initramfs unpacker

[Alexander Viro]

	Aplogies for delay - there was more RL crap than I'd like...
Anyway, here's promised initramfs unpacking code.  The only exported
function below (unpack_to_rootfs(buf, len)) handles the format described
in v3 of your specification.  Basically, it's an FSM that understands
how to do (incremental) cpio -i and code feeding it with data - straight
from buffer or ugzipped.  No intermediate files, no nothing - we just
have inflate.c flush_window() feeding the next chunk into FSM.

	Now, whether we want to always hijack the mechainsm for passing
initrd images or use a separate section (or both, for that matter) is
a separate story.  In any case, init.c code should just call unpack_to_rootfs()
for the image in memory, no matter how it got there.  After VFS caches are
initialized, that is...

	BTW, AFAICS code will get simpler if we kill the alignment requirement
for cpio chunks.  Maybe it's worth doing...

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/slab.h>

static void __init error(char *x)
{
	panic("populate_root: %s\n", x);
}

static void __init *malloc(int size)
{
	return kmalloc(size, GFP_KERNEL);
}

static void __init free(void *where)
{
	kfree(where);
}

asmlinkage long sys_mkdir(char *name, int mode);
asmlinkage long sys_mknod(char *name, int mode, dev_t dev);
asmlinkage long sys_symlink(char *old, char *new);
asmlinkage long sys_link(char *old, char *new);
asmlinkage long sys_write(int fd, void *buf, ssize_t size);
asmlinkage long sys_chown(char *name, uid_t uid, gid_t gid);
asmlinkage long sys_lchown(char *name, uid_t uid, gid_t gid);
asmlinkage long sys_fchown(int fd, uid_t uid, gid_t gid);
asmlinkage long sys_chmod(char *name, mode_t mode);
asmlinkage long sys_fchmod(int fd, mode_t mode);

/* link hash */

static struct hash {
	int ino, minor, major;
	struct hash *next;
	char *name;
} *head[32];

static inline int hash(int major, int minor, int ino)
{
	unsigned long tmp = ino + minor + (major << 3);
	tmp += tmp >> 5;
	return tmp & 31;
}

static char __init *find_link(int major, int minor, int ino, char *name)
{
	struct hash **p, *q;
	for (p = head + hash(major, minor, ino); *p; p = &(*p)->next) {
		if ((*p)->ino != ino)
			continue;
		if ((*p)->minor != minor)
			continue;
		if ((*p)->major != major)
			continue;
		return (*p)->name;
	}
	q = (struct hash *)malloc(sizeof(struct hash));
	if (!q)
		error("can't allocate link hash entry");
	q->ino = ino;
	q->minor = minor;
	q->major = major;
	q->name = name;
	q->next = NULL;
	*p = q;
	return NULL;
}

static void __init free_hash(void)
{
	struct hash **p, *q;
	for (p = head; p < head + 32; p++) {
		while (*p) {
			q = *p;
			*p = q->next;
			free(q);
		}
	}
}

/* cpio header parsing */

static __initdata unsigned long ino, major, minor, nlink;
static __initdata mode_t mode;
static __initdata unsigned long body_len, name_len;
static __initdata uid_t uid;
static __initdata gid_t gid;
static __initdata dev_t rdev;

static void __init parse_header(char *s)
{
	unsigned long parsed[12];
	char buf[9];
	int i;

	buf[8] = '\0';
	for (i = 0, s += 6; i < 12; i++, s += 8) {
		memcpy(buf, s, 8);
		parsed[i] = simple_strtoul(buf, NULL, 16);
	}
	ino = parsed[0];
	mode = parsed[1];
	uid = parsed[2];
	gid = parsed[3];
	nlink = parsed[4];
	body_len = parsed[6];
	major = parsed[7];
	minor = parsed[8];
	rdev = MKDEV(parsed[9], parsed[10]);
	name_len = parsed[11];
}

/* FSM */

enum state {
	Start,
	Collect,
	GotHeader,
	SkipIt,
	GotName,
	CopyFile,
	GotSymlink,
	Reset
} state, next_state;

char *victim;
unsigned count;
loff_t this_header, next_header;

static inline void eat(unsigned n)
{
	victim += n;
	this_header += n;
	count -= n;
}

#define N_ALIGN(len) ((((len) + 1) & ~3) + 2)

static __initdata char *collected;
static __initdata int remains;
static __initdata char *collect;

static void __init read_into(char *buf, unsigned size, enum state next)
{
	if (count >= size) {
		collected = victim;
		eat(size);
		state = next;
	} else {
		collect = collected = buf;
		remains = size;
		next_state = next;
		state = Collect;
	}
}

static __initdata char *header_buf, *symlink_buf, *name_buf;

static int __init do_start(void)
{
	read_into(header_buf, 110, GotHeader);
	return 0;
}

static int __init do_collect(void)
{
	unsigned n = remains;
	if (count < n)
		n = count;
	memcpy(collect, victim, n);
	eat(n);
	collect += n;
	if (remains -= n)
		return 1;
	state = next_state;
	return 0;
}

static int __init do_header(void)
{
	parse_header(collected);
	next_header = this_header + N_ALIGN(name_len) + body_len;
	next_header = (next_header + 3) & ~3;
	if (name_len <= 0 || name_len > PATH_MAX)
		state = SkipIt;
	else if (S_ISLNK(mode)) {
		if (body_len > PATH_MAX)
			state = SkipIt;
		else {
			collect = collected = symlink_buf;
			remains = N_ALIGN(name_len) + body_len;
			next_state = GotSymlink;
			state = Collect;
		}
	} else if (body_len && !S_ISREG(mode))
		state = SkipIt;
	else
		read_into(name_buf, N_ALIGN(name_len), GotName);
	return 0;
}

static int __init do_skip(void)
{
	if (this_header + count <= next_header) {
		eat(count);
		return 1;
	} else {
		eat(next_header - this_header);
		state = next_state;
		return 0;
	}
}

static int __init do_reset(void)
{
	while(count && *victim == '\0')
		eat(1);
	if (count && (this_header & 3))
		error("broken padding");
	return 1;
}

static int __init maybe_link(void)
{
	if (nlink >= 2) {
		char *old = find_link(major, minor, ino, collected);
		if (old)
			return (sys_link(old, collected) < 0) ? -1 : 1;
	}
	return 0;
}

static __initdata int wfd;

static int __init do_name(void)
{
	state = SkipIt;
	next_state = Start;
	if (strcmp(collected, "TRAILER!!!") == 0) {
		free_hash();
		next_state = Reset;
		return 0;
	}
	printk(KERN_INFO "-> %s\n", collected);
	if (S_ISREG(mode)) {
		if (maybe_link() >= 0) {
			wfd = sys_open(collected, O_WRONLY|O_CREAT, mode);
			if (wfd >= 0) {
				sys_fchown(wfd, uid, gid);
				sys_fchmod(wfd, mode);
				state = CopyFile;
			}
		}
	} else if (S_ISDIR(mode)) {
		sys_mkdir(collected, mode);
		sys_chown(collected, uid, gid);
	} else if (S_ISBLK(mode) || S_ISCHR(mode) ||
		   S_ISFIFO(mode) || S_ISSOCK(mode)) {
		if (maybe_link() == 0) {
			sys_mknod(collected, mode, rdev);
			sys_chown(collected, uid, gid);
		}
	} else
		panic("populate_root: bogus mode: %o\n", mode);
	return 0;
}

static int __init do_copy(void)
{
	if (count >= body_len) {
		sys_write(wfd, victim, body_len);
		sys_close(wfd);
		eat(body_len);
		state = SkipIt;
		return 0;
	} else {
		sys_write(wfd, victim, count);
		body_len -= count;
		eat(count);
		return 1;
	}
}

static int __init do_symlink(void)
{
	collected[N_ALIGN(name_len) + body_len] = '\0';
	sys_symlink(collected + N_ALIGN(name_len), collected);
	sys_lchown(collected, uid, gid);
	state = SkipIt;
	next_state = Start;
	return 0;
}

static __initdata int (*actions[])(void) = {
	[Start]		do_start,
	[Collect]	do_collect,
	[GotHeader]	do_header,
	[SkipIt]	do_skip,
	[GotName]	do_name,
	[CopyFile]	do_copy,
	[GotSymlink]	do_symlink,
	[Reset]		do_reset,
};

static int __init write_buffer(char *buf, unsigned len)
{
	count = len;
	victim = buf;

	while (!actions[state]())
		;
	return len - count;
}

static void __init flush_buffer(char *buf, unsigned len)
{
	int written;
	while ((written = write_buffer(buf, len)) < len) {
		char c = buf[written];
		if (c == '0') {
			buf += written;
			len -= written;
			state = Start;
			continue;
		} else
			error("junk in compressed archive");
	}
}

/*
 * gzip declarations
 */

#define OF(args)  args

#ifndef memzero
#define memzero(s, n)     memset ((s), 0, (n))
#endif

typedef unsigned char  uch;
typedef unsigned short ush;
typedef unsigned long  ulg;

#define WSIZE 0x8000    /* window size--must be a power of two, and */
			/*  at least 32K for zip's deflate method */

static uch *inbuf;
static uch *window;

static unsigned insize;  /* valid bytes in inbuf */
static unsigned inptr;   /* index of next byte to be processed in inbuf */
static unsigned outcnt;  /* bytes in output buffer */
static long bytes_out;

#define get_byte()  (inptr < insize ? inbuf[inptr++] : -1)
		
/* Diagnostic functions (stubbed out) */
#define Assert(cond,msg)
#define Trace(x)
#define Tracev(x)
#define Tracevv(x)
#define Tracec(c,x)
#define Tracecv(c,x)

#define STATIC static

static void flush_window(void);
static void error(char *m);
static void gzip_mark(void **);
static void gzip_release(void **);

#include "../lib/inflate.c"

static void __init gzip_mark(void **ptr)
{
}

static void __init gzip_release(void **ptr)
{
}

/* ===========================================================================
 * Write the output window window[0..outcnt-1] and update crc and bytes_out.
 * (Used for the decompressed data only.)
 */
static void __init flush_window(void)
{
	ulg c = crc;         /* temporary variable */
	unsigned n;
	uch *in, ch;

	flush_buffer(window, outcnt);
	in = window;
	for (n = 0; n < outcnt; n++) {
		ch = *in++;
		c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
	}
	crc = c;
	bytes_out += (ulg)outcnt;
	outcnt = 0;
}

void unpack_to_rootfs(char *buf, unsigned len)
{
	int written;
	header_buf = malloc(110);
	symlink_buf = malloc(PATH_MAX + N_ALIGN(PATH_MAX) + 1);
	name_buf = malloc(N_ALIGN(PATH_MAX));
	window = malloc(WSIZE);
	if (!window || !header_buf || !symlink_buf || !name_buf)
		error("can't allocate buffers");
	state = Start;
	this_header = 0;
	while (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;
		} else if (!*buf) {
			buf++;
			len--;
			this_header++;
			continue;
		}
		this_header = 0;
		insize = len;
		inbuf = buf;
		inptr = 0;
		outcnt = 0;		/* bytes in output buffer */
		bytes_out = 0;
		crc = (ulg)0xffffffffL; /* shift register contents */
		makecrc();
		if (gunzip())
			error("ungzip failed");
		if (state != Reset)
			error("junk in gzipped archive");
		this_header = saved_offset + inptr;
		buf += inptr;
		len -= inptr;
	}
	free(window);
	free(name_buf);
	free(symlink_buf);
	free(header_buf);
}