buildroot编译内核启动报错：Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)问题解决

[drm:i915_firmware_load_error_print] *ERROR* failed to load firmware i915/skl_dmc_ver1.bin (0)
[    0.313887] [drm:i915_firmware_load_error_print] *ERROR* The driver is built-in, so to load the firmware you need to
[    0.313887] include it either in the kernel (see CONFIG_EXTRA_FIRMWARE) or
[    0.313887] in your initrd/initramfs image.
[    0.618978] [drm:intel_guc_ucode_init] *ERROR* Failed to fetch GuC firmware from i915/skl_guc_ver4.bin (error -2)
[    0.743019] [drm:i915_gem_init_hw] *ERROR* Failed to initialize GuC, error -5 (ignored)
[    0.888525] hdaudio hdaudioC0D2: Unable to bind the codec
[    1.004739] usb usb1-port5: over-current condition
[    1.183738] usb usb1-port6: over-current condition
[    1.242124] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[    1.341052] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.4.283 #1
[    1.412915] Hardware name: 360WS Default string/RT5140, BIOS 360WS-LY236-5140-20180130 01/30/2018
[    1.519094]  0000000000000000 ffff880264287de0 ffffffff818d7847 ffff880263495000
[    1.608012]  ffffffff81b94590 ffff880264287e58 ffffffff818ca0dd ffffffff00000010
[    1.696931]  ffff880264287e68 ffff880264287e08 0000000400000001 ffff880264287e78
[    1.785847] Call Trace:
[    1.815075]  [<ffffffff818d7847>] dump_stack+0x57/0x6d
[    1.876534]  [<ffffffff818ca0dd>] panic+0xbb/0x1ff
[    1.933838]  [<ffffffff81f3d2da>] mount_block_root+0x174/0x1ee
[    2.003625]  [<ffffffff81f3d443>] mount_root+0xef/0xf8
[    2.065082]  [<ffffffff81f3d586>] prepare_namespace+0x13a/0x172
[    2.135903]  [<ffffffff81f3cfa7>] kernel_init_freeable+0x1c4/0x1d9
[    2.209846]  [<ffffffff818f2532>] ? rest_init+0x79/0x79
[    2.272348]  [<ffffffff818f253b>] kernel_init+0x9/0xde
[    2.333810]  [<ffffffff818f7d15>] ret_from_fork+0x55/0x80
[    2.398392]  [<ffffffff818f2532>] ? rest_init+0x79/0x79
[    2.460942] Kernel Offset: disabled
[    2.502701] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

解决办法：
1）内核编译“Kernel binary format”选择bzImage镜像：

2）使能buildroot文件系统的RAM FS编译到内核bzImage；“initial RAM filesystem…”选择开启后，“cpio the root filesystem…”会被自动强制选中开启：

3）关联的，内核代码的General setup里“Initial RAM filesystem…”也会被自动强制选中开启，路径设置的是buildroot的/output/images/rootfs.cpio，被buildroot编译cpio归档的文件系统镜像：

4）grub启动bzImage项设置大致如下：

[shell /root]$cat /boot/grub/grub.conf
default 0
timeout 3
title buildroot
root (hd0,0)
kernel /bzImage root=/dev/sda1 ro quiet console=ttyS0,9600

ram filesystem内存文件系统编译进了bzImage内核镜像，启动分区为第一分区，其中“root=/dev/sda1”可有可无，不影响启动；