Linux preempt-rt

Check our new training course

Real-Time Linux with PREEMPT_RT

Check our new training course
with Creative Commons CC-BY-SA
lecture and lab materials

Bootlin logo

Elixir Cross Referencer

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/ctype.h>
#include <linux/fd.h>
#include <linux/tty.h>
#include <linux/suspend.h>
#include <linux/root_dev.h>
#include <linux/security.h>
#include <linux/delay.h>
#include <linux/mount.h>
#include <linux/device.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/initrd.h>
#include <linux/async.h>
#include <linux/fs_struct.h>
#include <linux/slab.h>
#include <linux/ramfs.h>
#include <linux/shmem_fs.h>

#include <linux/nfs_fs.h>
#include <linux/nfs_fs_sb.h>
#include <linux/nfs_mount.h>
#include <linux/raid/detect.h>
#include <uapi/linux/mount.h>

#include "do_mounts.h"

int root_mountflags = MS_RDONLY | MS_SILENT;
static char * __initdata root_device_name;
static char __initdata saved_root_name[64];
static int root_wait;

dev_t ROOT_DEV;

static int __init load_ramdisk(char *str)
{
	pr_warn("ignoring the deprecated load_ramdisk= option\n");
	return 1;
}
__setup("load_ramdisk=", load_ramdisk);

static int __init readonly(char *str)
{
	if (*str)
		return 0;
	root_mountflags |= MS_RDONLY;
	return 1;
}

static int __init readwrite(char *str)
{
	if (*str)
		return 0;
	root_mountflags &= ~MS_RDONLY;
	return 1;
}

__setup("ro", readonly);
__setup("rw", readwrite);

#ifdef CONFIG_BLOCK
struct uuidcmp {
	const char *uuid;
	int len;
};

/**
 * match_dev_by_uuid - callback for finding a partition using its uuid
 * @dev:	device passed in by the caller
 * @data:	opaque pointer to the desired struct uuidcmp to match
 *
 * Returns 1 if the device matches, and 0 otherwise.
 */
static int match_dev_by_uuid(struct device *dev, const void *data)
{
	struct block_device *bdev = dev_to_bdev(dev);
	const struct uuidcmp *cmp = data;

	if (!bdev->bd_meta_info ||
	    strncasecmp(cmp->uuid, bdev->bd_meta_info->uuid, cmp->len))
		return 0;
	return 1;
}

/**
 * devt_from_partuuid - looks up the dev_t of a partition by its UUID
 * @uuid_str:	char array containing ascii UUID
 *
 * The function will return the first partition which contains a matching
 * UUID value in its partition_meta_info struct.  This does not search
 * by filesystem UUIDs.
 *
 * If @uuid_str is followed by a "/PARTNROFF=%d", then the number will be
 * extracted and used as an offset from the partition identified by the UUID.
 *
 * Returns the matching dev_t on success or 0 on failure.
 */
static dev_t devt_from_partuuid(const char *uuid_str)
{
	struct uuidcmp cmp;
	struct device *dev = NULL;
	dev_t devt = 0;
	int offset = 0;
	char *slash;

	cmp.uuid = uuid_str;

	slash = strchr(uuid_str, '/');
	/* Check for optional partition number offset attributes. */
	if (slash) {
		char c = 0;

		/* Explicitly fail on poor PARTUUID syntax. */
		if (sscanf(slash + 1, "PARTNROFF=%d%c", &offset, &c) != 1)
			goto clear_root_wait;
		cmp.len = slash - uuid_str;
	} else {
		cmp.len = strlen(uuid_str);
	}

	if (!cmp.len)
		goto clear_root_wait;

	dev = class_find_device(&block_class, NULL, &cmp, &match_dev_by_uuid);
	if (!dev)
		return 0;

	if (offset) {
		/*
		 * Attempt to find the requested partition by adding an offset
		 * to the partition number found by UUID.
		 */
		devt = part_devt(dev_to_disk(dev),
				 dev_to_bdev(dev)->bd_partno + offset);
	} else {
		devt = dev->devt;
	}

	put_device(dev);
	return devt;

clear_root_wait:
	pr_err("VFS: PARTUUID= is invalid.\n"
	       "Expected PARTUUID=<valid-uuid-id>[/PARTNROFF=%%d]\n");
	if (root_wait)
		pr_err("Disabling rootwait; root= is invalid.\n");
	root_wait = 0;
	return 0;
}

/**
 * match_dev_by_label - callback for finding a partition using its label
 * @dev:	device passed in by the caller
 * @data:	opaque pointer to the label to match
 *
 * Returns 1 if the device matches, and 0 otherwise.
 */
static int match_dev_by_label(struct device *dev, const void *data)
{
	struct block_device *bdev = dev_to_bdev(dev);
	const char *label = data;

	if (!bdev->bd_meta_info || strcmp(label, bdev->bd_meta_info->volname))
		return 0;
	return 1;
}

static dev_t devt_from_partlabel(const char *label)
{
	struct device *dev;
	dev_t devt = 0;

	dev = class_find_device(&block_class, NULL, label, &match_dev_by_label);
	if (dev) {
		devt = dev->devt;
		put_device(dev);
	}

	return devt;
}

static dev_t devt_from_devname(const char *name)
{
	dev_t devt = 0;
	int part;
	char s[32];
	char *p;

	if (strlen(name) > 31)
		return 0;
	strcpy(s, name);
	for (p = s; *p; p++) {
		if (*p == '/')
			*p = '!';
	}

	devt = blk_lookup_devt(s, 0);
	if (devt)
		return devt;

	/*
	 * Try non-existent, but valid partition, which may only exist after
	 * opening the device, like partitioned md devices.
	 */
	while (p > s && isdigit(p[-1]))
		p--;
	if (p == s || !*p || *p == '0')
		return 0;

	/* try disk name without <part number> */
	part = simple_strtoul(p, NULL, 10);
	*p = '\0';
	devt = blk_lookup_devt(s, part);
	if (devt)
		return devt;

	/* try disk name without p<part number> */
	if (p < s + 2 || !isdigit(p[-2]) || p[-1] != 'p')
		return 0;
	p[-1] = '\0';
	return blk_lookup_devt(s, part);
}
#endif /* CONFIG_BLOCK */

static dev_t devt_from_devnum(const char *name)
{
	unsigned maj, min, offset;
	dev_t devt = 0;
	char *p, dummy;

	if (sscanf(name, "%u:%u%c", &maj, &min, &dummy) == 2 ||
	    sscanf(name, "%u:%u:%u:%c", &maj, &min, &offset, &dummy) == 3) {
		devt = MKDEV(maj, min);
		if (maj != MAJOR(devt) || min != MINOR(devt))
			return 0;
	} else {
		devt = new_decode_dev(simple_strtoul(name, &p, 16));
		if (*p)
			return 0;
	}

	return devt;
}

/*
 *	Convert a name into device number.  We accept the following variants:
 *
 *	1) <hex_major><hex_minor> device number in hexadecimal represents itself
 *         no leading 0x, for example b302.
 *	2) /dev/nfs represents Root_NFS (0xff)
 *	3) /dev/<disk_name> represents the device number of disk
 *	4) /dev/<disk_name><decimal> represents the device number
 *         of partition - device number of disk plus the partition number
 *	5) /dev/<disk_name>p<decimal> - same as the above, that form is
 *	   used when disk name of partitioned disk ends on a digit.
 *	6) PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF representing the
 *	   unique id of a partition if the partition table provides it.
 *	   The UUID may be either an EFI/GPT UUID, or refer to an MSDOS
 *	   partition using the format SSSSSSSS-PP, where SSSSSSSS is a zero-
 *	   filled hex representation of the 32-bit "NT disk signature", and PP
 *	   is a zero-filled hex representation of the 1-based partition number.
 *	7) PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to
 *	   a partition with a known unique id.
 *	8) <major>:<minor> major and minor number of the device separated by
 *	   a colon.
 *	9) PARTLABEL=<name> with name being the GPT partition label.
 *	   MSDOS partitions do not support labels!
 *	10) /dev/cifs represents Root_CIFS (0xfe)
 *
 *	If name doesn't have fall into the categories above, we return (0,0).
 *	block_class is used to check if something is a disk name. If the disk
 *	name contains slashes, the device name has them replaced with
 *	bangs.
 */
dev_t name_to_dev_t(const char *name)
{
	if (strcmp(name, "/dev/nfs") == 0)
		return Root_NFS;
	if (strcmp(name, "/dev/cifs") == 0)
		return Root_CIFS;
	if (strcmp(name, "/dev/ram") == 0)
		return Root_RAM0;
#ifdef CONFIG_BLOCK
	if (strncmp(name, "PARTUUID=", 9) == 0)
		return devt_from_partuuid(name + 9);
	if (strncmp(name, "PARTLABEL=", 10) == 0)
		return devt_from_partlabel(name + 10);
	if (strncmp(name, "/dev/", 5) == 0)
		return devt_from_devname(name + 5);
#endif
	return devt_from_devnum(name);
}
EXPORT_SYMBOL_GPL(name_to_dev_t);

static int __init root_dev_setup(char *line)
{
	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;
	return 1;
}

__setup("rootwait", rootwait_setup);

static char * __initdata root_mount_data;
static int __init root_data_setup(char *str)
{
	root_mount_data = str;
	return 1;
}

static char * __initdata root_fs_names;
static int __init fs_names_setup(char *str)
{
	root_fs_names = str;
	return 1;
}

static unsigned int __initdata root_delay;
static int __init root_delay_setup(char *str)
{
	root_delay = simple_strtoul(str, NULL, 0);
	return 1;
}

__setup("rootflags=", root_data_setup);
__setup("rootfstype=", fs_names_setup);
__setup("rootdelay=", root_delay_setup);

/* This can return zero length strings. Caller should check */
static int __init split_fs_names(char *page, size_t size, char *names)
{
	int count = 1;
	char *p = page;

	strlcpy(p, root_fs_names, size);
	while (*p++) {
		if (p[-1] == ',') {
			p[-1] = '\0';
			count++;
		}
	}

	return count;
}

static int __init do_mount_root(const char *name, const char *fs,
				 const int flags, const void *data)
{
	struct super_block *s;
	struct page *p = NULL;
	char *data_page = NULL;
	int ret;

	if (data) {
		/* init_mount() requires a full page as fifth argument */
		p = alloc_page(GFP_KERNEL);
		if (!p)
			return -ENOMEM;
		data_page = page_address(p);
		/* zero-pad. init_mount() will make sure it's terminated */
		strncpy(data_page, data, PAGE_SIZE);
	}

	ret = init_mount(name, "/root", fs, flags, data_page);
	if (ret)
		goto out;

	init_chdir("/root");
	s = current->fs->pwd.dentry->d_sb;
	ROOT_DEV = s->s_dev;
	printk(KERN_INFO
	       "VFS: Mounted root (%s filesystem)%s on device %u:%u.\n",
	       s->s_type->name,
	       sb_rdonly(s) ? " readonly" : "",
	       MAJOR(ROOT_DEV), MINOR(ROOT_DEV));

out:
	if (p)
		put_page(p);
	return ret;
}

void __init mount_block_root(char *name, int flags)
{
	struct page *page = alloc_page(GFP_KERNEL);
	char *fs_names = page_address(page);
	char *p;
	char b[BDEVNAME_SIZE];
	int num_fs, i;

	scnprintf(b, BDEVNAME_SIZE, "unknown-block(%u,%u)",
		  MAJOR(ROOT_DEV), MINOR(ROOT_DEV));
	if (root_fs_names)
		num_fs = split_fs_names(fs_names, PAGE_SIZE, root_fs_names);
	else
		num_fs = list_bdev_fs_names(fs_names, PAGE_SIZE);
retry:
	for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1) {
		int err;

		if (!*p)
			continue;
		err = do_mount_root(name, p, flags, root_mount_data);
		switch (err) {
			case 0:
				goto out;
			case -EACCES:
			case -EINVAL:
				continue;
		}
	        /*
		 * Allow the user to distinguish between failed sys_open
		 * and bad superblock on root device.
		 * and give them a list of the available devices
		 */
		printk("VFS: Cannot open root device \"%s\" or %s: error %d\n",
				root_device_name, b, err);
		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");

		printk_all_partitions();
		panic("VFS: Unable to mount root fs on %s", b);
	}
	if (!(flags & SB_RDONLY)) {
		flags |= SB_RDONLY;
		goto retry;
	}

	printk("List of all partitions:\n");
	printk_all_partitions();
	printk("No filesystem could mount root, tried: ");
	for (i = 0, p = fs_names; i < num_fs; i++, p += strlen(p)+1)
		printk(" %s", p);
	printk("\n");
	panic("VFS: Unable to mount root fs on %s", b);
out:
	put_page(page);
}
 
#ifdef CONFIG_ROOT_NFS

#define NFSROOT_TIMEOUT_MIN	5
#define NFSROOT_TIMEOUT_MAX	30
#define NFSROOT_RETRY_MAX	5

static int __init mount_nfs_root(void)
{
	char *root_dev, *root_data;
	unsigned int timeout;
	int try, err;

	err = nfs_root_data(&root_dev, &root_data);
	if (err != 0)
		return 0;

	/*
	 * The server or network may not be ready, so try several
	 * times.  Stop after a few tries in case the client wants
	 * to fall back to other boot methods.
	 */
	timeout = NFSROOT_TIMEOUT_MIN;
	for (try = 1; ; try++) {
		err = do_mount_root(root_dev, "nfs",
					root_mountflags, root_data);
		if (err == 0)
			return 1;
		if (try > NFSROOT_RETRY_MAX)
			break;

		/* Wait, in case the server refused us immediately */
		ssleep(timeout);
		timeout <<= 1;
		if (timeout > NFSROOT_TIMEOUT_MAX)
			timeout = NFSROOT_TIMEOUT_MAX;
	}
	return 0;
}
#endif

#ifdef CONFIG_CIFS_ROOT

extern int cifs_root_data(char **dev, char **opts);

#define CIFSROOT_TIMEOUT_MIN	5
#define CIFSROOT_TIMEOUT_MAX	30
#define CIFSROOT_RETRY_MAX	5

static int __init mount_cifs_root(void)
{
	char *root_dev, *root_data;
	unsigned int timeout;
	int try, err;

	err = cifs_root_data(&root_dev, &root_data);
	if (err != 0)
		return 0;

	timeout = CIFSROOT_TIMEOUT_MIN;
	for (try = 1; ; try++) {
		err = do_mount_root(root_dev, "cifs", root_mountflags,
				    root_data);
		if (err == 0)
			return 1;
		if (try > CIFSROOT_RETRY_MAX)
			break;

		ssleep(timeout);
		timeout <<= 1;
		if (timeout > CIFSROOT_TIMEOUT_MAX)
			timeout = CIFSROOT_TIMEOUT_MAX;
	}
	return 0;
}
#endif

static bool __init fs_is_nodev(char *fstype)
{
	struct file_system_type *fs = get_fs_type(fstype);
	bool ret = false;

	if (fs) {
		ret = !(fs->fs_flags & FS_REQUIRES_DEV);
		put_filesystem(fs);
	}

	return ret;
}

static int __init mount_nodev_root(void)
{
	char *fs_names, *fstype;
	int err = -EINVAL;
	int num_fs, i;

	fs_names = (void *)__get_free_page(GFP_KERNEL);
	if (!fs_names)
		return -EINVAL;
	num_fs = split_fs_names(fs_names, PAGE_SIZE, root_fs_names);

	for (i = 0, fstype = fs_names; i < num_fs;
	     i++, fstype += strlen(fstype) + 1) {
		if (!*fstype)
			continue;
		if (!fs_is_nodev(fstype))
			continue;
		err = do_mount_root(root_device_name, fstype, root_mountflags,
				    root_mount_data);
		if (!err)
			break;
	}

	free_page((unsigned long)fs_names);
	return err;
}

void __init mount_root(void)
{
#ifdef CONFIG_ROOT_NFS
	if (ROOT_DEV == Root_NFS) {
		if (!mount_nfs_root())
			printk(KERN_ERR "VFS: Unable to mount root fs via NFS.\n");
		return;
	}
#endif
#ifdef CONFIG_CIFS_ROOT
	if (ROOT_DEV == Root_CIFS) {
		if (!mount_cifs_root())
			printk(KERN_ERR "VFS: Unable to mount root fs via SMB.\n");
		return;
	}
#endif
	if (ROOT_DEV == 0 && root_device_name && root_fs_names) {
		if (mount_nodev_root() == 0)
			return;
	}
#ifdef CONFIG_BLOCK
	{
		int err = create_dev("/dev/root", ROOT_DEV);

		if (err < 0)
			pr_emerg("Failed to create /dev/root: %d\n", err);
		mount_block_root("/dev/root", root_mountflags);
	}
#endif
}

/*
 * Prepare the namespace - decide what/where to mount, load ramdisks, etc.
 */
void __init prepare_namespace(void)
{
	if (root_delay) {
		printk(KERN_INFO "Waiting %d sec before mounting root device...\n",
		       root_delay);
		ssleep(root_delay);
	}

	/*
	 * wait for the known devices to complete their probing
	 *
	 * Note: this is a potential source of long boot delays.
	 * For example, it is not atypical to wait 5 seconds here
	 * for the touchpad of a laptop to initialize.
	 */
	wait_for_device_probe();

	md_run_setup();

	if (saved_root_name[0]) {
		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);
			goto out;
		}
		ROOT_DEV = name_to_dev_t(root_device_name);
		if (strncmp(root_device_name, "/dev/", 5) == 0)
			root_device_name += 5;
	}

	if (initrd_load())
		goto out;

	/* wait for any asynchronous scanning to complete */
	if ((ROOT_DEV == 0) && root_wait) {
		printk(KERN_INFO "Waiting for root device %s...\n",
			saved_root_name);
		while (driver_probe_done() != 0 ||
			(ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
			msleep(5);
		async_synchronize_full();
	}

	mount_root();
out:
	devtmpfs_mount();
	init_mount(".", "/", NULL, MS_MOVE, NULL);
	init_chroot(".");
}

static bool is_tmpfs;
static int rootfs_init_fs_context(struct fs_context *fc)
{
	if (IS_ENABLED(CONFIG_TMPFS) && is_tmpfs)
		return shmem_init_fs_context(fc);

	return ramfs_init_fs_context(fc);
}

struct file_system_type rootfs_fs_type = {
	.name		= "rootfs",
	.init_fs_context = rootfs_init_fs_context,
	.kill_sb	= kill_litter_super,
};

void __init init_rootfs(void)
{
	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
		(!root_fs_names || strstr(root_fs_names, "tmpfs")))
		is_tmpfs = true;
}