On Mon, Jun 14, 2010 at 07:12:38PM +0200, Grégoire Sutre wrote:
> On 06/14/2010 18:43, Colin Watson wrote:
>> Do you have any suggestions on how to deal with that? I'm not familiar
>> with multiboot and need guidance.
>
> A possible solution would be to use the multiboot-command line. AFAIK,
> the boot_device field of the multiboot information structure is supposed
> to pass this kind of partition information, but you cannot specify the
> partmaps in this field, hence its interpretation is ambiguous.
That would potentially allow a user to override things, but doesn't help
with users who don't change their configuration. Unless the user
explicitly configures things, boot_device is all we've got.
Thus, I guess we end up with a two-part fix:
1) Honour key=value pairs in the multiboot command line when booting
GRUB itself as a multiboot image. These would simply become
environment variables. Presumably this goes in grub_machine_init,
by analogy with kern/ieee1275/init.c. This allows users to
override the prefix on the command line as if they had changed the
image itself.
2) If multiboot_trampoline needs to change install_dos_part or
install_bsd_part based on the value of boot_device in the MBI, then
we know that the drive/partition part of prefix (which was
calculated in the same way as install_dos_part and install_bsd_part
when grub-setup was run) is now invalid and should be ignored.
This fact needs to be passed on to make_install_device.
Something like this? I'm afraid I have no idea how to test this (GRUB's
multiboot command doesn't seem to accept command-line arguments?), not
to mention that this is the first time I've been anywhere near most of
this code. I would greatly appreciate advice and review.
2010-06-15 Colin Watson <cjwat...@ubuntu.com>
Fix i386-pc prefix handling with nested partitions (Debian bug
#585068).
* include/grub/i386/pc/kernel.h (grub_multiboot_change_prefix): New
declaration.
* kern/i386/pc/startup.S (multiboot_entry): Save a pointer to the
MBI in startup_multiboot_info.
(multiboot_trampoline): If the new partition numbers differ from the
previous ones, then set grub_multiboot_change_prefix.
(grub_multiboot_change_prefix): New definition.
* kern/i386/pc/init.c (make_install_device): Invalidate any
drive/partition part of the prefix if grub_multiboot_change_prefix
is set. After that, if the prefix starts with "(,", fill the boot
drive in between those two characters, but expect that a full
partition specification including partition map names will follow.
(grub_parse_multiboot_cmdline): New function.
(grub_machine_init): If we have an MBI, copy it, then call
grub_parse_multiboot_cmdline.
* util/i386/pc/grub-setup.c (setup): Unless an explicit prefix was
specified, write a prefix without the drive name but including a
full partition specification.
=== modified file 'include/grub/i386/pc/kernel.h'
--- include/grub/i386/pc/kernel.h 2010-04-26 19:11:16 +0000
+++ include/grub/i386/pc/kernel.h 2010-06-15 11:02:34 +0000
@@ -44,6 +44,10 @@ extern grub_int32_t grub_install_bsd_par
/* The boot BIOS drive number. */
extern grub_uint8_t EXPORT_VAR(grub_boot_drive);
+/* Set if multiboot changed the partition numbers, so grub_prefix is now
+ invalid. */
+extern grub_uint8_t grub_multiboot_change_prefix;
+
#endif /* ! ASM_FILE */
#endif /* ! KERNEL_MACHINE_HEADER */
=== modified file 'kern/i386/pc/init.c'
--- kern/i386/pc/init.c 2010-05-21 18:08:48 +0000
+++ kern/i386/pc/init.c 2010-06-15 11:06:20 +0000
@@ -32,6 +32,7 @@
#include <grub/cache.h>
#include <grub/time.h>
#include <grub/cpu/tsc.h>
+#include <grub/multiboot.h>
struct mem_region
{
@@ -47,12 +48,29 @@ static int num_regions;
grub_addr_t grub_os_area_addr;
grub_size_t grub_os_area_size;
+/* A pointer to the MBI in its initial location. */
+struct multiboot_info *startup_multiboot_info = NULL;
+
+/* The MBI has to be copied to our BSS so that it won't be
+ overwritten. This is its final location. */
+static struct multiboot_info kern_multiboot_info;
+
static char *
make_install_device (void)
{
/* XXX: This should be enough. */
char dev[100], *ptr = dev;
+ if (grub_prefix[0] == '(' && grub_multiboot_change_prefix)
+ {
+ /* The multiboot information invalidated our hardcoded prefix because
+ partition numbers differed. Eliminate the drive/partition part of
+ the prefix, if possible. */
+ char *ket = grub_strchr (grub_prefix, ')');
+ if (ket)
+ grub_memmove (grub_prefix, ket + 1, grub_strlen (ket));
+ }
+
if (grub_prefix[0] != '(')
{
/* No hardcoded root partition - make it from the boot drive and the
@@ -83,6 +101,14 @@ make_install_device (void)
grub_snprintf (ptr, sizeof (dev) - (ptr - dev), ")%s", grub_prefix);
grub_strcpy (grub_prefix, dev);
}
+ else if (grub_prefix[1] == ',' || grub_prefix[1] == ')')
+ {
+ /* We have a prefix, but still need to fill in the boot drive. */
+ grub_snprintf (dev, sizeof (dev),
+ "(%cd%u%s", (grub_boot_drive & 0x80) ? 'h' : 'f',
+ grub_boot_drive & 0x7f, grub_prefix + 1);
+ grub_strcpy (grub_prefix, dev);
+ }
return grub_prefix;
}
@@ -134,6 +160,45 @@ compact_mem_regions (void)
}
}
+static void
+grub_parse_multiboot_cmdline (void)
+{
+ char *cmdline;
+ char *p;
+
+ if (! (kern_multiboot_info.flags & MULTIBOOT_INFO_CMDLINE))
+ return;
+
+ p = cmdline = grub_strdup ((char *) kern_multiboot_info.cmdline);
+
+ while (*p)
+ {
+ char *command = p;
+ char *end;
+ char *val;
+
+ end = grub_strchr (command, ' ');
+ if (end)
+ {
+ *end = '\0';
+ p = end + 1;
+ while (*p == ' ')
+ ++p;
+ }
+
+ /* Process command. */
+ val = grub_strchr (command, '=');
+ if (val)
+ {
+ *val = '\0';
+ grub_env_set (command, val + 1);
+
+ if (grub_strcmp (command, "prefix") == 0)
+ grub_multiboot_change_prefix = 0;
+ }
+ }
+}
+
void
grub_machine_init (void)
{
@@ -214,6 +279,15 @@ grub_machine_init (void)
if (! grub_os_area_addr)
grub_fatal ("no upper memory");
+ if (startup_multiboot_info)
+ {
+ /* Move MBI to a safe place. */
+ grub_memmove (&kern_multiboot_info, startup_multiboot_info,
+ sizeof (struct multiboot_info));
+
+ grub_parse_multiboot_cmdline ();
+ }
+
grub_tsc_init ();
}
=== modified file 'kern/i386/pc/startup.S'
--- kern/i386/pc/startup.S 2010-04-05 13:59:32 +0000
+++ kern/i386/pc/startup.S 2010-06-15 11:02:19 +0000
@@ -142,6 +142,8 @@ multiboot_header:
multiboot_entry:
.code32
+ movl %ebx, EXT_C(startup_multiboot_info)
+
/* obtain the boot device */
movl 12(%ebx), %edx
@@ -161,20 +163,38 @@ multiboot_entry:
jmp *%eax
multiboot_trampoline:
+ /* remember the original boot information */
+ movl EXT_C(grub_install_dos_part), %eax
+ orl %eax, %eax
+ jns 1f
+ movb $0xFF, %al
+1:
+ movl EXT_C(grub_install_bsd_part), %ebx
+ orl %ebx, %ebx
+ jns 2f
+ movb $0xFF, %bl
+2:
+ movb %al, %bh
+
/* fill the boot information */
movl %edx, %eax
shrl $8, %eax
+ cmpw %ax, %bx
+ je 3f
+ /* doesn't match the original */
+ movb $1, EXT_C(grub_multiboot_change_prefix)
+3:
xorl %ebx, %ebx
cmpb $0xFF, %ah
- je 1f
+ je 4f
movb %ah, %bl
movl %ebx, EXT_C(grub_install_dos_part)
-1:
+4:
cmpb $0xFF, %al
- je 2f
+ je 5f
movb %al, %bl
movl %ebx, EXT_C(grub_install_bsd_part)
-2:
+5:
shrl $24, %edx
movb $0xFF, %dh
/* enter the usual booting */
@@ -285,6 +305,8 @@ LOCAL (codestart):
VARIABLE(grub_boot_drive)
.byte 0
+VARIABLE(grub_multiboot_change_prefix)
+ .byte 0
.p2align 2 /* force 4-byte alignment */
=== modified file 'util/i386/pc/grub-setup.c'
--- util/i386/pc/grub-setup.c 2010-06-11 20:31:16 +0000
+++ util/i386/pc/grub-setup.c 2010-06-14 16:29:54 +0000
@@ -99,6 +99,7 @@ setup (const char *dir,
struct grub_boot_blocklist *first_block, *block;
grub_int32_t *install_dos_part, *install_bsd_part;
grub_int32_t dos_part, bsd_part;
+ char *prefix;
char *tmp_img;
int i;
grub_disk_addr_t first_sector;
@@ -230,6 +231,8 @@ setup (const char *dir,
+ GRUB_KERNEL_MACHINE_INSTALL_DOS_PART);
install_bsd_part = (grub_int32_t *) (core_img + GRUB_DISK_SECTOR_SIZE
+ GRUB_KERNEL_MACHINE_INSTALL_BSD_PART);
+ prefix = (char *) (core_img + GRUB_DISK_SECTOR_SIZE +
+ GRUB_KERNEL_MACHINE_PREFIX);
/* Open the root device and the destination device. */
root_dev = grub_device_open (root);
@@ -305,6 +308,18 @@ setup (const char *dir,
dos_part = root_dev->disk->partition->number;
bsd_part = -1;
}
+
+ if (prefix[0] != '(')
+ {
+ char *root_part_name, *new_prefix;
+
+ root_part_name =
+ grub_partition_get_name (root_dev->disk->partition);
+ new_prefix = xasprintf ("(,%s)%s", root_part_name, prefix);
+ strcpy (prefix, new_prefix);
+ free (new_prefix);
+ free (root_part_name);
+ }
}
else
dos_part = bsd_part = -1;
Thanks,
--
Colin Watson [cjwat...@ubuntu.com]
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