Commit 026c69db authored by Dariusz Stojaczyk's avatar Dariusz Stojaczyk Committed by Jim Harris
Browse files

doc/vhost_processing: replace the ASCII diagram with an SVG one 



All credits go to Tomasz.

Change-Id: I0664aad9abb87f9d04c243654f308c22f968cef2
Signed-off-by: default avatarTomasz Kulasek <tomaszx.kulasek@intel.com>
Signed-off-by: default avatarDariusz Stojaczyk <dariuszx.stojaczyk@intel.com>
Reviewed-on: https://review.gerrithub.io/412119


Reviewed-by: default avatarDaniel Verkamp <daniel.verkamp@intel.com>
Reviewed-by: default avatarJim Harris <james.r.harris@intel.com>
Reviewed-by: default avatarBen Walker <benjamin.walker@intel.com>
Tested-by: default avatarSPDK Automated Test System <sys_sgsw@intel.com>
parent 8a989c7c

doc/Doxyfile

+1 −1
Original line number Diff line number Diff line
@@ -907,7 +907,7 @@ EXAMPLE_RECURSIVE = NO 
# that contain images that are to be included in the documentation (see the

# \image command).



IMAGE_PATH             =

IMAGE_PATH             = img



# The INPUT_FILTER tag can be used to specify a program that doxygen should

# invoke to filter for each input file. Doxygen will invoke the filter program

doc/img/qemu_vhost_data_flow.svg

0 → 100644
+2 −0
Original line number Diff line number Diff line 
<?xml version="1.0" encoding="UTF-8"?>

<svg version="1.1" viewBox="0 0 187.85 104.34" xmlns="http://www.w3.org/2000/svg" xmlns:cc="http://creativecommons.org/ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"><defs><marker id="a" style="overflow:visible" orient="auto"><path transform="matrix(1.1,0,0,1.1,1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="b" style="overflow:visible" orient="auto"><path transform="matrix(-1.1,0,0,-1.1,-1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="j" style="overflow:visible" orient="auto"><path transform="matrix(1.1,0,0,1.1,1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="l" style="overflow:visible" orient="auto"><path transform="matrix(1.1,0,0,1.1,1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="c" style="overflow:visible" orient="auto"><path transform="matrix(-1.1,0,0,-1.1,-1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="d" style="overflow:visible" orient="auto"><path transform="matrix(-1.1,0,0,-1.1,-1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker 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4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="i" style="overflow:visible" orient="auto"><path transform="matrix(-1.1,0,0,-1.1,-1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker><marker id="k" style="overflow:visible" orient="auto"><path transform="matrix(-1.1,0,0,-1.1,-1.1,0)" d="m8.7186 4.0337-10.926-4.0177 10.926-4.0177c-1.7455 2.3721-1.7354 5.6175-6e-7 8.0354z" style="fill-rule:evenodd;fill:#000000;stroke-linejoin:round;stroke-width:.625;stroke:#000000"/></marker></defs><metadata><rdf:RDF><cc:Work rdf:about=""><dc:format>image/svg+xml</dc:format><dc:type rdf:resource="http://purl.org/dc/dcmitype/StillImage"/><dc:title/><dc:creator><cc:Agent><dc:title>Tomasz Kulasek</dc:title></cc:Agent></dc:creator></cc:Work></rdf:RDF></metadata><g transform="translate(2.5133 -10.794)"><rect x="-2.5133" y="10.794" width="187.85" height="104.34" style="fill:#fffffe"/></g><g transform="translate(-2.6458 -133.04)"><rect x="10.583" y="135.6" width="79.375" height="74.083" ry="2.6458" style="fill:#d5e5ff;stroke-width:.5;stroke:#000000"/><rect x="63.5" y="199.1" width="21.167" height="5.2917" style="fill:none;stroke-dasharray:1.05833327, 1.05833327;stroke-width:.26458;stroke:#000000"/><rect x="21.167" y="152.8" width="58.208" height="30.427" ry="2.6458" style="fill:none;stroke-width:.26458;stroke:#000000"/><path d="m26.458 191.17v-7.9375" style="fill:none;marker-end:url(#h);stroke-dasharray:1.05999995, 1.05999995;stroke-width:.265;stroke:#000000"/><path d="m34.396 183.23v7.9375" style="fill:none;marker-end:url(#i);stroke-dasharray:1.05999995, 1.05999995;stroke-width:.265;stroke:#000000"/><rect x="63.5" y="218.95" width="15.875" height="15.875" ry="2.6458" style="fill:#ffd5e5;stroke-width:.5;stroke:#000000"/><path d="m71.438 204.4v14.552" style="fill:none;marker-end:url(#g);stroke-dasharray:1.5874999, 1.5874999;stroke-width:.26458;stroke:#000000"/><rect x="15.875" y="143.54" width="68.792" height="39.687" ry="2.6458" style="fill:none;stroke-width:.26458;stroke:#000000"/><path d="m63.5 226.89h-58.208l-1e-7-62.177 10.583-1e-5" style="fill:none;marker-end:url(#f);stroke-dasharray:1.58999992, 1.58999992;stroke-width:.265;stroke:#000000"/><g transform="translate(-.13251 -.1325)"><rect x="90.091" y="135.74" width="97.896" height="52.917" ry="2.6458" style="fill:#fff6d5;stroke-width:.5;stroke:#000000"/><g><g transform="translate(-10.451 .1325)"><rect x="132.29" y="152.8" width="60.854" height="31.75" ry="2.6458" style="fill:none;stroke-width:.265;stroke:#000000"/><text x="150.91241" y="158.04379" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;text-align:center;text-anchor:middle;word-spacing:0px" xml:space="preserve"><tspan x="150.91241" y="158.04379">Vhost-SCSI device</tspan></text></g><g transform="translate(-10.451 -2.5133)"><rect x="137.58" y="164.71" width="50.271" height="15.875" ry="2.6458" style="fill:none;stroke-opacity:.99034;stroke-width:.265;stroke:#000000"/><text x="139.99663" y="171.41422" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="139.99663" y="171.41422" style="font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal">SPDK bdev(s)</tspan><tspan x="139.99663" y="175.82394" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal">(NVMe, NVMf, Ceph RBD, PMEM)</tspan></text></g></g></g><text x="92.37162" y="140.93028" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="92.37162" y="140.93028" style="font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">SPDK vhost</tspan></text><text x="13.482382" y="140.44109" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="13.482382" y="140.44109" style="font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">QEMU</tspan></text><g transform="translate(2.5609e-6 -5.2917)"><rect x="15.875" y="196.46" width="29.104" height="13.229" style="fill:none;stroke-width:.26458;stroke:#000000"/><text x="16.636366" y="201.47922" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="16.636366" y="201.47922" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Virtio-SCSI device</tspan></text></g><g transform="translate(-5.0685e-6 -5.2917)"><rect x="44.979" y="196.46" width="39.688" height="13.229" ry="0" style="fill:none;stroke-width:.26458;stroke:#000000"/><text x="46.195286" y="201.31316" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="46.195286" y="201.31316" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Vhost-user driver (master)</tspan></text></g><g transform="translate(0 6.6146)"><g><rect x="54.24" y="154.12" width="55.562" height="17.198" ry="2.6458" style="fill:#e3f4d7;stroke-dasharray:0.52999997, 0.52999997;stroke-width:.265;stroke:#000000"/><text x="64.25103" y="157.5067" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="64.25103" y="157.5067" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Shared hugepage memory</tspan></text></g><g><g><rect x="58.208" y="159.42" width="47.625" height="5.2917" ry="5.0849e-6" style="fill:#c3e8aa;stroke-width:.265;stroke:#000000"/><text x="76.179329" y="162.79837" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="76.179329" y="162.79837" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Virtqueues</tspan></text></g><g><rect x="58.208" y="164.71" width="47.625" height="5.2917" ry="1.5259e-5" style="fill:#c3e8aa;stroke-width:.265;stroke:#000000"/><text x="76.452179" y="168.17548" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="76.452179" y="168.17548" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">I/O buffers</tspan></text></g></g></g><path d="m127 173.97-21.167 1e-5" style="fill:none;marker-end:url(#c);marker-start:url(#l);stroke-dasharray:1.05833327, 1.05833327;stroke-width:.26458;stroke:#000000"/><path d="m106.28 168.61 15.433.0673" style="fill:none;marker-end:url(#d);stroke-dasharray:1.05833327, 1.05833327;stroke-width:.26458;stroke:#000000"/><text x="110.86868" y="166.85257" style="fill:#000000;font-family:sans-serif;font-size:10.583px;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="110.86868" y="166.85257" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">polling</tspan></text><text x="112.17093" y="173.11574" style="fill:#000000;font-family:sans-serif;font-size:10.583px;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="112.17093" y="173.11574" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">DMA</tspan></text><text x="67.980347" y="228.13426" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="67.980347" y="228.13426" style="stroke-width:.26458">KVM</tspan></text><text x="69.351151" y="202.76837" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="69.351151" y="202.76837" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">callfd</tspan></text><text x="106.9275" y="200.63379" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="106.9275" y="200.63379" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">eventfd interrupt</tspan></text><path d="m166.69 184.55v17.198c-21.167 0-60.854 1e-5-82.021 1e-5" style="fill:none;marker-end:url(#e);stroke-dasharray:1.58999992, 1.58999992;stroke-width:.265;stroke:#000000"/><text x="72.494453" y="214.47757" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="72.494453" y="214.47757" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">irqfd</tspan></text><text x="23.784939" y="158.1282" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="23.784939" y="158.1282">Virtio-SCSI PCI</tspan><tspan x="23.784939" y="162.53793">driver</tspan></text><path d="m54.24 171.32h-10.583" style="fill:none;marker-end:url(#k);marker-start:url(#j);stroke-dasharray:0.79499996, 0.79499996;stroke-width:.265;stroke:#000000"/><text x="18.493273" y="148.83333" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="18.493273" y="148.83333" style="font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">VM</tspan></text><rect x="127" y="179.26" width="30.427" height="5.2917" style="fill:none;stroke-dasharray:1.05833328, 1.05833328;stroke-width:.26458;stroke:#000000"/><text x="128.16721" y="182.72755" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="128.16721" y="182.72755" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Unix domain socket</tspan></text><text x="104.54487" y="194.10464" style="fill:#000000;font-family:sans-serif;font-feature-settings:normal;font-size:3.5278px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;letter-spacing:0px;line-height:1.25;stroke-width:.26458;word-spacing:0px" xml:space="preserve"><tspan x="104.54487" y="194.10464" style="font-family:sans-serif;font-feature-settings:normal;font-size:2.8222px;font-variant-caps:normal;font-variant-ligatures:normal;font-variant-numeric:normal;stroke-width:.26458">Vhost-user messages</tspan></text><path d="m142.88 184.55v10.583h-58.208" style="fill:none;marker-end:url(#b);marker-start:url(#a);stroke-dasharray:1.58999992, 1.58999992;stroke-width:.265;stroke:#000000"/></g></svg>

doc/vhost_processing.md

+1 −49
Original line number Diff line number Diff line
@@ -53,55 +53,7 @@ One of major Vhost-user use cases is networking (DPDK) or storage (SPDK) 
offload in QEMU. The following diagram presents how QEMU-based VM

communicates with SPDK Vhost-SCSI device.



```

       +-------------------------------------QEMU-----------------------------+             +------------------------------------------SPDK vhost--------------------+

       |                                                                      |             |                                                                        |

       |  +---------------------------------VM-----------------------------+  |             |                           +-----------------------------------------+  |

       |  |                                                                |  |             |                           |                                         |  |

       |  |  +----------------------------------------------------------+  |  |             |                           |                                         |  |

       |  |  |                                                          |  |  |             |                           |                                         |  |

       |  |  |                               +--------------------------+--+--+-------------+------------+              |                                         |  |

       |  |  |                               |                                                           |              |                Vhost-SCSI               |  |

       |  |  |                               |                  Shared hugepage memory                   |              |                  device                 |  |

       |  |  |                               |                                                           |              |                                         |  |

       |  |  |                               |  +-----------------------------------------------------+  |              |                                         |  |

       |  |  |                               |  |                                                     |  |   polling    |                                         |  |

       |  |  |                               |  |                      Virtqueues                     +----------------->                                         |  |

       |  |  |   Virtio-SCSI PCI driver      |  |                                                     |  |              |  +-----------------------------------+  |  |

       |  |  |                               |  +-----------------------------------------------------+  |              |  |                                   |  |  |

       |  |  |                               |  |                                                     |  |    DMA       |  |  SPDK bdev(s)                     |  |  |

       |  |  |                               |  |                      I/O buffers                    <--------------------+  (NVMe, NVMf, Ceph RBD, PMEM)     |  |  |

+--------->  |                               |  |                                                     |  |              |  |                                   |  |  |

|      |  |  |                               |  +-----------------------------------------------------+  |              |  +-----------------------------------+  |  |

|      |  |  |                               |                                                           |              |                                         |  |

|      |  |  |                               +--------------------------+--+--+-------------+------------+              |  +----------------------+               |  |

|      |  |  |                                                          |  |  |             |                           |  |                      |               |  |

|      |  +--+--------^--+----------------------------------------------+--+  |             |                           |  |  Unix domain socket  |               |  |

|      |              |  |                                                    |             |                           |  |                      |               |  |

|      |  +-----------+--v-----------+-------------------------------------+  |             |                           |  +-------^--------------+               |  |

|      |  |                          |                                     |  |             |                           |          |                              |  |

|      |  |  Virtio-SCSI device      |  Vhost-user driver (master)         |  |             |                           +------------------------------------+----+  |

|      |  |                          |                                     |  |             |                                      |                         |       |

|      |  |                          |                                     |  |             +------------------------------------------------------------------------+

|      |  |                          |                                     |  |                                                    |                         |

|      |  |                          |                                     |  |                                                    |                         |

|      |  |                          |                                     |  |                Vhost-user messages                 |                         |

|      |  |                          |                                     <-------------------------------------------------------+                         |

|      |  |                          |                                     |  |                                                                              |

|      |  |                          |                    +----------------+  |                                                           eventfd interrupt  |

|      |  |                          |                    |     callfd     <---------------------------------------------------------------------------------+

|      |  +--------------------------+--------------------+---+------------+  |

|      |                                                      |               |

|      +----------------------------------------------------------------------+

|                                                             |

|                                                             |irqfd

|                                                             |

|                                                         +---v---+

|                                                         |       |

+---------------------------------------------------------+  KVM  |

                                                          |       |

                                                          +-------+

```

![QEMU/SPDK vhost data flow](img/qemu_vhost_data_flow.svg)



The irqfd mechanism isn't described in this document, as it KVM/QEMU-specific.

Briefly speaking, doing an eventfd_write on the callfd descriptor will