Re: [PATCH] Memory Based Block Device

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Evan Felix wrote:
> 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 often use -hda /dev/null for -kernel/-append.

If you really want to implement a "proper" solution for -kernel/-append, 
I think the right thing to do would be to use an option ROM instead of a 
fake boot sector.

Regards,

Anthony Liguori

> 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 <e@pnl.gov>
> + *
> + *  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;
>
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>   


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