Features/VirtioSerial

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== Summary ==
 
== Summary ==
<!-- A sentence or two summarizing what this feature is and what it will do.  This information is used for the overall feature summary page for each release. -->
 
 
This feature adds a virtio-serial device to guests running on top of qemu and kvm. It exposes multiple ports to the guest in the form of simple char devices for simple IO between the guest and host userspaces.
 
This feature adds a virtio-serial device to guests running on top of qemu and kvm. It exposes multiple ports to the guest in the form of simple char devices for simple IO between the guest and host userspaces.
  
 
== Owner ==
 
== Owner ==
<!--This should link to your home wiki page so we know who you are-->
 
 
* Name: [[User:Amitshah| Amit Shah]]
 
* Name: [[User:Amitshah| Amit Shah]]
 
<!-- Include you email address that you can be reached should people want to contact you about helping with your feature, status is requested, or  technical issues need to be resolved-->
 
 
* email: amit.shah@redhat.com
 
* email: amit.shah@redhat.com
  
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== Detailed Description ==
 
== Detailed Description ==
<!-- Expand on the summary, if appropriate.  A couple sentences suffices to explain the goal, but the more details you can provide the better. -->
 
 
Also known as 'vmchannel', a transport mechanism is needed for communication between the host userspace and guest userspace for achieving things like making clipboard copy/paste work seamlessly across the host and guest, locking the guest screen in case the vnc session to the guest is closed and so on. This can be used in offline cases as well, for example with libguestfs to probe which file systems the guest uses, the apps installed, etc.
 
Also known as 'vmchannel', a transport mechanism is needed for communication between the host userspace and guest userspace for achieving things like making clipboard copy/paste work seamlessly across the host and guest, locking the guest screen in case the vnc session to the guest is closed and so on. This can be used in offline cases as well, for example with libguestfs to probe which file systems the guest uses, the apps installed, etc.
  
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== Benefit to Fedora ==
 
== Benefit to Fedora ==
<!-- What is the benefit to the platform?  If this is a major capability update, what has changed?  If this is a new feature, what capabilities does it bring? Why will Fedora become a better distribution or project because of this feature?-->
 
 
Some benefits include:
 
Some benefits include:
 
* a communication channel between the guest and the host even when guest networking is disabled
 
* a communication channel between the guest and the host even when guest networking is disabled
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== Scope ==
 
== Scope ==
<!-- What work do the developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 
 
Changes are required in QEMU and Linux. A few udev rules will have to be added to dynamically create ports for the device.
 
Changes are required in QEMU and Linux. A few udev rules will have to be added to dynamically create ports for the device.
  
 
== How To Test ==
 
== How To Test ==
<!-- This does not need to be a full-fledged document.  Describe the dimensions of tests that this feature is expected to pass when it is done.  If it needs to be tested with different hardware or software configurations, indicate them.  The more specific you can be, the better the community testing can be.
 
 
Remember that you are writing this how to for interested testers to use to check out your feature - documenting what you do for testing is OK, but it's much better to document what *I* can do to test your feature.
 
 
A good "how to test" should answer these four questions:
 
 
0. What special hardware / data / etc. is needed (if any)?
 
1. How do I prepare my system to test this feature? What packages
 
need to be installed, config files edited, etc.?
 
2. What specific actions do I perform to check that the feature is
 
working like it's supposed to?
 
3. What are the expected results of those actions?
 
-->
 
 
When starting qemu or kvm guests from the command line, a new option, -virtioserial unix:/path/to/socket will create a PCI device and expose one serial port to the guest. The guest kernel should load the virtio-serial.ko module and expose a /dev/vmch0 port to guest userspace app developers. Data written into host's /path/to/socket will then be relayed to the guest and a guest app should be able to read the data from /dev/vmch0.
 
When starting qemu or kvm guests from the command line, a new option, -virtioserial unix:/path/to/socket will create a PCI device and expose one serial port to the guest. The guest kernel should load the virtio-serial.ko module and expose a /dev/vmch0 port to guest userspace app developers. Data written into host's /path/to/socket will then be relayed to the guest and a guest app should be able to read the data from /dev/vmch0.
  
 
== User Experience ==
 
== User Experience ==
<!-- If this feature is noticeable by its target audience, how will their experiences change as a result?  Describe what they will see or notice. -->
 
 
Virtio-serial is just the transport and by itself won't be user-visible. Applications written on top of virtio-serial to communicate data between the host and guest OSes will bring user-visible changes.
 
Virtio-serial is just the transport and by itself won't be user-visible. Applications written on top of virtio-serial to communicate data between the host and guest OSes will bring user-visible changes.
  
 
== Dependencies ==
 
== Dependencies ==
<!-- What other packages (RPMs) depend on this package?  Are there changes outside the developers' control on which completion of this feature depends?  In other words, completion of another feature owned by someone else and might cause you to not be able to finish on time or that you would need to coordinate?  Other upstream projects like the kernel (if this is not a kernel feature)? -->
 
 
This feature depends on acceptance of the patches by the QEMU and Linux kernel communities.
 
This feature depends on acceptance of the patches by the QEMU and Linux kernel communities.
  
 
== Contingency Plan ==
 
== Contingency Plan ==
<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "None necessary, revert to previous release behaviour."  Or it might not.  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
 
 
QEMU currently contains an alternative implementation of vmchannel using userland networking which is slower but similar in feature set. Continue using that interface in case virtio-serial is not ready.
 
QEMU currently contains an alternative implementation of vmchannel using userland networking which is slower but similar in feature set. Continue using that interface in case virtio-serial is not ready.
  
 
== Documentation ==
 
== Documentation ==
<!-- Is there upstream documentation on this feature, or notes you have written yourself?  Link to that material here so other interested developers can get involved. -->
 
 
http://www.linux-kvm.org/page/VMchannel_Requirements
 
http://www.linux-kvm.org/page/VMchannel_Requirements
  
 
== Release Notes ==
 
== Release Notes ==
<!-- The Fedora Release Notes inform end-users about what is new in the release.  Examples of past release notes are here: http://docs.fedoraproject.org/release-notes/ -->
 
<!-- The release notes also help users know how to deal with platform changes such as ABIs/APIs, configuration or data file formats, or upgrade concerns.  If there are any such changes involved in this feature, indicate them here.  You can also link to upstream documentation if it satisfies this need.  This information forms the basis of the release notes edited by the documentation team and shipped with the release. -->
 
 
* New virtio-serial pci device exposed to guests running on top of qemu and kvm. A single device exposes multiple serial ports for simple guest <-> host communication.
 
* New virtio-serial pci device exposed to guests running on top of qemu and kvm. A single device exposes multiple serial ports for simple guest <-> host communication.
  
 
== Comments and Discussion ==
 
== Comments and Discussion ==
* See [[Talk:VirtioSerial]] <!-- This adds a link to the "discussion" tab associated with your page.  This provides the ability to have ongoing comments or conversation without bogging down the main feature page -->
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* See [[Talk:VirtioSerial]]
  
 
[[Category:FeatureReadyForFesco]]
 
[[Category:FeatureReadyForFesco]]
<!-- When your feature page is completed and ready for review -->
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[[Category:Virtualization|VirtioSerial]]
<!-- remove Category:FeaturePageIncomplete and change it to Category:FeatureReadyForWrangler -->
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[[Category:F12_Virt_Features|VirtioSerial]]
<!-- After review, the feature wrangler will move your page to Category:FeatureReadyForFesco... if it still needs more work it will move back to Category:FeaturePageIncomplete-->
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<!-- A pretty picture of the page category usage is at: https://fedoraproject.org/wiki/Features/Policy/Process -->
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<!-- Note that the current Feature guidelines require useful Scope and Test Plans at certain milestones; QA is responsible for checking these, and will change this category as needed. -->
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Revision as of 08:00, 10 July 2009

Contents

Virtio-Serial

Summary

This feature adds a virtio-serial device to guests running on top of qemu and kvm. It exposes multiple ports to the guest in the form of simple char devices for simple IO between the guest and host userspaces.

Owner

Current status

  • Targeted release: Fedora 12
  • Last updated: 2009-06-29
  • Percentage of completion: 60%

Detailed Description

Also known as 'vmchannel', a transport mechanism is needed for communication between the host userspace and guest userspace for achieving things like making clipboard copy/paste work seamlessly across the host and guest, locking the guest screen in case the vnc session to the guest is closed and so on. This can be used in offline cases as well, for example with libguestfs to probe which file systems the guest uses, the apps installed, etc.

Virtio-serial is just the transport protocol that will enable such applications to be written. It has two parts: (a) device emulation in qemu that presents a virtio-pci device to the guest and (b) a guest driver that presents a char device interface to userspace applications.

Benefit to Fedora

Some benefits include:

  • a communication channel between the guest and the host even when guest networking is disabled
  • applications can be written on top of the transport to achieve better guest-host cooperation, eg., clipboard copy/paste support between the host and the guest
  • libguestfs currently uses a low-performing vmchannel interface. Updating libguestfs to use this interface will achieve better speeds.

Scope

Changes are required in QEMU and Linux. A few udev rules will have to be added to dynamically create ports for the device.

How To Test

When starting qemu or kvm guests from the command line, a new option, -virtioserial unix:/path/to/socket will create a PCI device and expose one serial port to the guest. The guest kernel should load the virtio-serial.ko module and expose a /dev/vmch0 port to guest userspace app developers. Data written into host's /path/to/socket will then be relayed to the guest and a guest app should be able to read the data from /dev/vmch0.

User Experience

Virtio-serial is just the transport and by itself won't be user-visible. Applications written on top of virtio-serial to communicate data between the host and guest OSes will bring user-visible changes.

Dependencies

This feature depends on acceptance of the patches by the QEMU and Linux kernel communities.

Contingency Plan

QEMU currently contains an alternative implementation of vmchannel using userland networking which is slower but similar in feature set. Continue using that interface in case virtio-serial is not ready.

Documentation

http://www.linux-kvm.org/page/VMchannel_Requirements

Release Notes

  • New virtio-serial pci device exposed to guests running on top of qemu and kvm. A single device exposes multiple serial ports for simple guest <-> host communication.

Comments and Discussion