+.br
+.IB datagram_socket " = socket(AF_VSOCK, SOCK_DGRAM, 0);"
+.SH DESCRIPTION
+The VSOCK address family facilitates communication between virtual machines and
+the host they are running on.  This address family is used by guest agents and
+hypervisor services that need a communications channel that is independent of
+virtual machine network configuration.
+.PP
+Valid socket types are
+.B SOCK_STREAM
+and
+.BR SOCK_DGRAM .
+.B SOCK_STREAM
+provides connection-oriented byte streams with guaranteed, in-order delivery.
+.B SOCK_DGRAM
+provides a connectionless datagram packet service with best-effort delivery and
+best-effort ordering.  Availability of these socket types is dependent on the
+underlying hypervisor.
+.PP
+A new socket is created with
+.PP
+    socket(AF_VSOCK, socket_type, 0);
+.PP
+When a process wants to establish a connection it calls
+.BR connect (2)
+with a given destination socket address.  The socket is automatically bound to
+a free port if unbound.
+.PP
+A process can listen for incoming connections by first binding to a socket
+address using
+.BR bind (2)
+and then calling
+.BR listen (2).
+.PP
+Data is transferred using the usual
+.BR send (2)
+and
+.BR recv (2)
+family of socket system calls.
+.SS Address format
+A socket address is defined as a combination of a 32-bit Context Identifier
+(CID) and a 32-bit port number.  The CID identifies the source or destination,
+which is either a virtual machine or the host.  The port number differentiates
+between multiple services running on a single machine.
+.PP
+.in +4n
+.EX
+struct sockaddr_vm {
+    sa_family_t     svm_family;     /* address family: AF_VSOCK */
+    unsigned short  svm_reserved1;
+    unsigned int    svm_port;       /* port in native byte order */
+    unsigned int    svm_cid;        /* address in native byte order */
+};
+.EE
+.in
+.PP
+.I svm_family
+is always set to
+.BR AF_VSOCK .
+.I svm_reserved1
+is always set to 0.
+.I svm_port
+contains the port in native byte order.
+The port numbers below 1024 are called
+.IR "privileged ports" .
+Only a process with
+.B CAP_NET_BIND_SERVER
+capability may
+.BR bind (2)
+to these port numbers.
+.PP
+There are several special addresses:
+.B VMADDR_CID_ANY
+(-1U)
+means any address for binding;
+.B VMADDR_CID_HYPERVISOR
+(0) is reserved for services built into the hypervisor;
+.B VMADDR_CID_RESERVED
+(1) must not be used;
+.B VMADDR_CID_HOST
+(2)
+is the well-known address of the host.
+.PP
+The special constant
+.B VMADDR_PORT_ANY
+(-1U)
+means any port number for binding.
+.SS Live migration
+Sockets are affected by live migration of virtual machines.  Connected
+.B SOCK_STREAM
+sockets become disconnected when the virtual machine migrates to a new host.
+Applications must reconnect when this happens.
+.PP
+The local CID may change across live migration if the old CID is not available
+on the new host.  Bound sockets are automatically updated to the new CID.
+.SS Ioctls
+.TP
+.B IOCTL_VM_SOCKETS_GET_LOCAL_CID
+Get the CID of the local machine.  The argument is a pointer to an unsigned int.
+.IP
+.in +4n
+.EX
+.IB error " = ioctl(" socket ", " IOCTL_VM_SOCKETS_GET_LOCAL_CID ", " &cid ");"
+.EE
+.in
+.IP
+Consider using
+.B VMADDR_CID_ANY
+when binding instead of getting the local CID with
+.BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
+.SH ERRORS
+.TP
+.B EACCES
+Unable to bind to a privileged port without the
+.B CAP_NET_BIND_SERVICE
+capability.
+.TP
+.B EINVAL
+Invalid parameters.  This includes:
+attempting to bind a socket that is already bound, providing an invalid struct
+.BR sockaddr_vm ,
+and other input validation errors.
+.TP
+.B EOPNOTSUPP
+Operation not supported.  This includes:
+the
+.B MSG_OOB
+flag that is not implemented for
+.BR sendmsg (2)
+and
+.B MSG_PEEK
+for
+.BR recvmsg (2).
+.TP
+.B EADDRINUSE
+Unable to bind to a port that is already in use.
+.TP
+.B EADDRNOTAVAIL
+Unable to find a free port for binding or unable to bind to a non-local CID.
+.TP
+.B ENOTCONN
+Unable to perform operation on an unconnected socket.
+.TP
+.B ENOPROTOOPT
+Invalid socket option in
+.BR setsockopt (2)
+or
+.BR getsockopt (2).
+.TP
+.B EPROTONOSUPPORT
+Invalid socket protocol number.  Protocol should always be 0.
+.TP
+.B ESOCKTNOSUPPORT
+Unsupported socket type in
+.BR socket (2).
+Only
+.B SOCK_STREAM
+and
+.B SOCK_DGRAM
+are valid.
+.SH VERSIONS
+Support for VMware (VMCI) has been available since Linux 3.9.  KVM (virtio) is
+supported since Linux 4.8.  Hyper-V is supported since 4.14.
+.SH SEE ALSO
+.BR socket (2),
+.BR bind (2),
+.BR connect (2),
+.BR listen (2),
+.BR send (2),
+.BR recv (2),
+.BR capabilities (7)
-- 
2.14.3

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Re: [PATCH v2] vsock.7: document VSOCK socket address family

[Jorgen S. Hansen]

> On Dec 5, 2017, at 11:56 AM, Stefan Hajnoczi <stefanha@redhat.com> wrote:
> 
> The AF_VSOCK address family has been available since Linux 3.9 without a
> corresponding man page.
> 
> This patch adds vsock.7 and describes its use along the same lines as
> existing ip.7, unix.7, and netlink.7 man pages.
> 
> CC: Jorgen Hansen <jhansen@vmware.com>
> CC: Dexuan Cui <decui@microsoft.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> man7/vsock.7 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 180 insertions(+)
> create mode 100644 man7/vsock.7
> 
> diff --git a/man7/vsock.7 b/man7/vsock.7
> new file mode 100644
> index 000000000..46dc561f5
> --- /dev/null
> +++ b/man7/vsock.7
> @@ -0,0 +1,180 @@
> +.TH VSOCK 7 2017-11-30 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +vsock \- Linux VSOCK address family
> +.SH SYNOPSIS
> +.B #include <sys/socket.h>
> +.br
> +.B #include <linux/vm_sockets.h>
> +.PP
> +.IB stream_socket " = socket(AF_VSOCK, SOCK_STREAM, 0);"
> +.br
> +.IB datagram_socket " = socket(AF_VSOCK, SOCK_DGRAM, 0);"
> +.SH DESCRIPTION
> +The VSOCK address family facilitates communication between virtual machines and
> +the host they are running on.  This address family is used by guest agents and
> +hypervisor services that need a communications channel that is independent of
> +virtual machine network configuration.
> +.PP
> +Valid socket types are
> +.B SOCK_STREAM
> +and
> +.BR SOCK_DGRAM .
> +.B SOCK_STREAM
> +provides connection-oriented byte streams with guaranteed, in-order delivery.
> +.B SOCK_DGRAM
> +provides a connectionless datagram packet service with best-effort delivery and
> +best-effort ordering.  Availability of these socket types is dependent on the
> +underlying hypervisor.
> +.PP
> +A new socket is created with
> +.PP
> +    socket(AF_VSOCK, socket_type, 0);
> +.PP
> +When a process wants to establish a connection it calls
> +.BR connect (2)
> +with a given destination socket address.  The socket is automatically bound to
> +a free port if unbound.
> +.PP
> +A process can listen for incoming connections by first binding to a socket
> +address using
> +.BR bind (2)
> +and then calling
> +.BR listen (2).
> +.PP
> +Data is transferred using the usual
> +.BR send (2)
> +and
> +.BR recv (2)
> +family of socket system calls.
> +.SS Address format
> +A socket address is defined as a combination of a 32-bit Context Identifier
> +(CID) and a 32-bit port number.  The CID identifies the source or destination,
> +which is either a virtual machine or the host.  The port number differentiates
> +between multiple services running on a single machine.
> +.PP
> +.in +4n
> +.EX
> +struct sockaddr_vm {
> +    sa_family_t     svm_family;     /* address family: AF_VSOCK */
> +    unsigned short  svm_reserved1;
> +    unsigned int    svm_port;       /* port in native byte order */
> +    unsigned int    svm_cid;        /* address in native byte order */
> +};
> +.EE
> +.in
> +.PP
> +.I svm_family
> +is always set to
> +.BR AF_VSOCK .
> +.I svm_reserved1
> +is always set to 0.
> +.I svm_port
> +contains the port in native byte order.
> +The port numbers below 1024 are called
> +.IR "privileged ports" .
> +Only a process with
> +.B CAP_NET_BIND_SERVER
> +capability may
> +.BR bind (2)
> +to these port numbers.
> +.PP
> +There are several special addresses:
> +.B VMADDR_CID_ANY
> +(-1U)
> +means any address for binding;
> +.B VMADDR_CID_HYPERVISOR
> +(0) is reserved for services built into the hypervisor;
> +.B VMADDR_CID_RESERVED
> +(1) must not be used;
> +.B VMADDR_CID_HOST
> +(2)
> +is the well-known address of the host.
> +.PP
> +The special constant
> +.B VMADDR_PORT_ANY
> +(-1U)
> +means any port number for binding.
> +.SS Live migration
> +Sockets are affected by live migration of virtual machines.  Connected
> +.B SOCK_STREAM
> +sockets become disconnected when the virtual machine migrates to a new host.
> +Applications must reconnect when this happens.
> +.PP
> +The local CID may change across live migration if the old CID is not available
> +on the new host.  Bound sockets are automatically updated to the new CID.
> +.SS Ioctls
> +.TP
> +.B IOCTL_VM_SOCKETS_GET_LOCAL_CID
> +Get the CID of the local machine.  The argument is a pointer to an unsigned int.
> +.IP
> +.in +4n
> +.EX
> +.IB error " = ioctl(" socket ", " IOCTL_VM_SOCKETS_GET_LOCAL_CID ", " &cid ");"
> +.EE
> +.in
> +.IP
> +Consider using
> +.B VMADDR_CID_ANY
> +when binding instead of getting the local CID with
> +.BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Unable to bind to a privileged port without the
> +.B CAP_NET_BIND_SERVICE
> +capability.
> +.TP
> +.B EINVAL
> +Invalid parameters.  This includes:
> +attempting to bind a socket that is already bound, providing an invalid struct
> +.BR sockaddr_vm ,
> +and other input validation errors.
> +.TP
> +.B EOPNOTSUPP
> +Operation not supported.  This includes:
> +the
> +.B MSG_OOB
> +flag that is not implemented for
> +.BR sendmsg (2)
> +and
> +.B MSG_PEEK
> +for
> +.BR recvmsg (2).
> +.TP
> +.B EADDRINUSE
> +Unable to bind to a port that is already in use.
> +.TP
> +.B EADDRNOTAVAIL
> +Unable to find a free port for binding or unable to bind to a non-local CID.
> +.TP
> +.B ENOTCONN
> +Unable to perform operation on an unconnected socket.
> +.TP
> +.B ENOPROTOOPT
> +Invalid socket option in
> +.BR setsockopt (2)
> +or
> +.BR getsockopt (2).
> +.TP
> +.B EPROTONOSUPPORT
> +Invalid socket protocol number.  Protocol should always be 0.
> +.TP
> +.B ESOCKTNOSUPPORT
> +Unsupported socket type in
> +.BR socket (2).
> +Only
> +.B SOCK_STREAM
> +and
> +.B SOCK_DGRAM
> +are valid.
> +.SH VERSIONS
> +Support for VMware (VMCI) has been available since Linux 3.9.  KVM (virtio) is
> +supported since Linux 4.8.  Hyper-V is supported since 4.14.
> +.SH SEE ALSO
> +.BR socket (2),
> +.BR bind (2),
> +.BR connect (2),
> +.BR listen (2),
> +.BR send (2),
> +.BR recv (2),
> +.BR capabilities (7)
> -- 
> 2.14.3
> 

Looks great to me. Thanks for doing this. I don’t have anything to add.

Reviewed-by: Jorgen Hansen <jhansen@vmware.com>

Re: [PATCH v2] vsock.7: document VSOCK socket address family

[Michael Kerrisk (man-pages)]

Hello Stefan,

Thanks for this page!

I have applied your patch, and made a few tweaks, but
I have some minor questions. Please see below.

On 12/05/2017 11:56 AM, Stefan Hajnoczi wrote:
> The AF_VSOCK address family has been available since Linux 3.9 without a
> corresponding man page.
> 
> This patch adds vsock.7 and describes its use along the same lines as
> existing ip.7, unix.7, and netlink.7 man pages.
> 
> CC: Jorgen Hansen <jhansen-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org>
> CC: Dexuan Cui <decui-0li6OtcxBFHby3iVrkZq2A@public.gmane.org>
> Signed-off-by: Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  man7/vsock.7 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 180 insertions(+)
>  create mode 100644 man7/vsock.7
> 
> diff --git a/man7/vsock.7 b/man7/vsock.7
> new file mode 100644
> index 000000000..46dc561f5
> --- /dev/null
> +++ b/man7/vsock.7
> @@ -0,0 +1,180 @@
> +.TH VSOCK 7 2017-11-30 "Linux" "Linux Programmer's Manual"
> +.SH NAME
> +vsock \- Linux VSOCK address family
> +.SH SYNOPSIS
> +.B #include <sys/socket.h>
> +.br
> +.B #include <linux/vm_sockets.h>
> +.PP
> +.IB stream_socket " = socket(AF_VSOCK, SOCK_STREAM, 0);"
> +.br
> +.IB datagram_socket " = socket(AF_VSOCK, SOCK_DGRAM, 0);"
> +.SH DESCRIPTION
> +The VSOCK address family facilitates communication between virtual machines and
> +the host they are running on.  This address family is used by guest agents and
> +hypervisor services that need a communications channel that is independent of
> +virtual machine network configuration.
> +.PP
> +Valid socket types are
> +.B SOCK_STREAM
> +and
> +.BR SOCK_DGRAM .
> +.B SOCK_STREAM
> +provides connection-oriented byte streams with guaranteed, in-order delivery.
> +.B SOCK_DGRAM
> +provides a connectionless datagram packet service with best-effort delivery and
> +best-effort ordering.  Availability of these socket types is dependent on the
> +underlying hypervisor.
> +.PP
> +A new socket is created with
> +.PP
> +    socket(AF_VSOCK, socket_type, 0);
> +.PP
> +When a process wants to establish a connection it calls
> +.BR connect (2)
> +with a given destination socket address.  The socket is automatically bound to
> +a free port if unbound.
> +.PP
> +A process can listen for incoming connections by first binding to a socket
> +address using
> +.BR bind (2)
> +and then calling
> +.BR listen (2).
> +.PP
> +Data is transferred using the usual
> +.BR send (2)
> +and
> +.BR recv (2)

Or equally, write(2) and read(2), right? By failing to mention those, the
text subtly implies that send(2) and recv(2) are preferred, but I don't
suppose that is true.

> +family of socket system calls.
> +.SS Address format
> +A socket address is defined as a combination of a 32-bit Context Identifier
> +(CID) and a 32-bit port number.  The CID identifies the source or destination,
> +which is either a virtual machine or the host.  The port number differentiates
> +between multiple services running on a single machine.
> +.PP
> +.in +4n
> +.EX
> +struct sockaddr_vm {
> +    sa_family_t     svm_family;     /* address family: AF_VSOCK */
> +    unsigned short  svm_reserved1;
> +    unsigned int    svm_port;       /* port in native byte order */
> +    unsigned int    svm_cid;        /* address in native byte order */
> +};
> +.EE
> +.in
> +.PP
> +.I svm_family
> +is always set to
> +.BR AF_VSOCK .
> +.I svm_reserved1
> +is always set to 0.
> +.I svm_port
> +contains the port in native byte order.
> +The port numbers below 1024 are called
> +.IR "privileged ports" .
> +Only a process with
> +.B CAP_NET_BIND_SERVER
> +capability may
> +.BR bind (2)
> +to these port numbers.
> +.PP
> +There are several special addresses:
> +.B VMADDR_CID_ANY
> +(-1U)
> +means any address for binding;
> +.B VMADDR_CID_HYPERVISOR
> +(0) is reserved for services built into the hypervisor;
> +.B VMADDR_CID_RESERVED
> +(1) must not be used;
> +.B VMADDR_CID_HOST
> +(2)
> +is the well-known address of the host.
> +.PP
> +The special constant
> +.B VMADDR_PORT_ANY
> +(-1U)
> +means any port number for binding.
> +.SS Live migration
> +Sockets are affected by live migration of virtual machines.  Connected
> +.B SOCK_STREAM
> +sockets become disconnected when the virtual machine migrates to a new host.
> +Applications must reconnect when this happens.
> +.PP
> +The local CID may change across live migration if the old CID is not available
> +on the new host.  Bound sockets are automatically updated to the new CID.
> +.SS Ioctls
> +.TP
> +.B IOCTL_VM_SOCKETS_GET_LOCAL_CID
> +Get the CID of the local machine.  The argument is a pointer to an unsigned int.
> +.IP
> +.in +4n
> +.EX
> +.IB error " = ioctl(" socket ", " IOCTL_VM_SOCKETS_GET_LOCAL_CID ", " &cid ");"
> +.EE
> +.in
> +.IP
> +Consider using
> +.B VMADDR_CID_ANY
> +when binding instead of getting the local CID with
> +.BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
> +.SH ERRORS
> +.TP
> +.B EACCES
> +Unable to bind to a privileged port without the
> +.B CAP_NET_BIND_SERVICE
> +capability.
> +.TP
> +.B EINVAL
> +Invalid parameters.  This includes:
> +attempting to bind a socket that is already bound, providing an invalid struct
> +.BR sockaddr_vm ,
> +and other input validation errors.
> +.TP
> +.B EOPNOTSUPP
> +Operation not supported.  This includes:
> +the
> +.B MSG_OOB
> +flag that is not implemented for
> +.BR sendmsg (2)
> +and
> +.B MSG_PEEK
> +for
> +.BR recvmsg (2).

So these errors might also occur for send() and recv(), right?

> +.TP
> +.B EADDRINUSE
> +Unable to bind to a port that is already in use.
> +.TP
> +.B EADDRNOTAVAIL
> +Unable to find a free port for binding or unable to bind to a non-local CID.
> +.TP
> +.B ENOTCONN
> +Unable to perform operation on an unconnected socket.
> +.TP
> +.B ENOPROTOOPT
> +Invalid socket option in
> +.BR setsockopt (2)
> +or
> +.BR getsockopt (2).
> +.TP
> +.B EPROTONOSUPPORT
> +Invalid socket protocol number.  Protocol should always be 0.
> +.TP
> +.B ESOCKTNOSUPPORT
> +Unsupported socket type in
> +.BR socket (2).
> +Only
> +.B SOCK_STREAM
> +and
> +.B SOCK_DGRAM
> +are valid.
> +.SH VERSIONS
> +Support for VMware (VMCI) has been available since Linux 3.9.  KVM (virtio) is
> +supported since Linux 4.8.  Hyper-V is supported since 4.14.
> +.SH SEE ALSO
> +.BR socket (2),
> +.BR bind (2),
> +.BR connect (2),
> +.BR listen (2),
> +.BR send (2),
> +.BR recv (2),
> +.BR capabilities (7)

Cheers,

Michael


-- 
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Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH v2] vsock.7: document VSOCK socket address family

[Michael Kerrisk (man-pages)]

On 12/06/2017 03:06 PM, Jorgen S. Hansen wrote:
> 
>> On Dec 5, 2017, at 11:56 AM, Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>>
>> The AF_VSOCK address family has been available since Linux 3.9 without a
>> corresponding man page.
>>
>> This patch adds vsock.7 and describes its use along the same lines as
>> existing ip.7, unix.7, and netlink.7 man pages.
>>
>> CC: Jorgen Hansen <jhansen-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org>
>> CC: Dexuan Cui <decui-0li6OtcxBFHby3iVrkZq2A@public.gmane.org>
>> Signed-off-by: Stefan Hajnoczi <stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> ---
>> man7/vsock.7 | 180 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 180 insertions(+)
>> create mode 100644 man7/vsock.7
>>
>> diff --git a/man7/vsock.7 b/man7/vsock.7
>> new file mode 100644
>> index 000000000..46dc561f5
>> --- /dev/null
>> +++ b/man7/vsock.7
>> @@ -0,0 +1,180 @@
>> +.TH VSOCK 7 2017-11-30 "Linux" "Linux Programmer's Manual"
>> +.SH NAME
>> +vsock \- Linux VSOCK address family
>> +.SH SYNOPSIS
>> +.B #include <sys/socket.h>
>> +.br
>> +.B #include <linux/vm_sockets.h>
>> +.PP
>> +.IB stream_socket " = socket(AF_VSOCK, SOCK_STREAM, 0);"
>> +.br
>> +.IB datagram_socket " = socket(AF_VSOCK, SOCK_DGRAM, 0);"
>> +.SH DESCRIPTION
>> +The VSOCK address family facilitates communication between virtual machines and
>> +the host they are running on.  This address family is used by guest agents and
>> +hypervisor services that need a communications channel that is independent of
>> +virtual machine network configuration.
>> +.PP
>> +Valid socket types are
>> +.B SOCK_STREAM
>> +and
>> +.BR SOCK_DGRAM .
>> +.B SOCK_STREAM
>> +provides connection-oriented byte streams with guaranteed, in-order delivery.
>> +.B SOCK_DGRAM
>> +provides a connectionless datagram packet service with best-effort delivery and
>> +best-effort ordering.  Availability of these socket types is dependent on the
>> +underlying hypervisor.
>> +.PP
>> +A new socket is created with
>> +.PP
>> +    socket(AF_VSOCK, socket_type, 0);
>> +.PP
>> +When a process wants to establish a connection it calls
>> +.BR connect (2)
>> +with a given destination socket address.  The socket is automatically bound to
>> +a free port if unbound.
>> +.PP
>> +A process can listen for incoming connections by first binding to a socket
>> +address using
>> +.BR bind (2)
>> +and then calling
>> +.BR listen (2).
>> +.PP
>> +Data is transferred using the usual
>> +.BR send (2)
>> +and
>> +.BR recv (2)
>> +family of socket system calls.
>> +.SS Address format
>> +A socket address is defined as a combination of a 32-bit Context Identifier
>> +(CID) and a 32-bit port number.  The CID identifies the source or destination,
>> +which is either a virtual machine or the host.  The port number differentiates
>> +between multiple services running on a single machine.
>> +.PP
>> +.in +4n
>> +.EX
>> +struct sockaddr_vm {
>> +    sa_family_t     svm_family;     /* address family: AF_VSOCK */
>> +    unsigned short  svm_reserved1;
>> +    unsigned int    svm_port;       /* port in native byte order */
>> +    unsigned int    svm_cid;        /* address in native byte order */
>> +};
>> +.EE
>> +.in
>> +.PP
>> +.I svm_family
>> +is always set to
>> +.BR AF_VSOCK .
>> +.I svm_reserved1
>> +is always set to 0.
>> +.I svm_port
>> +contains the port in native byte order.
>> +The port numbers below 1024 are called
>> +.IR "privileged ports" .
>> +Only a process with
>> +.B CAP_NET_BIND_SERVER
>> +capability may
>> +.BR bind (2)
>> +to these port numbers.
>> +.PP
>> +There are several special addresses:
>> +.B VMADDR_CID_ANY
>> +(-1U)
>> +means any address for binding;
>> +.B VMADDR_CID_HYPERVISOR
>> +(0) is reserved for services built into the hypervisor;
>> +.B VMADDR_CID_RESERVED
>> +(1) must not be used;
>> +.B VMADDR_CID_HOST
>> +(2)
>> +is the well-known address of the host.
>> +.PP
>> +The special constant
>> +.B VMADDR_PORT_ANY
>> +(-1U)
>> +means any port number for binding.
>> +.SS Live migration
>> +Sockets are affected by live migration of virtual machines.  Connected
>> +.B SOCK_STREAM
>> +sockets become disconnected when the virtual machine migrates to a new host.
>> +Applications must reconnect when this happens.
>> +.PP
>> +The local CID may change across live migration if the old CID is not available
>> +on the new host.  Bound sockets are automatically updated to the new CID.
>> +.SS Ioctls
>> +.TP
>> +.B IOCTL_VM_SOCKETS_GET_LOCAL_CID
>> +Get the CID of the local machine.  The argument is a pointer to an unsigned int.
>> +.IP
>> +.in +4n
>> +.EX
>> +.IB error " = ioctl(" socket ", " IOCTL_VM_SOCKETS_GET_LOCAL_CID ", " &cid ");"
>> +.EE
>> +.in
>> +.IP
>> +Consider using
>> +.B VMADDR_CID_ANY
>> +when binding instead of getting the local CID with
>> +.BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
>> +.SH ERRORS
>> +.TP
>> +.B EACCES
>> +Unable to bind to a privileged port without the
>> +.B CAP_NET_BIND_SERVICE
>> +capability.
>> +.TP
>> +.B EINVAL
>> +Invalid parameters.  This includes:
>> +attempting to bind a socket that is already bound, providing an invalid struct
>> +.BR sockaddr_vm ,
>> +and other input validation errors.
>> +.TP
>> +.B EOPNOTSUPP
>> +Operation not supported.  This includes:
>> +the
>> +.B MSG_OOB
>> +flag that is not implemented for
>> +.BR sendmsg (2)
>> +and
>> +.B MSG_PEEK
>> +for
>> +.BR recvmsg (2).
>> +.TP
>> +.B EADDRINUSE
>> +Unable to bind to a port that is already in use.
>> +.TP
>> +.B EADDRNOTAVAIL
>> +Unable to find a free port for binding or unable to bind to a non-local CID.
>> +.TP
>> +.B ENOTCONN
>> +Unable to perform operation on an unconnected socket.
>> +.TP
>> +.B ENOPROTOOPT
>> +Invalid socket option in
>> +.BR setsockopt (2)
>> +or
>> +.BR getsockopt (2).
>> +.TP
>> +.B EPROTONOSUPPORT
>> +Invalid socket protocol number.  Protocol should always be 0.
>> +.TP
>> +.B ESOCKTNOSUPPORT
>> +Unsupported socket type in
>> +.BR socket (2).
>> +Only
>> +.B SOCK_STREAM
>> +and
>> +.B SOCK_DGRAM
>> +are valid.
>> +.SH VERSIONS
>> +Support for VMware (VMCI) has been available since Linux 3.9.  KVM (virtio) is
>> +supported since Linux 4.8.  Hyper-V is supported since 4.14.
>> +.SH SEE ALSO
>> +.BR socket (2),
>> +.BR bind (2),
>> +.BR connect (2),
>> +.BR listen (2),
>> +.BR send (2),
>> +.BR recv (2),
>> +.BR capabilities (7)
>> -- 
>> 2.14.3
>>
> 
> Looks great to me. Thanks for doing this. I don’t have anything to add.
> 
> Reviewed-by: Jorgen Hansen <jhansen-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org>

Thanks, Jorgen!

Cheers,

Michael


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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Re: [PATCH v2] vsock.7: document VSOCK socket address family

[Stefan Hajnoczi]

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On Mon, Dec 11, 2017 at 08:32:20PM +0100, Michael Kerrisk (man-pages) wrote:
> On 12/05/2017 11:56 AM, Stefan Hajnoczi wrote:
> > +Data is transferred using the usual
> > +.BR send (2)
> > +and
> > +.BR recv (2)
> 
> Or equally, write(2) and read(2), right? By failing to mention those, the
> text subtly implies that send(2) and recv(2) are preferred, but I don't
> suppose that is true.
> 
> > +family of socket system calls.

Yes, this file descriptor is a socket so write(2) and read(2) work.

I said "family of socket system calls" to avoid listing all the
variations of send(2), sendmsg(2), sendfile(2), sendmmsg(2), etc but I
guess that doesn't include the read(2)/write(2) family of syscalls
(readv(2)/writev(2)).

Will send a follow-up patch to clarify this.

> > +.B EOPNOTSUPP
> > +Operation not supported.  This includes:
> > +the
> > +.B MSG_OOB
> > +flag that is not implemented for
> > +.BR sendmsg (2)
> > +and
> > +.B MSG_PEEK
> > +for
> > +.BR recvmsg (2).
> 
> So these errors might also occur for send() and recv(), right?

Yes, I'll change this to "the send(2) family of syscalls" and "recv(2)
family of syscalls", respectively.

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