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man pages section 7: Standards, Environments, Macros, Character Sets, and Miscellany

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Updated: Wednesday, July 27, 2022

drm (7)


drm - Direct Rendering Manager


#include <xf86drm.h>


DRM(7)                     Direct Rendering Manager                     DRM(7)

       drm - Direct Rendering Manager

       #include <xf86drm.h>

       The Direct Rendering Manager (DRM) is a framework to manage Graphics
       Processing Units (GPUs). It is designed to support the needs of complex
       graphics devices, usually containing programmable pipelines well suited
       to 3D graphics acceleration. Furthermore, it is responsible for memory
       management, interrupt handling and DMA to provide a uniform interface
       to applications.

       In earlier days, the kernel framework was solely used to provide raw
       hardware access to privileged user-space processes which implement all
       the hardware abstraction layers. But more and more tasks were moved
       into the kernel. All these interfaces are based on ioctl(2) commands on
       the DRM character device. The libdrm library provides wrappers for
       these system-calls and many helpers to simplify the API.

       When a GPU is detected, the DRM system loads a driver for the detected
       hardware type. Each connected GPU is then presented to user-space via a
       character-device that is usually available as /dev/dri/card0 and can be
       accessed with open(2) and close(2). However, it still depends on the
       graphics driver which interfaces are available on these devices. If an
       interface is not available, the syscalls will fail with EINVAL.

       All DRM devices provide authentication mechanisms. Only a DRM-Master is
       allowed to perform mode-setting or modify core state and only one user
       can be DRM-Master at a time. See drmSetMaster(3) for information on how
       to become DRM-Master and what the limitations are. Other DRM users can
       be authenticated to the DRM-Master via drmAuthMagic(3) so they can
       perform buffer allocations and rendering.

       Managing connected monitors and displays and changing the current modes
       is called Mode-Setting. This is restricted to the current DRM-Master.
       Historically, this was implemented in user-space, but new DRM drivers
       implement a kernel interface to perform mode-setting called Kernel Mode
       Setting (KMS). If your hardware-driver supports it, you can use the KMS
       API provided by DRM. This includes allocating framebuffers, selecting
       modes and managing CRTCs and encoders. See drm-kms(7) for more.

   Memory Management
       The most sophisticated tasks for GPUs today is managing memory objects.
       Textures, framebuffers, command-buffers and all other kinds of commands
       for the GPU have to be stored in memory. The DRM driver takes care of
       managing all memory objects, flushing caches, synchronizing access and
       providing CPU access to GPU memory. All memory management is hardware
       driver dependent. However, two generic frameworks are available that
       are used by most DRM drivers. These are the Translation Table Manager
       (TTM) and the Graphics Execution Manager (GEM). They provide generic
       APIs to create, destroy and access buffers from user-space. However,
       there are still many differences between the drivers so driver-depedent
       code is still needed. Many helpers are provided in libgbm (Graphics
       Buffer Manager) from the mesa-project. For more information on DRM
       memory-management, see drm-memory(7).

       Bugs in this manual should be reported to
       under the "DRI" product, component "libdrm"

       See attributes(7) for descriptions of the following attributes:

       |Availability   | x11/library/libdrm |
       |Stability      | Volatile           |

       drm-kms(7), drm-memory(7), drmSetMaster(3), drmAuthMagic(3),
       drmAvailable(3), drmOpen(3)

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from

       Further information about this software can be found on the open source
       community website at https://dri.freedesktop.org/.

libdrm                          September 2012                          DRM(7)