netdev - Re: [PATCH v4] vsock.7: add VMADDR_CID

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Message-ID: <b3289245-ba42-24d4-b96c-267d09b2e37a@gmail.com>
Date:   Sat, 14 Mar 2020 23:02:19 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Stefano Garzarella <sgarzare@...hat.com>
Cc:     mtk.manpages@...il.com, Jorgen Hansen <jhansen@...are.com>,
        netdev@...r.kernel.org, linux-man@...r.kernel.org,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Dexuan Cui <decui@...rosoft.com>
Subject: Re: [PATCH v4] vsock.7: add VMADDR_CID_LOCAL description

Hello Stefano,

On 2/18/20 4:54 PM, Stefano Garzarella wrote:
> Linux 5.6 added the new well-known VMADDR_CID_LOCAL for
> local communication.
> 
> This patch explains how to use it and remove the legacy
> VMADDR_CID_RESERVED no longer available.
> 
> Reviewed-by: Jorgen Hansen <jhansen@...are.com>
> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> ---
> v4:
>     * removed "The" in the "Local communication" section [Stefan]
> v3:
>     * rephrased "Previous versions" part [Jorgen]
> v2:
>     * rephrased "Local communication" description [Stefan]
>     * added a mention of previous versions that supported
>       loopback only in the guest [Stefan]

Thanks. Patch applied.

Cheers,

Michael


> ---
>  man7/vsock.7 | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/man7/vsock.7 b/man7/vsock.7
> index c5ffcf07d..fa2c6e17e 100644
> --- a/man7/vsock.7
> +++ b/man7/vsock.7
> @@ -127,8 +127,8 @@ There are several special addresses:
>  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_LOCAL
> +(1) is the well-known address for local communication (loopback);
>  .B VMADDR_CID_HOST
>  (2)
>  is the well-known address of the host.
> @@ -164,6 +164,15 @@ Consider using
>  .B VMADDR_CID_ANY
>  when binding instead of getting the local CID with
>  .BR IOCTL_VM_SOCKETS_GET_LOCAL_CID .
> +.SS Local communication
> +.B VMADDR_CID_LOCAL
> +(1) directs packets to the same host that generated them. This is useful
> +for testing applications on a single host and for debugging.
> +.PP
> +The local CID obtained with
> +.BR IOCTL_VM_SOCKETS_GET_LOCAL_CID
> +can be used for the same purpose, but it is preferable to use
> +.B VMADDR_CID_LOCAL .
>  .SH ERRORS
>  .TP
>  .B EACCES
> @@ -222,6 +231,11 @@ are valid.
>  Support for VMware (VMCI) has been available since Linux 3.9.
>  KVM (virtio) is supported since Linux 4.8.
>  Hyper-V is supported since Linux 4.14.
> +.PP
> +VMADDR_CID_LOCAL is supported since Linux 5.6.
> +Local communication in the guest and on the host is available since Linux 5.6.
> +Previous versions only supported local communication within a guest
> +(not on the host), and only with some transports (VMCI and virtio).
>  .SH SEE ALSO
>  .BR bind (2),
>  .BR connect (2),
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/