android rootfs的挂载流程[通俗易懂]

int boot_ramdisk_high(struct lmb *lmb, ulong rd_data, ulong rd_len,
ulong *initrd_start, ulong *initrd_end)
{
char    *s;
ulong   initrd_high;
int initrd_copy_to_ram = 1;
if ((s = getenv("initrd_high")) != NULL) {
/* a value of "no" or a similar string will act like 0, * turning the "load high" feature off. This is intentional. */
initrd_high = simple_strtoul(s, NULL, 16);
if (initrd_high == ~0)
initrd_copy_to_ram = 0;
} else {
initrd_high = getenv_bootm_mapsize() + getenv_bootm_low();
}
#ifdef CONFIG_LOGBUFFER
/* Prevent initrd from overwriting logbuffer */
lmb_reserve(lmb, logbuffer_base() - LOGBUFF_OVERHEAD, LOGBUFF_RESERVE);
#endif
debug("## initrd_high = 0x%08lx, copy_to_ram = %d\n",
initrd_high, initrd_copy_to_ram);
if (rd_data) {
if (!initrd_copy_to_ram) {  /* zero-copy ramdisk support */
debug(" in-place initrd\n");
*initrd_start = rd_data;
*initrd_end = rd_data + rd_len;
lmb_reserve(lmb, rd_data, rd_len);
} else {
if (initrd_high)
*initrd_start = (ulong)lmb_alloc_base(lmb,
rd_len, 0x1000, initrd_high);
else
*initrd_start = (ulong)lmb_alloc(lmb, rd_len,
0x1000);
if (*initrd_start == 0) {
puts("ramdisk - allocation error\n");
goto error;
}
bootstage_mark(BOOTSTAGE_ID_COPY_RAMDISK);
*initrd_end = *initrd_start + rd_len;
printf(" Loading Ramdisk to %08lx, end %08lx ... ",
*initrd_start, *initrd_end);
/*把ramdisk拷贝到指定的地址*/
memmove_wd((void *)*initrd_start,
(void *)rd_data, rd_len, CHUNKSZ);
#ifdef CONFIG_MP
/*
* Ensure the image is flushed to memory to handle
* AMP boot scenarios in which we might not be
* HW cache coherent
*/
flush_cache((unsigned long)*initrd_start, rd_len);
#endif
puts("OK\n");
}
} else {
*initrd_start = 0;
*initrd_end = 0;
}
debug(" ramdisk load start = 0x%08lx, ramdisk load end = 0x%08lx\n",
*initrd_start, *initrd_end);
return 0;
error:
return -1;
}

static void setup_initrd_tag(bd_t *bd, ulong initrd_start, ulong initrd_end)
{
/* an ATAG_INITRD node tells the kernel where the compressed * ramdisk can be found. ATAG_RDIMG is a better name, actually. */
params->hdr.tag = ATAG_INITRD2;
params->hdr.size = tag_size (tag_initrd);
params->u.initrd.start = initrd_start;
params->u.initrd.size = initrd_end - initrd_start;
params = tag_next (params);
}
static void boot_jump_linux(bootm_headers_t *images, int flag)
{
#ifdef CONFIG_ARM64
void (*kernel_entry)(void *fdt_addr, void *res0, void *res1,
void *res2);
int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
kernel_entry = (void (*)(void *fdt_addr, void *res0, void *res1,
void *res2))images->ep;
debug("## Transferring control to Linux (at address %lx)...\n",
(ulong) kernel_entry);
bootstage_mark(BOOTSTAGE_ID_RUN_OS);
announce_and_cleanup(fake);
if (!fake) {
do_nonsec_virt_switch();
kernel_entry(images->ft_addr, NULL, NULL, NULL);
}
#else
unsigned long machid = gd->bd->bi_arch_number;
char *s;
void (*kernel_entry)(int zero, int arch, uint params);
unsigned long r2;
int fake = (flag & BOOTM_STATE_OS_FAKE_GO);
kernel_entry = (void (*)(int, int, uint))images->ep;
s = getenv("machid");
if (s) {
if (strict_strtoul(s, 16, &machid) < 0) {
debug("strict_strtoul failed!\n");
return;
}
printf("Using machid 0x%lx from environment\n", machid);
}
debug("## Transferring control to Linux (at address %08lx)" \
"...\n", (ulong) kernel_entry);
bootstage_mark(BOOTSTAGE_ID_RUN_OS);
announce_and_cleanup(fake);
if (IMAGE_ENABLE_OF_LIBFDT && images->ft_len)
/*使用dtb*/
r2 = (unsigned long)images->ft_addr;
else
/*不使用dtb*/
r2 = gd->bd->bi_boot_params;
if (!fake) {
#ifdef CONFIG_ARMV7_NONSEC
if (armv7_boot_nonsec()) {
armv7_init_nonsec();
secure_ram_addr(_do_nonsec_entry)(kernel_entry,
0, machid, r2);
} else
#endif
/*启动内核时把tag的地址通过参数传入，内核可以通过该地址解析bootloader传入的tag，包括ramdisk的addr及size*/
kernel_entry(0, machid, r2);
}
#endif
}

int fdt_initrd(void *fdt, ulong initrd_start, ulong initrd_end)
{
int   nodeoffset;
int   err, j, total;
int is_u64;
uint64_t addr, size;
/* just return if the size of initrd is zero */
if (initrd_start == initrd_end)
return 0;
/* find or create "/chosen" node. */
nodeoffset = fdt_find_or_add_subnode(fdt, 0, "chosen");
if (nodeoffset < 0)
return nodeoffset;
total = fdt_num_mem_rsv(fdt);
/*
* Look for an existing entry and update it.  If we don't find
* the entry, we will j be the next available slot.
*/
for (j = 0; j < total; j++) {
err = fdt_get_mem_rsv(fdt, j, &addr, &size);
if (addr == initrd_start) {
fdt_del_mem_rsv(fdt, j);
break;
}
}
err = fdt_add_mem_rsv(fdt, initrd_start, initrd_end - initrd_start);
if (err < 0) {
printf("fdt_initrd: %s\n", fdt_strerror(err));
return err;
}
is_u64 = (fdt_address_cells(fdt, 0) == 2);
/*往dtb中添加一个"linux,initrd-start"属性，内核通过解析dtb可以获知ramdisk的地址*/
err = fdt_setprop_uxx(fdt, nodeoffset, "linux,initrd-start",
(uint64_t)initrd_start, is_u64);
if (err < 0) {
printf("WARNING: could not set linux,initrd-start %s.\n",
fdt_strerror(err));
return err;
}
/*往dtb中添加一个"linux,initrd-end"属性，内核通过解析dtb，结合"linux,initrd-start"可以获知dtb的size*/
err = fdt_setprop_uxx(fdt, nodeoffset, "linux,initrd-end",
(uint64_t)initrd_end, is_u64);
if (err < 0) {
printf("WARNING: could not set linux,initrd-end %s.\n",
fdt_strerror(err));
return err;
}
return 0;
}

static void __init early_init_dt_check_for_initrd(unsigned long node)
{
u64 start, end;
unsigned long len;
__be32 *prop;
pr_debug("Looking for initrd properties... ");
prop = of_get_flat_dt_prop(node, "linux,initrd-start", &len);//读取ramdisk在内存的起始地址
if (!prop)
return;
start = of_read_number(prop, len/4);
prop = of_get_flat_dt_prop(node, "linux,initrd-end", &len);//读取ramdisk在内存的结束地址
if (!prop)
return;
end = of_read_number(prop, len/4);
initrd_start = (unsigned long)__va(start);
initrd_end = (unsigned long)__va(end);
initrd_below_start_ok = 1;
printk("initrd_start=0x%llx initrd_end=0x%llx\n",
(unsigned long long)start, (unsigned long long)end);
}

void __init vfs_caches_init(unsigned long mempages)
{
unsigned long reserve;
/* Base hash sizes on available memory, with a reserve equal to 150% of current kernel size */
reserve = min((mempages - nr_free_pages()) * 3/2, mempages - 1);
mempages -= reserve;
names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
dcache_init();
inode_init();
files_init(mempages);
mnt_init();
bdev_cache_init();
chrdev_init();
}
void __init mnt_init(void)
{
unsigned u;
int err;
init_rwsem(&namespace_sem);
mnt_cache = kmem_cache_create("mnt_cache", sizeof(struct mount),
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
mount_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
mountpoint_hashtable = (struct list_head *)__get_free_page(GFP_ATOMIC);
if (!mount_hashtable || !mountpoint_hashtable)
panic("Failed to allocate mount hash table\n");
printk(KERN_INFO "Mount-cache hash table entries: %lu\n", HASH_SIZE);
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mount_hashtable[u]);
for (u = 0; u < HASH_SIZE; u++)
INIT_LIST_HEAD(&mountpoint_hashtable[u]);
br_lock_init(&vfsmount_lock);
err = sysfs_init();
if (err)
printk(KERN_WARNING "%s: sysfs_init error: %d\n",
__func__, err);
fs_kobj = kobject_create_and_add("fs", NULL);
if (!fs_kobj)
printk(KERN_WARNING "%s: kobj create error\n", __func__);
init_rootfs();
init_mount_tree();
}

static struct file_system_type rootfs_fs_type = {
.name       = "rootfs",
.mount      = rootfs_mount,
.kill_sb    = kill_litter_super,
};
int __init init_rootfs(void)
{
int err;
err = bdi_init(&ramfs_backing_dev_info);
if (err)
return err;
err = register_filesystem(&rootfs_fs_type);   //注册rootfs文件系统
if (err)
bdi_destroy(&ramfs_backing_dev_info);
return err;
}

static void __init init_mount_tree(void)
{
struct vfsmount *mnt;
struct mnt_namespace *ns;
struct path root;
struct file_system_type *type;
type = get_fs_type("rootfs");
if (!type)
panic("Can't find rootfs type");
mnt = vfs_kern_mount(type, 0, "rootfs", NULL);
put_filesystem(type);
if (IS_ERR(mnt))
panic("Can't create rootfs");
ns = create_mnt_ns(mnt);
if (IS_ERR(ns))
panic("Can't allocate initial namespace");
init_task.nsproxy->mnt_ns = ns;
get_mnt_ns(ns);
root.mnt = mnt;
root.dentry = mnt->mnt_root;
set_fs_pwd(current->fs, &root);
set_fs_root(current->fs, &root);
}
struct vfsmount *
vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void *data)
{
struct mount *mnt;
struct dentry *root;
if (!type)
return ERR_PTR(-ENODEV);
mnt = alloc_vfsmnt(name);
if (!mnt)
return ERR_PTR(-ENOMEM);
if (flags & MS_KERNMOUNT)
mnt->mnt.mnt_flags = MNT_INTERNAL;
root = mount_fs(type, flags, name, data);
if (IS_ERR(root)) {
free_vfsmnt(mnt);
return ERR_CAST(root);
}
mnt->mnt.mnt_root = root;
mnt->mnt.mnt_sb = root->d_sb;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
mnt->mnt_parent = mnt;
br_write_lock(&vfsmount_lock);
list_add_tail(&mnt->mnt_instance, &root->d_sb->s_mounts);
br_write_unlock(&vfsmount_lock);
return &mnt->mnt;
}
struct dentry *
mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
{
struct dentry *root;
struct super_block *sb;
char *secdata = NULL;
int error = -ENOMEM;
if (data && !(type->fs_flags & FS_BINARY_MOUNTDATA)) {
secdata = alloc_secdata();
if (!secdata)
goto out;
error = security_sb_copy_data(data, secdata);
if (error)
goto out_free_secdata;
}
root = type->mount(type, flags, name, data);
if (IS_ERR(root)) {
error = PTR_ERR(root);
goto out_free_secdata;
}
sb = root->d_sb;
BUG_ON(!sb);
WARN_ON(!sb->s_bdi);
WARN_ON(sb->s_bdi == &default_backing_dev_info);
sb->s_flags |= MS_BORN;
error = security_sb_kern_mount(sb, flags, secdata);
if (error)
goto out_sb;
/* * filesystems should never set s_maxbytes larger than MAX_LFS_FILESIZE * but s_maxbytes was an unsigned long long for many releases. Throw * this warning for a little while to try and catch filesystems that * violate this rule. */
WARN((sb->s_maxbytes < 0), "%s set sb->s_maxbytes to "
"negative value (%lld)\n", type->name, sb->s_maxbytes);
up_write(&sb->s_umount);
free_secdata(secdata);
return root;
out_sb:
dput(root);
deactivate_locked_super(sb);
out_free_secdata:
free_secdata(secdata);
out:
return ERR_PTR(error);
}

static struct dentry *rootfs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_nodev(fs_type, flags|MS_NOUSER, data, ramfs_fill_super);
}
struct dentry *mount_nodev(struct file_system_type *fs_type,
int flags, void *data,
int (*fill_super)(struct super_block *, void *, int))
{
int error;
struct super_block *s = sget(fs_type, NULL, set_anon_super, flags, NULL);
if (IS_ERR(s))
return ERR_CAST(s);
error = fill_super(s, data, flags & MS_SILENT ? 1 : 0);
if (error) {
deactivate_locked_super(s);
return ERR_PTR(error);
}
s->s_flags |= MS_ACTIVE;
return dget(s->s_root);
}

static int __init populate_rootfs(void)
{
char *err = unpack_to_rootfs(__initramfs_start, __initramfs_size);    //Android内核中没有initramfs，这个函数什么也不做
if (err)
panic(err); /* Failed to decompress INTERNAL initramfs */
if (initrd_start) {
#ifdef CONFIG_BLK_DEV_RAM
int fd;
printk(KERN_INFO "Trying to unpack rootfs image as initramfs...\n");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start);
if (!err) {
free_initrd();
goto done;
} else {
clean_rootfs();
unpack_to_rootfs(__initramfs_start, __initramfs_size);
}
printk(KERN_INFO "rootfs image is not initramfs (%s)"
"; looks like an initrd\n", err);
fd = sys_open("/initrd.image",
O_WRONLY|O_CREAT, 0700);
if (fd >= 0) {
sys_write(fd, (char *)initrd_start,
initrd_end - initrd_start);
sys_close(fd);
free_initrd();
}
done:
#else
printk(KERN_INFO "Unpacking initramfs...\n");
err = unpack_to_rootfs((char *)initrd_start,
initrd_end - initrd_start);
if (err)
printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err);
free_initrd();
#endif
/* * Try loading default modules from initramfs. This gives * us a chance to load before device_initcalls. */
load_default_modules();
}
return 0;
}
rootfs_initcall(populate_rootfs);

static char * __init unpack_to_rootfs(char *buf, unsigned len)
{
int written, res;
decompress_fn decompress;
const char *compress_name;
static __initdata char msg_buf[64];
header_buf = kmalloc(110, GFP_KERNEL);
symlink_buf = kmalloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1, GFP_KERNEL);
name_buf = kmalloc(N_ALIGN(PATH_MAX), GFP_KERNEL);
if (!header_buf || !symlink_buf || !name_buf)
panic("can't allocate buffers");
state = Start;
this_header = 0;
message = NULL;
while (!message && len) {
loff_t saved_offset = this_header;
if (*buf == '0' && !(this_header & 3)) {
state = Start;
written = write_buffer(buf, len);
buf += written;
len -= written;
continue;
}
if (!*buf) {
buf++;
len--;
this_header++;
continue;
}
this_header = 0;
decompress = decompress_method(buf, len, &compress_name);
if (decompress) {
res = decompress(buf, len, NULL, flush_buffer, NULL,
&my_inptr, error);
if (res)
error("decompressor failed");
} else if (compress_name) {
if (!message) {
snprintf(msg_buf, sizeof msg_buf,
"compression method %s not configured",
compress_name);
message = msg_buf;
}
} else
error("junk in compressed archive");
if (state != Reset)
error("junk in compressed archive");
this_header = saved_offset + my_inptr;
buf += my_inptr;
len -= my_inptr;
}
dir_utime();
kfree(name_buf);
kfree(symlink_buf);
kfree(header_buf);
return message;
}