(EE) Failed to load module "nv" (module does not exist, 0)

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When using the nouveau drivers, here is a sample excerpt from /var/log/Xorg.0.log:

[    47.274] (==) AIGLX enabled
[    47.274] (==) Matched nouveau as autoconfigured driver 0
[    47.274] (==) Matched nv as autoconfigured driver 1
[    47.274] (==) Matched nouveau as autoconfigured driver 2
[    47.274] (==) Matched nv as autoconfigured driver 3
[    47.274] (==) Matched modesetting as autoconfigured driver 4
[    47.274] (==) Matched fbdev as autoconfigured driver 5
[    47.274] (==) Matched vesa as autoconfigured driver 6
[    47.274] (==) Assigned the driver to the xf86ConfigLayout
[    47.274] (II) LoadModule: "nouveau"
[    47.274] (II) Loading /usr/lib64/xorg/modules/drivers/nouveau_drv.so
[    47.276] (II) Module nouveau: vendor="X.Org Foundation"
[    47.276] compiled for 1.18.4, module version = 1.0.12
[    47.276] Module class: X.Org Video Driver
[    47.276] ABI class: X.Org Video Driver, version 20.0
[    47.276] (II) LoadModule: "nv"
[    47.276] (WW) Warning, couldn't open module nv
[    47.276] (II) UnloadModule: "nv"
[    47.276] (II) Unloading nv
[    47.276] (EE) Failed to load module "nv" (module does not exist, 0)
[    47.276] (II) LoadModule: "modesetting"
[    47.276] (II) Loading /usr/lib64/xorg/modules/drivers/modesetting_drv.so
[    47.277] (II) Module modesetting: vendor="X.Org Foundation"
[    47.277] compiled for 1.18.4, module version = 1.18.4
[    47.277] Module class: X.Org Video Driver
[    47.277] ABI class: X.Org Video Driver, version 20.0
[    47.277] (II) LoadModule: "fbdev"
[    47.277] (WW) Warning, couldn't open module fbdev
[    47.277] (II) UnloadModule: "fbdev"
[    47.277] (II) Unloading fbdev
[    47.277] (EE) Failed to load module "fbdev" (module does not exist, 0)
[    47.277] (II) LoadModule: "vesa"
[    47.277] (WW) Warning, couldn't open module vesa
[    47.277] (II) UnloadModule: "vesa"
[    47.277] (II) Unloading vesa
[    47.277] (EE) Failed to load module "vesa" (module does not exist, 0)
[    47.277] (II) NOUVEAU driver
[    47.277] (II) NOUVEAU driver for NVIDIA chipset families :
[    47.277] RIVA TNT        (NV04)
[    47.277] RIVA TNT2       (NV05)
[    47.277] GeForce 256     (NV10)
[    47.277] GeForce 2       (NV11, NV15)
[    47.278] GeForce 4MX     (NV17, NV18)
[    47.278] GeForce 3       (NV20)
[    47.278] GeForce 4Ti     (NV25, NV28)
[    47.278] GeForce FX      (NV3x)
[    47.278] GeForce 6       (NV4x)
[    47.278] GeForce 7       (G7x)
[    47.278] GeForce 8       (G8x)
[    47.278] GeForce GTX 200 (NVA0)
[    47.278] GeForce GTX 400 (NVC0)
[    47.278] (II) modesetting: Driver for Modesetting Kernel Drivers: kms
[    47.278] (++) using VT number 7

[    47.279] (II) [drm] nouveau interface version: 1.3.1
[    47.279] (EE) Unknown chipset: NV117
[    47.279] (II) [drm] nouveau interface version: 1.3.1
[    47.279] (EE) Unknown chipset: NV117
[    47.279] (II) [drm] nouveau interface version: 1.3.1
[    47.279] (EE) Unknown chipset: NV117
[    47.279] (II) [drm] nouveau interface version: 1.3.1
[    47.279] (EE) Unknown chipset: NV117
[    47.279] (II) [drm] nouveau interface version: 1.3.1
[    47.279] (EE) Unknown chipset: NV117
[    47.279] (II) modeset(0): using drv /dev/dri/card0
[    47.280] (II) modeset(0): Creating default Display subsection in Screen section

Solution on a gentoo system: install the package x11-drivers/xf86-video-nv.

Remaining questions that have yet to be answered in this wiki:
Why would Xorg need the nv driver (an old 2D driver) when the nouveau driver is already loaded? Does Xorg need the two drivers?