Re: [Qemu-devel] [patch] Remove requirement for -hda with -kernel

[Ross Kendall Axe <ross.axe@blueyonder.co.uk>]

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Fabrice Bellard wrote:
> 
> I like the idea, but your patch may not compile for win32. Maybe
> creating a generic "dummy:[size]" block device would be interesting
> instead ?
> 
> Fabrice.
> 

How about this?  With this patch you can specify e.g. '-hda dummy:256M'
to create a 256 Mb hard disc on the fly, backed by a file in the temp
directory which is deleted on exit.  This patch uses this general
mechanism to create the bogus 1-sector hard disc needed for booting a
Linux kernel.  This patch works on Linux and has been compile-tested on
Mingw.

Ross



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Index: Makefile
===================================================================
RCS file: /cvsroot/qemu/qemu/Makefile,v
retrieving revision 1.87
diff -u -p -r1.87 Makefile
--- Makefile	28 Apr 2005 21:15:08 -0000	1.87
+++ Makefile	29 Apr 2005 21:22:02 -0000
@@ -25,7 +25,7 @@ else
 endif
 endif
 
-qemu-img$(EXESUF): qemu-img.c block.c block-cow.c block-qcow.c aes.c block-vmdk.c block-cloop.c block-dmg.c block-bochs.c block-vpc.c block-vvfat.c
+qemu-img$(EXESUF): qemu-img.c block.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-dummy.c
 	$(CC) -DQEMU_TOOL $(CFLAGS) $(LDFLAGS) $(DEFINES) -o $@ $^ -lz $(LIBS)
 
 dyngen$(EXESUF): dyngen.c
Index: Makefile.target
===================================================================
RCS file: /cvsroot/qemu/qemu/Makefile.target,v
retrieving revision 1.69
diff -u -p -r1.69 Makefile.target
--- Makefile.target	28 Apr 2005 21:15:08 -0000	1.69
+++ Makefile.target	29 Apr 2005 21:22:03 -0000
@@ -314,7 +314,7 @@ endif
 
 # must use static linking to avoid leaving stuff in virtual address space
 VL_OBJS=vl.o osdep.o block.o readline.o monitor.o pci.o console.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
+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-dummy.o
 
 SOUND_HW = sb16.o
 AUDIODRV = audio.o noaudio.o wavaudio.o
Index: block.c
===================================================================
RCS file: /cvsroot/qemu/qemu/block.c,v
retrieving revision 1.22
diff -u -p -r1.22 block.c
--- block.c	28 Apr 2005 21:09:32 -0000	1.22
+++ block.c	29 Apr 2005 21:22:05 -0000
@@ -657,4 +657,5 @@ void bdrv_init(void)
     bdrv_register(&bdrv_bochs);
     bdrv_register(&bdrv_vpc);
     bdrv_register(&bdrv_vvfat);
+    bdrv_register(&bdrv_dummy);
 }
Index: vl.h
===================================================================
RCS file: /cvsroot/qemu/qemu/vl.h,v
retrieving revision 1.73
diff -u -p -r1.73 vl.h
--- vl.h	28 Apr 2005 21:15:08 -0000	1.73
+++ vl.h	29 Apr 2005 21:22:08 -0000
@@ -385,6 +385,7 @@ extern BlockDriver bdrv_dmg;
 extern BlockDriver bdrv_bochs;
 extern BlockDriver bdrv_vpc;
 extern BlockDriver bdrv_vvfat;
+extern BlockDriver bdrv_dummy;
 
 void bdrv_init(void);
 BlockDriver *bdrv_find_format(const char *format_name);
Index: hw/pc.c
===================================================================
RCS file: /cvsroot/qemu/qemu/hw/pc.c,v
retrieving revision 1.35
diff -u -p -r1.35 pc.c
--- hw/pc.c	15 Jan 2005 12:02:56 -0000	1.35
+++ hw/pc.c	29 Apr 2005 21:22:08 -0000
@@ -446,8 +446,14 @@ void pc_init(int ram_size, int vga_ram_s
         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, "qemu: Disk image not given for 'hda' when booting"
+                    " a Linux kernel; inventing one\n");
+            bs_table[0] = bdrv_new("hda");
+            if (bdrv_open(bs_table[0], "dummy:512", 0) < 0) {
+                fprintf(stderr, "qemu: could not create temporary diskimage\n");
+                exit(1);
+            }
+            boot_device = 'c';
         }
         snprintf(buf, sizeof(buf), "%s/%s", bios_dir, LINUX_BOOT_FILENAME);
         ret = load_image(buf, bootsect);
--- /dev/null	2005-04-29 15:39:30.000000000 +0100
+++ block-dummy.c	2005-04-29 21:48:18.000000000 +0100
@@ -0,0 +1,148 @@
+/*
+ * QEMU dummy block device driver
+ *
+ * Copyright (C) 2005 Ross Kendall Axe <ross.axe@blueyonder.co.uk>
+ * Portions copyright (c) 2003 Fabrice Bellard
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "vl.h"
+#include "block_int.h"
+
+#define eprintf(...) fprintf(stderr, __VA_ARGS__)
+
+struct bdrv_dummy_state {
+    int fd;
+    char filename[PATH_MAX];
+};
+
+
+static int dummy_probe(const uint8_t *buf, int buf_size, const char *filename)
+{
+    return (0 == strncmp("dummy:", filename, 6)) ? 2 : 0;
+}
+
+static int dummy_open(BlockDriverState *bs, const char *filename)
+{
+    struct bdrv_dummy_state *s = bs->opaque;
+    off_t size;
+#ifdef WIN32
+    char tmpname[L_tmpnam];
+#else
+    char tmpname[] = "/tmp/qemu-dummy.XXXXXX";
+#endif
+    char *ptr;
+
+    size = strtoull(filename + 6, &ptr, 10);
+    if(ptr == (filename + 6)) {
+	eprintf("Size not given for dummy disc\n");
+	return -1;
+    }
+    switch(*ptr) {
+    case 't':
+    case 'T':
+	size *= 1024;
+    case 'g':
+    case 'G':
+	size *= 1024;
+    case 'm':
+    case 'M':
+	size *= 1024;
+    case 'k':
+    case 'K':
+	size *= 1024;
+    case 'b':
+    case 'B':
+    case '\0':
+	break;
+    default:
+	eprintf("Unknown multiplicative suffix '%s'\n", ptr);
+	return -1;
+    }	
+
+#ifdef WIN32
+    if(tmpnam(tmpname))
+	s->fd = open(tmpname, O_RDWR | O_BINARY | O_LARGEFILE);
+    else
+	s->fd = -1;
+#else
+    s->fd = mkstemp(tmpname);
+#endif
+    if(s->fd < 0) {
+	perror("Couldn't create dummy disc image");
+	return -1;
+    }
+    s->filename[0] = '\0';
+    strncat(s->filename, tmpname, sizeof s->filename);
+
+    if(0 > ftruncate(s->fd, size)) {
+	perror("Couldn't size dummy disc image");
+	close(s->fd);
+	unlink(s->filename);
+	return -1;
+    }
+    bs->total_sectors = size / 512;
+    return 0;
+}
+
+static int dummy_read(BlockDriverState *bs, int64_t sector_num, 
+		      uint8_t *buf, int nb_sectors)
+{
+    struct bdrv_dummy_state *s = bs->opaque;
+    int ret;
+    
+    lseek(s->fd, sector_num * 512, SEEK_SET);
+    ret = read(s->fd, buf, nb_sectors * 512);
+    if (ret != nb_sectors * 512) 
+        return -1;
+    return 0;
+}
+
+static int dummy_write(BlockDriverState *bs, int64_t sector_num, 
+		       const uint8_t *buf, int nb_sectors)
+{
+    struct bdrv_dummy_state *s = bs->opaque;
+    int ret;
+    
+    lseek(s->fd, sector_num * 512, SEEK_SET);
+    ret = write(s->fd, buf, nb_sectors * 512);
+    if (ret != nb_sectors * 512) 
+        return -1;
+    return 0;
+}
+
+static void dummy_close(BlockDriverState *bs)
+{
+    struct bdrv_dummy_state *s = bs->opaque;
+
+    close(s->fd);
+    unlink(s->filename);
+}
+
+BlockDriver bdrv_dummy = {
+    "dummy",
+    sizeof (struct bdrv_dummy_state),
+    dummy_probe,
+    dummy_open,
+    dummy_read,
+    dummy_write,
+    dummy_close,
+    NULL,
+};