The qemu -kernel option currently requires specifying a hard disk
image with -hda. Ostensibly at least one hard disk is needed for
qemu's boot loader to populate the partition table in its array of
boot sectors.
Passing -hda /dev/zero tricks qemu into booting, which demonstrates
that the requirement is unnecessary. Booting with no disk image is
needed to support diskless configurations where a remote NFS directory
is used as the root filesystem. In this scenario, the user invokes
qemu with -kernel and -initrd options, with a specially configured
initrd that NFS-mounts a filesystem on / before passing control to the
real init.
The attached patch permits using the -kernel option with no disk
images, and skips copying the partition table in this case.
--Ed
diff -BurN qemu-snapshot-2006-03-27_23.orig/hw/pc.c qemu-snapshot-2006-03-27_23/hw/pc.c
--- qemu-snapshot-2006-03-27_23.orig/hw/pc.c 2006-04-05 13:05:17.000000000 +0000
+++ qemu-snapshot-2006-03-27_23/hw/pc.c 2006-04-05 13:12:40.000000000 +0000
@@ -707,10 +707,6 @@
uint8_t bootsect[512];
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);
- }
snprintf(buf, sizeof(buf), "%s/%s", bios_dir, LINUX_BOOT_FILENAME);
ret = load_image(buf, bootsect);
if (ret != sizeof(bootsect)) {
@@ -719,12 +715,14 @@
exit(1);
}
- if (bdrv_read(bs_table[0], 0, old_bootsect, 1) >= 0) {
- /* copy the MSDOS partition table */
- memcpy(bootsect + 0x1be, old_bootsect + 0x1be, 0x40);
- }
+ if (bs_table[0]) {
+ if (bdrv_read(bs_table[0], 0, old_bootsect, 1) >= 0) {
+ /* copy the MSDOS partition table */
+ memcpy(bootsect + 0x1be, old_bootsect + 0x1be, 0x40);
+ }
- bdrv_set_boot_sector(bs_table[0], bootsect, sizeof(bootsect));
+ bdrv_set_boot_sector(bs_table[0], bootsect, sizeof(bootsect));
+ }
/* now we can load the kernel */
ret = load_kernel(kernel_filename,
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