Folks here is a patch i've made for qemu that adds a memory based block device, it utilizes memory on the Host side to emulate a block device.
I've tested this on a few boxes to allow a kernel/initramfs system to boot without needing a specified block device(it automatically creates a small one) and for installing a usable system on. One note you can never shut down the running system, but seems to work fine when only re-boots are required. I've installed debian on it a few times. Some Things I'd like comments on: - The auto-detection code in the block code causes the code to allocate the memory used twice, even though it only gets used the second time. - using qemu_mallocz seems to pre-allocate all the memory used, which is fine, but my early code with calloc only allocated what blocks were actually used. Does this bother people. Evan Felix diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/block.c kvm-28/qemu/block.c --- kvm-28/qemu.orig/block.c 2007-06-07 08:13:47.000000000 -0700 +++ kvm-28/qemu/block.c 2007-07-11 13:29:02.000000000 -0700 @@ -1244,6 +1244,7 @@ static int bdrv_write_em(BlockDriverStat void bdrv_init(void) { bdrv_register(&bdrv_raw); + bdrv_register(&bdrv_mem); bdrv_register(&bdrv_host_device); #ifndef _WIN32 bdrv_register(&bdrv_cow); diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/block-mem.c kvm-28/qemu/block-mem.c --- kvm-28/qemu.orig/block-mem.c 1969-12-31 16:00:00.000000000 -0800 +++ kvm-28/qemu/block-mem.c 2007-07-09 13:46:39.000000000 -0700 @@ -0,0 +1,129 @@ +/* + * Block Driver for a Memory disk on the host side. + * + * Copyright (c) 2007 Pacific Northwest National Laboratory + * and Evan Felix <[EMAIL PROTECTED]> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program (see the file COPYING included with this + * distribution); if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include "vl.h" +#include "block_int.h" + +//I took this from block-raw.c +#ifdef __sun__ +#define _POSIX_PTHREAD_SEMANTICS 1 +#include <signal.h> +#include <sys/dkio.h> +#endif +#ifdef __linux__ +#include <sys/ioctl.h> +#include <linux/cdrom.h> +#include <linux/fd.h> +#endif +#ifdef __FreeBSD__ +#include <sys/disk.h> +#endif + +#define DEBUG_MEM 0 + +#ifdef DEBUG_MEM +#define DEBUG(fmt,a...) printf("D:%s:%d> " fmt "\n",__FILE__,__LINE__,##a) +#else +#define DEBUG(fmt,a...) +#endif + +typedef struct BDRVMemState { + void *memory; + int64_t length; +} BDRVMemState; + +static int mem_open(BlockDriverState *bs, const char *filename, int flags) +{ + BDRVMemState *s = bs->opaque; + + bs->locked = 1; + bs->type = BDRV_TYPE_HD; + //Try to parse the filename as a number of bytes. add recognize M,K,G laterz. + s->length = strtol(filename+4,NULL,0); + DEBUG("mem_open:Raw Image size: %s -> %ld\n",filename,s->length); + + s->memory=qemu_mallocz(s->length); + if (! s->memory) + return -ENOMEM; + return 0; +} + +static void mem_close(BlockDriverState *bs) { + + BDRVMemState *s = bs->opaque; + DEBUG("mem_close: %lld\n",s->length); + qemu_free(s->memory); + s->length=0; +} + +static int mem_pread(BlockDriverState *bs, int64_t offset, + uint8_t *buf, int count) +{ + BDRVMemState *s = bs->opaque; + + if (offset < 0 || (offset + count)>s->length) { + return -EINVAL; + } + + memcpy(buf,(s->memory+offset),count); + return count; +} + +static int mem_pwrite(BlockDriverState *bs, int64_t offset, + const uint8_t *buf, int count) +{ + BDRVMemState *s = bs->opaque; + + if (offset < 0 || (offset + count)>s->length) { + return -EINVAL; + } + + memcpy((s->memory+offset),buf,count); + return count; +} + +static void mem_flush(BlockDriverState *bs) +{ + //Do Nothing for now + DEBUG("mem_flush\n"); +} + +static int64_t mem_getlength(BlockDriverState *bs) +{ + BDRVMemState *s = bs->opaque; + + return s->length; +} + +BlockDriver bdrv_mem = { + .format_name = "mem", + .instance_size = sizeof(BDRVMemState), + .protocol_name = "mem", + + .bdrv_open = mem_open, + .bdrv_close = mem_close, + .bdrv_flush = mem_flush, + + .bdrv_pread = mem_pread, + .bdrv_pwrite = mem_pwrite, + .bdrv_getlength = mem_getlength, +}; diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/hw/pc.c kvm-28/qemu/hw/pc.c --- kvm-28/qemu.orig/hw/pc.c 2007-06-07 08:13:47.000000000 -0700 +++ kvm-28/qemu/hw/pc.c 2007-07-06 16:48:12.000000000 -0700 @@ -583,8 +583,13 @@ static void pc_init1(int ram_size, int v uint8_t old_bootsect[512]; if (bs_table[0] == NULL) { - fprintf(stderr, "A disk image must be given for 'hda' when booting a Linux kernel\n"); - exit(1); + fprintf(stderr, "A disk image must be given when booting a Linux kernel....\n\tCreating Simple memory backed Disk\n"); + bs_table[i] = bdrv_new("hda"); + if (bdrv_open(bs_table[0], "mem:4096", 0) < 0) { + fprintf(stderr, "qemu: could not open hard disk image '%s'\n", + "mem:512"); + exit(1); + } } snprintf(buf, sizeof(buf), "%s/%s", bios_dir, LINUX_BOOT_FILENAME); ret = load_image(buf, bootsect); diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/Makefile kvm-28/qemu/Makefile --- kvm-28/qemu.orig/Makefile 2007-06-07 08:13:47.000000000 -0700 +++ kvm-28/qemu/Makefile 2007-07-06 14:24:44.000000000 -0700 @@ -39,7 +39,7 @@ subdir-%: dyngen$(EXESUF) recurse-all: $(patsubst %,subdir-%, $(TARGET_DIRS)) -qemu-img$(EXESUF): qemu-img.c cutils.c block.c block-raw.c block-cow.c block-qcow.c aes.c block-vmdk.c block-cloop.c block-dmg.c block-bochs.c block-vpc.c block-vvfat.c block-qcow2.c +qemu-img$(EXESUF): qemu-img.c cutils.c block.c block-raw.c block-cow.c block-qcow.c aes.c block-vmdk.c block-cloop.c block-dmg.c block-bochs.c block-vpc.c block-vvfat.c block-qcow2.c block-mem.c $(CC) -DQEMU_TOOL $(CFLAGS) $(CPPFLAGS) $(BASE_CFLAGS) $(LDFLAGS) $(BASE_LDFLAGS) -o $@ $^ -lz $(LIBS) dyngen$(EXESUF): dyngen.c diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/Makefile.target kvm-28/qemu/Makefile.target --- kvm-28/qemu.orig/Makefile.target 2007-06-07 08:13:47.000000000 -0700 +++ kvm-28/qemu/Makefile.target 2007-07-06 13:43:31.000000000 -0700 @@ -326,7 +326,7 @@ endif VL_OBJS=vl.o osdep.o readline.o monitor.o pci.o console.o loader.o isa_mmio.o VL_OBJS+=cutils.o migration.o VL_OBJS+=block.o block-raw.o -VL_OBJS+=block-cow.o block-qcow.o aes.o block-vmdk.o block-cloop.o block-dmg.o block-bochs.o block-vpc.o block-vvfat.o block-qcow2.o +VL_OBJS+=block-cow.o block-qcow.o aes.o block-vmdk.o block-cloop.o block-dmg.o block-bochs.o block-vpc.o block-vvfat.o block-qcow2.o block-mem.o ifdef CONFIG_WIN32 VL_OBJS+=tap-win32.o endif diff -urNp -x '*~' -x '*html' -x '*.mak' -x '*.1' kvm-28/qemu.orig/vl.h kvm-28/qemu/vl.h --- kvm-28/qemu.orig/vl.h 2007-06-07 08:13:47.000000000 -0700 +++ kvm-28/qemu/vl.h 2007-07-06 14:23:50.000000000 -0700 @@ -561,6 +561,7 @@ typedef struct BlockDriverState BlockDri typedef struct BlockDriver BlockDriver; extern BlockDriver bdrv_raw; +extern BlockDriver bdrv_mem; extern BlockDriver bdrv_host_device; extern BlockDriver bdrv_cow; extern BlockDriver bdrv_qcow;