3 The DRM Lease Manager uses the DRM Lease feature, introduced in the Linux kernel version 4.15,
4 to partition display controller output resources between multiple processes.
6 For more information on the DRM lease functionality, please see the blog posts published by Keith
7 Packard, who developed the feature, at https://keithp.com/blogs/DRM-lease/
9 This repository contains a user space daemon to create and manage DRM leases, and distribute them
10 to client applications. This implementation is independent of any window system / compositor,
11 such as X11 or wayland, so can be used with clients that directly access a DRM device.
13 This repository also provides a library that clients can use to communicate with the DRM Lease Manager.
17 Build this repository requires a recent version of the [meson](https://mesonbuild.com/Getting-meson.html) build system.
19 The basic build procedure is as follows:
23 sudo ninja -C <build_dir> install
25 `<build_dir>` can be any directory name, but `build` is commonly used.
29 The drm-lease-manager configuration file allows the user to specify the mapping
30 of DRM connectors to DRM leases. The location of the configuration file can
31 be specified with the `-c` command line option.
33 The configuration file consists of a list of lease definitions, containing a name
34 of the lease and a list of the included connector names.
36 Each list entry is of the following form:
41 connectors=["connector 1", "connector 2"]
43 * Note: quotes around all string values are mandatory.
45 This will create a lease named `My lease` and add the two connectors `connector 1` and
46 `connector 2` to the lease.
47 If there is no connector with either of the names exists on the system, that name
48 will be omitted from the lease.
50 ### No configuration default
52 If no configuration file is specified one DRM lease will be created for each connector
53 on the DRM device (up to the number of available CRTCs).
55 The names of the DRM leases will have the following pattern:
57 <device>-<connector name>
59 So, for example, a DRM lease for the first LVDS device on the device `/dev/dri/card0` would be named
64 Once installed, running the following command will start the DRM Lease Manager daemon
66 drm-lease-manager [<path DRM device>]
68 If no DRM device is specified, `/dev/dri/card0` will be used.
69 More detailed options can be displayed by specifying the `-h` flag.
71 ### Dynamic lease transfer
73 When `drm-lease-manager` is started with the `-t` option, the
74 ownership of a leases resourses can be transfered from
75 one client to another.
77 This allows the ownership of the leased resources to be transferred
78 without the display being closed and the screen blanking.
79 `drm-lease-manager` handles the timing of the tranfser and manages the
80 references to the DRM device, so that the last framebuffer of
81 the old client stays on screen until the new client presents its first frame.
83 The transition can be completed without direct communication between the old
84 and new client applications, however, the client that the lease will be
85 transitioned *from* must be able to handle unexpected lease revokation.
86 Once the lease is revoked, all DRM API calls referring to the DRM
87 resources managed by the lease will fail with -ENOENT. The client
88 should be able to gracefully handle this condition by, for example,
89 pausing or shutting down its rendering operations.
93 The libdmclient handles all communication with the DRM Lease Manager and provides file descriptors that
94 can be used as if the DRM device was opened directly. Clients only need to replace their calls to
95 `drmOpen()` and `drmClose()` with the appropriate libdlmclient API calls.
97 The client library API is described in `dlmclient.h` in the `libdlmclient` directory.
99 If doxygen is available, building the repository will generate doxygen documentation in the
100 `<build_dir>/libdlmclient/docs/html` directory.
104 _Error handling has been omitted for brevity and clarity of examples._
106 #### Requesting a lease from the DRM Lease Manager
109 struct dlm_lease *lease = dlm_get_lease("card0-HDMI-A-1");
110 int drm_device_fd = dlm_lease_fd(lease);
113 `drm_device_fd` can now be used to access the DRM device
115 #### Releasing a lease
118 dlm_release_lease(lease);
121 **Note: `drm_device_fd` is not usable after calling `dlm_release_lease()`**
124 A runtime directory under the `/var` system directory is used by the drm-lease-manager and clients to
125 communicate with each other.
126 The default path is `/var/run/drm-lease-manager`, but can be changed by setting the `-Druntime_subdir`
127 option during configuration with `meson`.
129 The runtime directory can also be specified at runtime by setting the `DLM_RUNTIME_PATH` environment variable.