Minimal initramfs support (based on Al Viro's work).

Makefile

@@ -209,7 +209,7 @@ init-y		:= init/
 drivers-y	:= drivers/ sound/
 net-y		:= net/
 libs-y		:= lib/
-core-y		:=
+core-y		:= usr/
 SUBDIRS		:=
 
 ifeq ($(filter $(noconfig_targets),$(MAKECMDGOALS)),)

arch/i386/Makefile

@@ -18,6 +18,7 @@
 
 LDFLAGS		:= -m elf_i386
 OBJCOPYFLAGS	:= -O binary -R .note -R .comment -S
+ARCHBLOBLFLAGS	:= -I binary -O elf32-i386 -B i386
 LDFLAGS_vmlinux := -e stext
 
 CFLAGS += -pipe

arch/i386/vmlinux.lds.S

@@ -77,6 +77,10 @@ SECTIONS
 	*(.initcall7.init)
   }
   __initcall_end = .;
+  . = ALIGN(4096);
+  __initramfs_start = .;
+  .init.ramfs : { *(.init.initramfs) }
+  __initramfs_end = .;
   . = ALIGN(32);
   __per_cpu_start = .;
   .data.percpu  : { *(.data.percpu) }

init/Makefile

@@ -2,7 +2,7 @@
 # Makefile for the linux kernel.
 #
 
-obj-y    := main.o version.o do_mounts.o
+obj-y    := main.o version.o do_mounts.o initramfs.o
 
 # files to be removed upon make clean
 clean-files := ../include/linux/compile.h

init/do_mounts.c

@@ -748,9 +748,7 @@ void prepare_namespace(void)
 		mount_initrd = 0;
 	real_root_dev = ROOT_DEV;
 #endif
-	sys_mkdir("/dev", 0700);
-	sys_mkdir("/root", 0700);
-	sys_mknod("/dev/console", S_IFCHR|0600, MKDEV(TTYAUX_MAJOR, 1));
+
 #ifdef CONFIG_DEVFS_FS
 	sys_mount("devfs", "/dev", "devfs", 0, NULL);
 	do_devfs = 1;

init/initramfs.c

+#define __KERNEL_SYSCALLS__
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/unistd.h>
+#include <linux/delay.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;
+}
+
+static void __init 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);
+}
+
+extern unsigned long __initramfs_start, __initramfs_end;
+
+void __init populate_rootfs(void)
+{
+	unpack_to_rootfs((void *) &__initramfs_start,
+			 &__initramfs_end - &__initramfs_start);
+}

init/main.c

@@ -72,6 +72,7 @@ extern void pidhash_init(void);
 extern void pte_chain_init(void);
 extern void radix_tree_init(void);
 extern void free_initmem(void);
+extern void populate_rootfs(void);
 
 #ifdef CONFIG_TC
 extern void tc_init(void);
@@ -433,6 +434,7 @@ asmlinkage void __init start_kernel(void)
 	vfs_caches_init(num_physpages);
 	radix_tree_init();
 	signals_init();
+	populate_rootfs();
 #ifdef CONFIG_PROC_FS
 	proc_root_init();
 #endif

usr/Makefile

+
+include arch/$(ARCH)/Makefile
+
+obj-y := initramfs_data.o
+
+host-progs := gen_init_cpio
+
+clean-files := initramfs_data.cpio.gz
+
+$(obj)/initramfs_data.o: $(obj)/initramfs_data.cpio.gz
+	$(OBJCOPY) $(ARCHBLOBLFLAGS) \
+		--rename-section .data=.init.initramfs \
+		$(obj)/initramfs_data.cpio.gz $(obj)/initramfs_data.o
+	$(STRIP) -s $(obj)/initramfs_data.o
+
+$(obj)/initramfs_data.cpio.gz: $(obj)/gen_init_cpio
+	( cd $(obj) ; ./gen_init_cpio | gzip -9c > initramfs_data.cpio.gz )
+

usr/gen_init_cpio.c

+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <string.h>
+#include <unistd.h>
+#include <time.h>
+
+static unsigned int offset;
+static unsigned int ino = 721;
+
+static void push_rest(const char *name)
+{
+	unsigned int name_len = strlen(name) + 1;
+	unsigned int tmp_ofs;
+
+	fputs(name, stdout);
+	putchar(0);
+	offset += name_len;
+
+	tmp_ofs = name_len + 110;
+	while (tmp_ofs & 3) {
+		putchar(0);
+		offset++;
+		tmp_ofs++;
+	}
+}
+
+static void push_hdr(const char *s)
+{
+	fputs(s, stdout);
+	offset += 110;
+}
+
+static void cpio_trailer(void)
+{
+	char s[256];
+	const char *name = "TRAILER!!!";
+
+	sprintf(s, "%s%08X%08X%08lX%08lX%08X%08lX"
+	       "%08X%08X%08X%08X%08X%08X%08X",
+		"070701",		/* magic */
+		0,			/* ino */
+		0,			/* mode */
+		(long) 0,		/* uid */
+		(long) 0,		/* gid */
+		1,			/* nlink */
+		(long) 0,		/* mtime */
+		0,			/* filesize */
+		0,			/* major */
+		0,			/* minor */
+		0,			/* rmajor */
+		0,			/* rminor */
+		strlen(name) + 1,	/* namesize */
+		0);			/* chksum */
+	push_hdr(s);
+	push_rest(name);
+
+	while (offset % 512) {
+		putchar(0);
+		offset++;
+	}
+}
+
+static void cpio_mkdir(const char *name, unsigned int mode,
+		       uid_t uid, gid_t gid)
+{
+	char s[256];
+	time_t mtime = time(NULL);
+
+	sprintf(s,"%s%08X%08X%08lX%08lX%08X%08lX"
+	       "%08X%08X%08X%08X%08X%08X%08X",
+		"070701",		/* magic */
+		ino++,			/* ino */
+		S_IFDIR | mode,		/* mode */
+		(long) uid,		/* uid */
+		(long) gid,		/* gid */
+		2,			/* nlink */
+		(long) mtime,		/* mtime */
+		0,			/* filesize */
+		3,			/* major */
+		1,			/* minor */
+		0,			/* rmajor */
+		0,			/* rminor */
+		strlen(name) + 1,	/* namesize */
+		0);			/* chksum */
+	push_hdr(s);
+	push_rest(name);
+}
+
+static void cpio_mknod(const char *name, unsigned int mode,
+		       uid_t uid, gid_t gid, int dev_type,
+		       unsigned int maj, unsigned int min)
+{
+	char s[256];
+	time_t mtime = time(NULL);
+
+	if (dev_type == 'b')
+		mode |= S_IFBLK;
+	else
+		mode |= S_IFCHR;
+
+	sprintf(s,"%s%08X%08X%08lX%08lX%08X%08lX"
+	       "%08X%08X%08X%08X%08X%08X%08X",
+		"070701",		/* magic */
+		ino++,			/* ino */
+		mode,			/* mode */
+		(long) uid,		/* uid */
+		(long) gid,		/* gid */
+		1,			/* nlink */
+		(long) mtime,		/* mtime */
+		0,			/* filesize */
+		3,			/* major */
+		1,			/* minor */
+		maj,			/* rmajor */
+		min,			/* rminor */
+		strlen(name) + 1,	/* namesize */
+		0);			/* chksum */
+	push_hdr(s);
+	push_rest(name);
+}
+
+int main (int argc, char *argv[])
+{
+	cpio_mkdir("/dev", 0700, 0, 0);
+	cpio_mknod("/dev/console", 0600, 0, 0, 'c', 5, 1);
+	cpio_mkdir("/root", 0700, 0, 0);
+	cpio_trailer();
+
+	exit(0);
+
+	/* silence compiler warnings */
+	return 0;
+	(void) argc;
+	(void) argv;
+}
+