文章目录
- 1. 前言
- 2. ubi rootfs 加载故障现场
- 3. 故障分析与解决
- 4. 参考资料
1. 前言
限于作者能力水平，本文可能存在谬误，因此而给读者带来的损失，作者不做任何承诺。
2. ubi rootfs 加载故障现场
问题故障内核日志如下：
Starting kernel ...
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 4.19.94-g1194fe2-dirty (bill@bill-virtual-machine) (gcc version 5.3.1 20160113 (Linaro GCC 5.3-2016.02)) #21 PREEMPT Tue Jun 4 10:18:44 CST 2024
[ 0.000000] CPU: ARMv7 Processor [413fc082] revision 2 (ARMv7), cr=10c5387d
......
[ 0.000000] Kernel command line: console=ttyO0,115200n8 root=ubi0:rootfs rw ubi.mtd=NAND.rootfs,2048 rootfstype=ubifs rootwait=1
......
[ 1.713970] nand: device found, Manufacturer ID: 0x2c, Chip ID: 0xda
[ 1.720358] nand: Micron MT29F2G08AAD
[ 1.724091] nand: 256 MiB, SLC, erase size: 128 KiB, page size: 2048, OOB size: 64
[ 1.731736] nand: using OMAP_ECC_BCH8_CODE_HW ECC scheme
[ 1.737188] 11 fixed-partitions partitions found on MTD device omap2-nand.0
[ 1.744196] Creating 11 MTD partitions on "omap2-nand.0":
[ 1.749624] 0x000000000000-0x000000020000 : "NAND.SPL"
[ 1.755917] 0x000000020000-0x000000040000 : "NAND.SPL.backup1"
[ 1.762654] 0x000000040000-0x000000060000 : "NAND.SPL.backup2"
[ 1.769446] 0x000000060000-0x000000080000 : "NAND.SPL.backup3"
[ 1.776214] 0x000000080000-0x0000000c0000 : "NAND.u-boot-spl-os"
[ 1.783272] 0x0000000c0000-0x0000001c0000 : "NAND.u-boot"
[ 1.790358] 0x0000001c0000-0x0000001e0000 : "NAND.u-boot-env"
[ 1.797050] 0x0000001e0000-0x000000200000 : "NAND.u-boot-env.backup1"
[ 1.804438] 0x000000200000-0x000000a00000 : "NAND.kernel"
[ 1.818114] 0x000000a00000-0x00000e000000 : "NAND.rootfs"
[ 2.024110] 0x00000e000000-0x000010000000 : "NAND.userdata"
......
[ 2.162435] ubi0: attaching mtd9
[ 2.166572] ubi0 error: validate_ec_hdr: bad VID header offset 512, expected 2048
[ 2.174146] ubi0 error: validate_ec_hdr: bad EC header
[ 2.179304] Erase counter header dump:
[ 2.183118] magic 0x55424923
[ 2.186881] version 1
[ 2.189856] ec 0
[ 2.192829] vid_hdr_offset 512
[ 2.195994] data_offset 2048
[ 2.199232] image_seq 2007489760
[ 2.203004] hdr_crc 0xbe9cfce9
[ 2.206763] erase counter header hexdump:
[ 2.210810] CPU: 0 PID: 1 Comm: swapper Not tainted 4.19.94-g1194fe2-dirty #21
[ 2.218072] Hardware name: Generic AM33XX (Flattened Device Tree)
[ 2.224199] Backtrace:
[ 2.226668] [<c010bfe4>] (dump_backtrace) from [<c010c2b4>] (show_stack+0x18/0x1c)
[ 2.234283] r7:00000000 r6:00000000 r5:cf04c000 r4:cf675c00
[ 2.239970] [<c010c29c>] (show_stack) from [<c09531b4>] (dump_stack+0x24/0x28)
[ 2.247237] [<c0953190>] (dump_stack) from [<c064da18>] (validate_ec_hdr+0xa0/0xe4)
[ 2.254942] [<c064d978>] (validate_ec_hdr) from [<c064e600>] (ubi_io_read_ec_hdr+0x1b4/0x204)
[ 2.263546] r7:cf04c000 r6:55424923 r5:cf675c00 r4:00000000
[ 2.269233] [<c064e44c>] (ubi_io_read_ec_hdr) from [<c0653a40>] (ubi_attach+0x1b8/0x1464)
[ 2.277464] r10:cf76f000 r9:00000000 r8:00000000 r7:cf675c00 r6:cf04c000 r5:cf734a00
[ 2.285336] r4:cf736240
[ 2.287884] [<c0653888>] (ubi_attach) from [<c0647f78>] (ubi_attach_mtd_dev+0x42c/0xbc4)
[ 2.296023] r10:00020000 r9:cf721400 r8:c0e03048 r7:00000000 r6:cf721400 r5:cf04c000
[ 2.303893] r4:0000103f
[ 2.306445] [<c0647b4c>] (ubi_attach_mtd_dev) from [<c0d26378>] (ubi_init+0x184/0x22c)
[ 2.314410] r10:c0e370cc r9:c0c2a8e8 r8:c0c2a8bc r7:c0e85e64 r6:cf721400 r5:c0e85e68
[ 2.322270] r4:00000000
[ 2.324830] [<c0d261f4>] (ubi_init) from [<c01026ac>] (do_one_initcall+0x5c/0x1a4)
[ 2.332435] r10:00000008 r9:c0e03048 r8:00000000 r7:c0d261f4 r6:ffffe000 r5:c0e4f140
[ 2.340306] r4:c0e4f140
[ 2.342859] [<c0102650>] (do_one_initcall) from [<c0d00f34>] (kernel_init_freeable+0x13c/0x1d4)
[ 2.351610] r9:c0d00620 r8:000000f8 r7:c0d3e834 r6:c0d51d64 r5:c0e4f140 r4:c0e4f140
[ 2.359404] [<c0d00df8>] (kernel_init_freeable) from [<c09689d8>] (kernel_init+0x10/0x118)
[ 2.367716] r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:c09689c8
[ 2.375587] r4:00000000
[ 2.378132] [<c09689c8>] (kernel_init) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
[ 2.385743] Exception stack(0xcf051fb0 to 0xcf051ff8)
[ 2.390816] 1fa0: 00000000 00000000 00000000 00000000
[ 2.399040] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 2.407263] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[ 2.413914] r5:c09689c8 r4:00000000
[ 2.417506] ubi0 error: ubi_io_read_ec_hdr: validation failed for PEB 0
[ 2.424265] ubi0 error: ubi_attach_mtd_dev: failed to attach mtd9, error -22
[ 2.431373] UBI error: cannot attach mtd9
[ 2.436450] input: volume_keys@0 as /devices/platform/volume_keys@0/input/input0
[ 2.444593] omap_rtc 44e3e000.rtc: setting system clock to 2000-01-01 00:00:00 UTC (946684800)
[ 2.453894] ALSA device list:
[ 2.456888] #0: crt_audio_bus
[ 2.460684] VFS: Cannot open root device "ubi0:rootfs" or unknown-block(0,0): error -19
[ 2.468832] Please append a correct "root=" boot option; here are the available partitions:
[ 2.477272] 0100 65536 ram0
[ 2.477276] (driver?)
[ 2.483432] 0101 65536 ram1
[ 2.483435] (driver?)
[ 2.489561] 0102 65536 ram2
[ 2.489563] (driver?)
[ 2.495704] 0103 65536 ram3
[ 2.495706] (driver?)
[ 2.501830] 0104 65536 ram4
[ 2.501832] (driver?)
[ 2.507970] 0105 65536 ram5
[ 2.507972] (driver?)
[ 2.514109] 0106 65536 ram6
[ 2.514111] (driver?)
[ 2.520236] 0107 65536 ram7
[ 2.520238] (driver?)
[ 2.526375] 0108 65536 ram8
[ 2.526378] (driver?)
[ 2.532502] 0109 65536 ram9
[ 2.532504] (driver?)
[ 2.538642] 010a 65536 ram10
[ 2.538645] (driver?)
[ 2.544868] 010b 65536 ram11
[ 2.544870] (driver?)
[ 2.551083] 010c 65536 ram12
[ 2.551085] (driver?)
[ 2.557309] 010d 65536 ram13
[ 2.557311] (driver?)
[ 2.563533] 010e 65536 ram14
[ 2.563536] (driver?)
[ 2.569748] 010f 65536 ram15
[ 2.569751] (driver?)
[ 2.575982] 1f00 128 mtdblock0
[ 2.575984] (driver?)
[ 2.582546] 1f01 128 mtdblock1
[ 2.582548] (driver?)
[ 2.589122] 1f02 128 mtdblock2
[ 2.589125] (driver?)
[ 2.595704] 1f03 128 mtdblock3
[ 2.595706] (driver?)
[ 2.602266] 1f04 256 mtdblock4
[ 2.602268] (driver?)
[ 2.608841] 1f05 1024 mtdblock5
[ 2.608844] (driver?)
[ 2.615416] 1f06 128 mtdblock6
[ 2.615418] (driver?)
[ 2.621980] 1f07 128 mtdblock7
[ 2.621983] (driver?)
[ 2.628556] 1f08 8192 mtdblock8
[ 2.628559] (driver?)
[ 2.635130] 1f09 219136 mtdblock9
[ 2.635133] (driver?)
[ 2.641695] 1f0a 32768 mtdblock10
[ 2.641697] (driver?)
[ 2.648358] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 2.656667] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---3. 故障分析与解决
内核日志信息：
[ 2.162435] ubi0: attaching mtd9
[ 2.166572] ubi0 error: validate_ec_hdr: bad VID header offset 512, expected 2048
[ 2.174146] ubi0 error: validate_ec_hdr: bad EC header结合前面的 NAND 分区日志分析，可以知道，mtd9 对应分区 "NAND.rootfs"，所以实在挂载 rootfs 过程中出错了。通过内核导出的出错时的调用栈信息，定位到出错代码路径如下(内核版本为 4.19.94)：
kernel_init()
kernel_init_freeable()
do_basic_setup()
do_initcalls()
...
do_one_initcall()
ubi_init()/* drivers/mtd/ubi/build.c */
static int __init ubi_init(void)
{
...
/* Attach MTD devices */
/* mtd_dev_param[] 和 mtd_devs 的设置过程，见后文的 ubi_mtd_param_parse() 分析 */
for (i = 0; i < mtd_devs; i++) {
struct mtd_dev_param *p = &mtd_dev_param[i];
struct mtd_info *mtd;
...
mtd = open_mtd_device(p->name);
...
mutex_lock(&ubi_devices_mutex);
err = ubi_attach_mtd_dev(mtd, p->ubi_num,
p->vid_hdr_offs, p->max_beb_per1024);
mutex_unlock(&ubi_devices_mutex);
...
}
...
}
int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num,
int vid_hdr_offset, int max_beb_per1024)
{
struct ubi_device *ubi;
...
...
ubi = kzalloc(sizeof(struct ubi_device), GFP_KERNEL);
...
ubi->mtd = mtd;
ubi->ubi_num = ubi_num;
ubi->vid_hdr_offset = vid_hdr_offset;
ubi->autoresize_vol_id = -1;
...
err = io_init(ubi, max_beb_per1024);
...
err = ubi_attach(ubi, 0);
...
/* Make device "available" before it becomes accessible via sysfs */
ubi_devices[ubi_num] = ubi;
...
}
static int io_init(struct ubi_device *ubi, int max_beb_per1024)
{
...
ubi->peb_size = ubi->mtd->erasesize;
ubi->peb_count = mtd_div_by_eb(ubi->mtd->size, ubi->mtd);
ubi->flash_size = ubi->mtd->size;
...
ubi->leb_size = ubi->peb_size - ubi->leb_start; /* (2) */
...
}
/* drivers/mtd/ubi/attach.c */
int ubi_attach(struct ubi_device *ubi, int force_scan)
{
...
err = scan_all(ubi, ai, 0);
...
}
static int scan_all(struct ubi_device *ubi, struct ubi_attach_info *ai,
int start)
{
...
for (pnum = start; pnum < ubi->peb_count; pnum++) {
...
err = scan_peb(ubi, ai, pnum, false);
...
}
...
}
static int scan_peb(struct ubi_device *ubi, struct ubi_attach_info *ai,
int pnum, bool fast)
{
...
err = ubi_io_read_ec_hdr(ubi, pnum, ech, 0);
...
}
/* drivers/mtd/ubi/io.c */
int ubi_io_read_ec_hdr(struct ubi_device *ubi, int pnum,
struct ubi_ec_hdr *ec_hdr, int verbose)
{
...
/* And of course validate what has just been read from the media */
err = validate_ec_hdr(ubi, ec_hdr);
...
}
static int validate_ec_hdr(const struct ubi_device *ubi,
const struct ubi_ec_hdr *ec_hdr)
{
...
int vid_hdr_offset, leb_start;
...
vid_hdr_offset = be32_to_cpu(ec_hdr->vid_hdr_offset);
...
/* (1) */
if (vid_hdr_offset != ubi->vid_hdr_offset) {
ubi_err(ubi, "bad VID header offset %d, expected %d",
vid_hdr_offset, ubi->vid_hdr_offset);
goto bad;
}
...
bad:
ubi_err(ubi, "bad EC header");
ubi_dump_ec_hdr(ec_hdr);
dump_stack();
return 1;
}问题出在 validate_ec_hdr() 函数位置 (1) 处，由于 vid_hdr_offset 和 ubi->vid_hdr_offset 不相等导致。vid_hdr_offset 来自 ec_hdr->vid_hdr_offset；从上面分析的代码分析，进一步得知 ec_hdr->vid_hdr_offset 来自于 ubi_io_read_ec_hdr() 从设备读取的信息，这个信息是后文提到的 ubinize 工具将 rootfs.ubifs 打包到 rootfs.ubi 镜像是插入的 UBI 卷管理信息 superblock。这里暂时不细表，留待后文分析。另外一个信息 ubi->vid_hdr_offset 来自内核命令行参数 ubi.mtd=NAND.rootfs,2048，其赋值的代码流程如下：
start_kernel()
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, NULL, &unknown_bootoption);
...
ubi_mtd_param_parse()/* drivers/mtd/ubi/build.c */
/*
* 本文中用来解析 ubi.mtd=NAND.rootfs,2048
* @val: "NAND.rootfs,2048"
*/
static int ubi_mtd_param_parse(const char *val, const struct kernel_param *kp)
{
...
p = &mtd_dev_param[mtd_devs];
strcpy(&p->name[0], tokens[0]); /* @p->name: "NAND.rootfs" */
token = tokens[1];
if (token) {
p->vid_hdr_offs = bytes_str_to_int(token); /* @p->vid_hdr_offs: 2048 */
...
}
...
mtd_devs += 1;
return 0;
}
/*
* 定义解析 ubi.mtd=XXX 的接口 ubi_mtd_param_parse(),
* 如用来解析 ubi.mtd=NAND.rootfs,2048 。
*/
module_param_call(mtd, ubi_mtd_param_parse, NULL, NULL, 0400);ubi->vid_hdr_offset 的设置过程在 ubi_init() 调用之前完成。说完了 ubi->vid_hdr_offset 的设置过程，继续看在 UBI 根文件系统 rootfs.ubi 的构建过程中，对 ec_hdr->vid_hdr_offset 信息的填充过程。本文的UBI 根文件系统镜像 rootfs.ubi通过 buildroot 工具构建，其过程简单来讲，就是先通过 mkfs.ubifs 生成一个 rootfs.ubifs 文件，然后再通过工具 ubinize 将 rootfs.ubifs 打包成 UBI 根文件系统镜像 rootfs.ubi：
mkfs.ubifs ubinize
根文件系统目录树 ----------> rootfs.ubifs --------> rootfs.ubimkfs.ubifs 的构建的 rootfs.ubifs 文件，可以理解为根文件系统目录树的打包；而 ubinize 工具将 rootfs.ubifs 打包为 UBI 根文件系统镜像 rootfs.ubi 文件时，增加了包含 struct ubi_ec_hdr 头部信息等的 UBI 卷管理信息，rootfs.ubifs 无法直接作为烧录进设备分区的镜像，只有包含了 UBI 卷管理信息的 rootfs.ubi 才能烧录进设备分区，作为系统的根文件系统来启动。前面内核日志报错信息：
[ 2.166572] ubi0 error: validate_ec_hdr: bad VID header offset 512, expected 2048问题的根本原因在于：内核命令行参数 ubi.mtd=NAND.rootfs,2048 中的 2048 和 rootfs.ubifs 打包头部信息 struct ubi_ec_hdr::vid_hdr_offset 值 512(ubinize 工具给的默认值) 不匹配造成的。ubinize 工具的 -O 选项可以指定 struct ubi_ec_hdr::vid_hdr_offset 值。从 buildroot 工具 ubinize 打包过程文件 fs/ubifs/ubi.mk 片段：
...
UBI_UBINIZE_OPTS += $(call qstrip,$(BR2_TARGET_ROOTFS_UBI_OPTS))
...
define ROOTFS_UBI_CMD
sed 's;BR2_ROOTFS_UBIFS_PATH;$@fs;' \
$(UBINIZE_CONFIG_FILE_PATH) > $(BUILD_DIR)/ubinize.cfg
$(HOST_DIR)/usr/sbin/ubinize -o $@ $(UBI_UBINIZE_OPTS) $(BUILD_DIR)/ubinize.cfg
rm $(BUILD_DIR)/ubinize.cfg
endef得知可以通过 BR2_TARGET_ROOTFS_UBI_OPTS 配置给 ubinize 工具传递参数，运行 make menuconfig ，按如下修改 buildroot 配置 BR2_TARGET_ROOTFS_UBI_OPTS，给 ubinize 工具传递 -O 1024 参数，修改 打包头部信息 struct ubi_ec_hdr::vid_hdr_offset 值为 1024：
重新编译生成 rootfs.ubi，烧录并启动运行，看问题是否解决了：
[ 2.162404] ubi0: attaching mtd9
[ 2.817587] ubi0: scanning is finished
[ 2.841285] ubi0: volume 0 ("rootfs") re-sized from 83 to 1668 LEBs
[ 2.848341] ubi0: attached mtd9 (name "NAND.rootfs", size 214 MiB)
[ 2.854613] ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
[ 2.861516] ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 512
[ 2.868259] ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
[ 2.875260] ubi0: good PEBs: 1711, bad PEBs: 1, corrupted PEBs: 0
[ 2.881377] ubi0: user volume: 1, internal volumes: 1, max. volumes count: 128
[ 2.888641] ubi0: max/mean erase counter: 1/0, WL threshold: 4096, image sequence number: 425578287
[ 2.897735] ubi0: available PEBs: 0, total reserved PEBs: 1711, PEBs reserved for bad PEB handling: 39
[ 2.907100] ubi0: background thread "ubi_bgt0d" started, PID 65
......
[ 2.965365] UBIFS error (ubi0:0 pid 1): ubifs_read_superblock: LEB size mismatch: 129024 in superblock, 126976 real
[ 2.992980] UBIFS error (ubi0:0 pid 1): ubifs_read_superblock: bad superblock, error 1
[ 3.000933] magic 0x6101831
[ 3.004623] crc 0x3375ce2d
[ 3.008386] node_type 6 (superblock node)
[ 3.012931] group_type 0 (no node group)
[ 3.017314] sqnum 1
[ 3.020289] len 4096
[ 3.023537] key_hash 0 (R5)
[ 3.026950] key_fmt 0 (simple)
[ 3.030709] flags 0x0
[ 3.033870] big_lpt 0
[ 3.036845] space_fixup 0
[ 3.039818] min_io_size 2048
[ 3.043063] leb_size 129024
[ 3.046474] leb_cnt 1668
[ 3.049709] max_leb_cnt 2048
[ 3.052956] max_bud_bytes 8388608
[ 3.056454] log_lebs 5
[ 3.059429] lpt_lebs 2
[ 3.062403] orph_lebs 1
[ 3.065387] jhead_cnt 1
[ 3.068362] fanout 8
[ 3.071335] lsave_cnt 256
[ 3.074495] default_compr 0
[ 3.077470] rp_size 0
[ 3.080443] rp_uid 0
[ 3.083427] rp_gid 0
[ 3.086402] fmt_version 4
[ 3.089378] time_gran 1000000000
[ 3.093151] UUID 9FC73AE3-A0BA-41C8-8615-2B75694BB8CD
[ 3.204172] UBIFS error (ubi0:0 pid 1): ubifs_read_superblock: LEB size mismatch: 129024 in superblock, 126976 real
[ 3.222987] UBIFS error (ubi0:0 pid 1): ubifs_read_superblock: bad superblock, error 1
[ 3.230940] magic 0x6101831
[ 3.234647] crc 0x3375ce2d
[ 3.238408] node_type 6 (superblock node)
[ 3.242993] group_type 0 (no node group)
[ 3.247364] sqnum 1
[ 3.250338] len 4096
[ 3.253591] key_hash 0 (R5)
[ 3.257003] key_fmt 0 (simple)
[ 3.260762] flags 0x0
[ 3.263923] big_lpt 0
[ 3.266897] space_fixup 0
[ 3.269872] min_io_size 2048
[ 3.273117] leb_size 129024
[ 3.276528] leb_cnt 1668
[ 3.279765] max_leb_cnt 2048
[ 3.283011] max_bud_bytes 8388608
[ 3.286509] log_lebs 5
[ 3.289484] lpt_lebs 2
[ 3.292458] orph_lebs 1
[ 3.295441] jhead_cnt 1
[ 3.298417] fanout 8
[ 3.301390] lsave_cnt 256
[ 3.304548] default_compr 0
[ 3.307522] rp_size 0
[ 3.310496] rp_uid 0
[ 3.313479] rp_gid 0
[ 3.316454] fmt_version 4
[ 3.319429] time_gran 1000000000
[ 3.323199] UUID 9FC73AE3-A0BA-41C8-8615-2B75694BB8CD
[ 3.433193] List of all partitions:
[ 3.436713] 0100 65536 ram0
[ 3.436716] (driver?)
[ 3.442843] 0101 65536 ram1
[ 3.442845] (driver?)
[ 3.463000] 0102 65536 ram2
[ 3.463004] (driver?)
[ 3.469132] 0103 65536 ram3
[ 3.469135] (driver?)
[ 3.492961] 0104 65536 ram4
[ 3.492964] (driver?)
[ 3.499093] 0105 65536 ram5
[ 3.499095] (driver?)
[ 3.512959] 0106 65536 ram6
[ 3.512961] (driver?)
[ 3.519087] 0107 65536 ram7
[ 3.519090] (driver?)
[ 3.542960] 0108 65536 ram8
[ 3.542962] (driver?)
[ 3.549089] 0109 65536 ram9
[ 3.549091] (driver?)
[ 3.562956] 010a 65536 ram10
[ 3.562959] (driver?)
[ 3.569173] 010b 65536 ram11
[ 3.569175] (driver?)
[ 3.582961] 010c 65536 ram12
[ 3.582964] (driver?)
[ 3.589178] 010d 65536 ram13
[ 3.589180] (driver?)
[ 3.612959] 010e 65536 ram14
[ 3.612961] (driver?)
[ 3.619175] 010f 65536 ram15
[ 3.619177] (driver?)
[ 3.632970] 1f00 128 mtdblock0
[ 3.632974] (driver?)
[ 3.639537] 1f01 128 mtdblock1
[ 3.639540] (driver?)
[ 3.662959] 1f02 128 mtdblock2
[ 3.662962] (driver?)
[ 3.669524] 1f03 128 mtdblock3
[ 3.669527] (driver?)
[ 3.682960] 1f04 256 mtdblock4
[ 3.682963] (driver?)
[ 3.689526] 1f05 1024 mtdblock5
[ 3.689529] (driver?)
[ 3.712959] 1f06 128 mtdblock6
[ 3.712962] (driver?)
[ 3.719526] 1f07 128 mtdblock7
[ 3.719528] (driver?)
[ 3.732960] 1f08 8192 mtdblock8
[ 3.732963] (driver?)
[ 3.739526] 1f09 219136 mtdblock9
[ 3.739529] (driver?)
[ 3.762959] 1f0a 32768 mtdblock10
[ 3.762962] (driver?)
[ 3.769608] No filesystem could mount root, tried:
[ 3.769610] ubifs
[ 3.782955]
[ 3.786470] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 3.794779] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) ]---从内核日志看到，之前的问题没有了，但又有了新的问题。根据内核日志，分析下代码流程(对代码细节不感兴趣的读者，可以直接跳过)：
/* 1. 解析内核命令行参数: root=ubi0:rootfs rw rootfstype=ubifs rootwait=1 */
start_kernel()
after_dashes = parse_args("Booting kernel",
static_command_line, __start___param,
__stop___param - __start___param,
-1, -1, NULL, &unknown_bootoption);
...
unknown_bootoption()
obsolete_checksetup(param)
p->setup_func(line + n) = root_dev_setup(), rootwait_setup(), fs_names_setup()
/* init/do_mounts.c */
int root_mountflags = MS_RDONLY | MS_SILENT;
static int __init readwrite(char *str)
{
if (*str)
return 0;
root_mountflags &= ~MS_RDONLY; /* @root_mountflags: MS_SILENT */
return 1;
}
__setup("rw", readwrite);
static int __init root_dev_setup(char *line)
{
/* @saved_root_name: "ubi0:rootfs" */
strlcpy(saved_root_name, line, sizeof(saved_root_name));
return 1;
}
__setup("root=", root_dev_setup);
static int __init rootwait_setup(char *str)
{
if (*str)
return 0;
root_wait = 1; /* @root_wait: 1 */
return 1;
}
__setup("rootwait", rootwait_setup);
static char * __initdata root_fs_names;
static int __init fs_names_setup(char *str)
{
root_fs_names = str; /* @root_fs_names: "ubifs" */
return 1;
}
__setup("rootfstype=", fs_names_setup);start_kernel()
rest_init()
pid = kernel_thread(kernel_init, NULL, CLONE_FS); /* 启动初始化线程 */
kernel_init()
kernel_init_freeable()
prepare_namespace()
/* init/do_mounts.c */
void __init prepare_namespace(void)
{
if (saved_root_name[0]) { /* @saved_root_name: "ubi0:rootfs" */
root_device_name = saved_root_name;
if (!strncmp(root_device_name, "mtd", 3) ||
!strncmp(root_device_name, "ubi", 3)) {
mount_block_root(root_device_name, root_mountflags); /* 挂载 rootfs */
goto out;
}
}
...
out:
devtmpfs_mount("dev");
ksys_mount(".", "/", NULL, MS_MOVE, NULL);
ksys_chroot(".");
}
/* 挂载 rootfs */
void __init mount_block_root(char *name, int flags)
{
...
for (p = fs_names; *p; p += strlen(p)+1) {
int err = do_mount_root(name, p, flags, root_mount_data);
switch (err) {
case 0:
goto out; /* 成功挂载 rootfs */
case -EACCES:
case -EINVAL:
continue;
}
}
...
out:
...
}
/*
* @name : "ubi0:rootfs"
* @fs : "ubifs"
* @flags: MS_SILENT
* @data : NULL
*/
static int __init do_mount_root(char *name, char *fs, int flags, void *data)
{
struct super_block *s;
int err = ksys_mount(name, "/root", fs, flags, data);
...
}
/* fs/namespace.c */
int ksys_mount(char __user *dev_name, char __user *dir_name, char __user *type,
unsigned long flags, void __user *data)
{
...
ret = do_mount(kernel_dev, dir_name, kernel_type, flags, options);
...
}
long do_mount(const char *dev_name, const char __user *dir_name,
const char *type_page, unsigned long flags, void *data_page)
{
...
if (flags & MS_REMOUNT)
retval = do_remount(...);
else if (flags & MS_BIND)
retval = do_loopback(...);
else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
retval = do_change_type(...);
else if (flags & MS_MOVE)
retval = do_move_mount(...);
else
retval = do_new_mount(&path, type_page, sb_flags, mnt_flags,
dev_name, data_page);
...
}
static int do_new_mount(struct path *path, const char *fstype, int sb_flags,
int mnt_flags, const char *name, void *data)
{
struct file_system_type *type;
struct vfsmount *mnt;
...
type = get_fs_type(fstype); /* @type: &ubifs_fs_type */
...
mnt = vfs_kern_mount(type, sb_flags, name, data);
...
put_filesystem(type);
...
}
struct vfsmount *
vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
{
struct mount *mnt;
struct dentry *root;
...
mnt = alloc_vfsmnt(name);
...
root = mount_fs(type, flags, name, data);
mnt->mnt.mnt_root = root;
mnt->mnt.mnt_sb = root->d_sb;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
mnt->mnt_parent = mnt;
lock_mount_hash();
list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
unlock_mount_hash();
return &mnt->mnt;
}
/* fs/super.c */
struct dentry *
mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
{
struct dentry *root;
struct super_block *sb;
...
...
root = type->mount(type, flags, name, data); /* ubifs_mount() */
...
sb = root->d_sb;
...
return root;
...
}/* fs/ubifs/super.c */
static struct dentry *ubifs_mount(struct file_system_type *fs_type, int flags,
const char *name, void *data)
{
struct ubi_volume_desc *ubi;
struct ubifs_info *c;
struct super_block *sb;
...
/*
* Get UBI device number and volume ID. Mount it read-only so far
* because this might be a new mount point, and UBI allows only one
* read-write user at a time.
*/
ubi = open_ubi(name, UBI_READONLY);
...
c = alloc_ubifs_info(ubi);
...
sb = sget(fs_type, sb_test, sb_set, flags, c);
...
if (sb->s_root) {
...
} else {
err = ubifs_fill_super(sb, data, flags & SB_SILENT ? 1 : 0);
...
}
/* 'fill_super()' opens ubi again so we must close it here */
ubi_close_volume(ubi);
return dget(sb->s_root);
...
}
static struct ubi_volume_desc *open_ubi(const char *name, int mode)
{
struct ubi_volume_desc *ubi;
...
...
/* First, try to open using the device node path method */
ubi = ubi_open_volume_path(name, mode);
...
}
struct ubi_volume_desc *ubi_open_volume_path(const char *pathname, int mode)
{
...
if (vol_id >= 0 && ubi_num >= 0)
return ubi_open_volume(ubi_num, vol_id, mode);
...
}
struct ubi_volume_desc *ubi_open_volume(int ubi_num, int vol_id, int mode)
{
...
/*
* First of all, we have to get the UBI device to prevent its removal.
*/
ubi = ubi_get_device(ubi_num);
...
desc = kmalloc(sizeof(struct ubi_volume_desc), GFP_KERNEL);
...
spin_lock(&ubi->volumes_lock);
vol = ubi->volumes[vol_id]; /* (3) */
...
spin_unlock(&ubi->volumes_lock);
desc->vol = vol;
...
return desc;
}
struct ubi_device *ubi_get_device(int ubi_num)
{
struct ubi_device *ubi;
...
ubi = ubi_devices[ubi_num]; /* ubi_devices[] 在前一问题代码分析中的 ubi_attach_mtd_dev() 构建 */
...
return ubi;
}
static struct ubifs_info *alloc_ubifs_info(struct ubi_volume_desc *ubi)
{
struct ubifs_info *c;
c = kzalloc(sizeof(struct ubifs_info), GFP_KERNEL);
if (c) {
...
ubi_get_volume_info(ubi, &c->vi);
...
}
}
void ubi_get_volume_info(struct ubi_volume_desc *desc,
struct ubi_volume_info *vi)
{
ubi_do_get_volume_info(desc->vol->ubi, desc->vol, vi);
}
void ubi_do_get_volume_info(struct ubi_device *ubi, struct ubi_volume *vol,
struct ubi_volume_info *vi)
{
...
vi->usable_leb_size = vol->usable_leb_size;
...
}
static int ubifs_fill_super(struct super_block *sb, void *data, int silent)
{
...
err = mount_ubifs(c);
...
}
static int mount_ubifs(struct ubifs_info *c)
{
...
err = init_constants_early(c);
...
err = ubifs_read_superblock(c);
...
}
static int init_constants_early(struct ubifs_info *c)
{
...
c->leb_size = c->vi.usable_leb_size;
...
}
int ubifs_read_superblock(struct ubifs_info *c)
{
...
struct ubifs_sb_node *sup;
...
sup = ubifs_read_sb_node(c); /* 从写入到设备的 rootfs 镜像读取 superblock 信息 */
...
err = validate_sb(c, sup); /* 验证 rootfs 构建的 superblock 的合法性 */
...
}
static int validate_sb(struct ubifs_info *c, struct ubifs_sb_node *sup)
{
...
if (le32_to_cpu(sup->leb_size) != c->leb_size) { /* (4) 内核报错日志 */
ubifs_err(c, "LEB size mismatch: %d in superblock, %d real",
le32_to_cpu(sup->leb_size), c->leb_size);
goto failed;
}
...
failed:
ubifs_err(c, "bad superblock, error %d", err);
ubifs_dump_node(c, sup);
return -EINVAL;
}这个路径虽然很长，但并不复杂，在代码流程最后 validate_sb() 函数中的 (4) 处，内核报错。和前面的问题类似，又是一个 rootfs 镜像 rootfs.ubi 的参数 和 硬件参数 不匹配的问题，即 buildroot 中对应参数的配置问题。从前面的 open_ubi() 和 alloc_ubifs_info() 代码流程分析得知，参数 c->leb_size 反应 NAND 硬件参数，而 sup->leb_size 参数值来自 rootfs.ubi 。从 buildroot 的 fs/ubifs/ubifs.mk 的片段：
# -e 参数指定 LEB(Logical Erase Block) 的大小
UBIFS_OPTS := -e $(BR2_TARGET_ROOTFS_UBIFS_LEBSIZE) -c $(BR2_TARGET_ROOTFS_UBIFS_MAXLEBCNT) -m $(BR2_TARGET_ROOTFS_UBIFS_MINIOSIZE)
...
define ROOTFS_UBIFS_CMD
$(HOST_DIR)/usr/sbin/mkfs.ubifs -d $(TARGET_DIR) $(UBIFS_OPTS) -o $@
endef我们得知，配置项 BR2_TARGET_ROOTFS_UBIFS_LEBSIZE 修改 LEB(Logical Erase Block) 值，按日志提示：
[ 2.965365] UBIFS error (ubi0:0 pid 1): ubifs_read_superblock: LEB size mismatch: 129024 in superblock, 126976 real该值应该由 129024(0x1f800) 修改为 126976(0x1f000)：
重新编译，烧录运行，终于可以进入登录提示处了：
[ 2.162228] ubi0: attaching mtd9
[ 2.817396] ubi0: scanning is finished
[ 2.841103] ubi0: volume 0 ("rootfs") re-sized from 83 to 1668 LEBs
[ 2.848156] ubi0: attached mtd9 (name "NAND.rootfs", size 214 MiB)
[ 2.854435] ubi0: PEB size: 131072 bytes (128 KiB), LEB size: 126976 bytes
[ 2.861339] ubi0: min./max. I/O unit sizes: 2048/2048, sub-page size 512
[ 2.868081] ubi0: VID header offset: 2048 (aligned 2048), data offset: 4096
[ 2.875082] ubi0: good PEBs: 1711, bad PEBs: 1, corrupted PEBs: 0
[ 2.881199] ubi0: user volume: 1, internal volumes: 1, max. volumes count: 128
[ 2.888463] ubi0: max/mean erase counter: 1/0, WL threshold: 4096, image sequence number: 1890895802
[ 2.897644] ubi0: available PEBs: 0, total reserved PEBs: 1711, PEBs reserved for bad PEB handling: 39
[ 2.907010] ubi0: background thread "ubi_bgt0d" started, PID 65
......
[ 2.972922] UBIFS (ubi0:0): background thread "ubifs_bgt0_0" started, PID 66
[ 3.083296] UBIFS (ubi0:0): UBIFS: mounted UBI device 0, volume 0, name "rootfs"
[ 3.090747] UBIFS (ubi0:0): LEB size: 126976 bytes (124 KiB), min./max. I/O unit sizes: 2048 bytes/2048 bytes
[ 3.122798] UBIFS (ubi0:0): FS size: 210399232 bytes (200 MiB, 1657 LEBs), journal size 9023488 bytes (8 MiB, 72 LEBs)
[ 3.142800] UBIFS (ubi0:0): reserved for root: 0 bytes (0 KiB)
[ 3.148663] UBIFS (ubi0:0): media format: w4/r0 (latest is w5/r0), UUID 7A19D54A-3848-4AFB-8DDF-4E4A6B04D4FC, small LPT model
[ 3.184943] VFS: Mounted root (ubifs filesystem) on device 0:14.
[ 3.192113] devtmpfs: mounted
...
Welcome
(none) login: 虽然仍然还存在问题，但这和本文主题无关，就不在这里展开了。
4. 参考资料
[1] https://bootlin.com/blog/creating-flashing-ubi-ubifs-images/
[2] UBI FAQ and HOWTO
[3] UBI - Unsorted Block Images
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