Re: [PATCH] pygrub: look in every partition for something to boot

[David Markey <admin@dmarkey.com>]

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Good job. I've come across this problem before.

On 6 July 2010 11:45, Tim Deegan <Tim.Deegan@citrix.com> wrote:

> pygrub: look in every partition for something to boot, in case
> the OS installer (SLES 10 sp1 in particular) forgets to mark the
> boot partition as active.
>
> Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
>
> diff -r 78b2f1e04c73 tools/pygrub/src/pygrub
> --- a/tools/pygrub/src/pygrub   Tue Jul 06 11:09:36 2010 +0100
> +++ b/tools/pygrub/src/pygrub   Tue Jul 06 11:38:42 2010 +0100
> @@ -50,21 +50,6 @@
>         return True
>     return False
>
> -def get_active_partition(file):
> -    """Find the offset for the start of the first active partition "
> -    "in the disk image file."""
> -
> -    fd = os.open(file, os.O_RDONLY)
> -    buf = os.read(fd, 512)
> -    for poff in (446, 462, 478, 494): # partition offsets
> -        # active partition has 0x80 as the first byte
> -        if struct.unpack("<c", buf[poff:poff+1]) == ('\x80',):
> -            return buf[poff:poff+16]
> -
> -    # if there's not a partition marked as active, fall back to
> -    # the first partition
> -    return buf[446:446+16]
> -
>  SECTOR_SIZE=512
>  DK_LABEL_LOC=1
>  DKL_MAGIC=0xdabe
> @@ -101,25 +86,44 @@
>  FDISK_PART_SOLARIS_OLD=0x82
>  FDISK_PART_GPT=0xee
>
> -def get_fs_offset(file):
> +def get_partition_offsets(file):
>     if not is_disk_image(file):
> -        return 0
> +        # No MBR: assume whole disk filesystem, which is like a
> +        # single partition starting at 0
> +        return [0]
>
> -    partbuf = get_active_partition(file)
> -    if len(partbuf) == 0:
> -        raise RuntimeError, "Unable to find active partition on disk"
> +    part_offs = []
>
> -    offset = struct.unpack("<L", partbuf[8:12])[0] * SECTOR_SIZE
> +    fd = os.open(file, os.O_RDONLY)
> +    buf = os.read(fd, 512)
> +    for poff in (446, 462, 478, 494): # partition offsets
>
> -    type = struct.unpack("<B", partbuf[4:5])[0]
> +        # MBR contains a 16 byte descriptor per partition
> +        partbuf = buf[poff:poff+16]
> +        offset  = struct.unpack("<L", partbuf[8:12])[0] * SECTOR_SIZE
> +        type    = struct.unpack("<B", partbuf[4:5])[0]
> +
> +        # offset == 0 implies this partition is not enabled
> +        if offset == 0:
> +            continue
>
> -    if type == FDISK_PART_SOLARIS or type == FDISK_PART_SOLARIS_OLD:
> -        offset += get_solaris_slice(file, offset)
> +        if type == FDISK_PART_SOLARIS or type == FDISK_PART_SOLARIS_OLD:
> +            try:
> +                offset += get_solaris_slice(file, offset)
> +            except RuntimeError:
> +                continue # no solaris magic at that offset, ignore
> partition
>
> -    if type == FDISK_PART_GPT:
> -        offset = get_fs_offset_gpt(file)
> -
> -    return offset
> +        if type == FDISK_PART_GPT:
> +            offset = get_fs_offset_gpt(file)
> +
> +        # Active partition has 0x80 as the first byte.
> +        # If active, prepend to front of list, otherwise append to back.
> +        if struct.unpack("<c", buf[poff:poff+1]) == ('\x80',):
> +            part_offs.insert(0, offset)
> +        else:
> +            part_offs.append(offset)
> +
> +    return part_offs
>
>  class GrubLineEditor(curses.textpad.Textbox):
>     def __init__(self, screen, startx, starty, line = ""):
> @@ -703,17 +711,40 @@
>     bootfsargs = '"%s"' % incfg["args"]
>     bootfsgroup = re.findall('zfs-bootfs=(.*?)[\s\,\"]', bootfsargs)
>     if bootfsgroup:
> -        fs = fsimage.open(file, get_fs_offset(file), bootfsgroup[0])
> +        bootfsoptions = bootfsgroup[0]
>     else:
> -        fs = fsimage.open(file, get_fs_offset(file))
> +        bootfsoptions = ""
>
> -    chosencfg = sniff_solaris(fs, incfg)
> +    # get list of offsets into file which start partitions
> +    part_offs = get_partition_offsets(file)
>
> -    if not chosencfg["kernel"]:
> -        chosencfg = sniff_netware(fs, incfg)
> +    for offset in part_offs:
> +        try:
> +            fs = fsimage.open(file, offset, bootfsoptions)
>
> -    if not chosencfg["kernel"]:
> -        chosencfg = run_grub(file, entry, fs, incfg["args"])
> +            chosencfg = sniff_solaris(fs, incfg)
> +
> +            if not chosencfg["kernel"]:
> +                chosencfg = sniff_netware(fs, incfg)
> +
> +            if not chosencfg["kernel"]:
> +                chosencfg = run_grub(file, entry, fs, incfg["args"])
> +
> +            # Break as soon as we've found the kernel so that we continue
> +            # to use this fsimage object
> +            if chosencfg["kernel"]:
> +                break
> +            fs = None
> +
> +        except:
> +            # IOErrors raised by fsimage.open
> +            # RuntimeErrors raised by run_grub if no menu.lst present
> +            fs = None
> +            continue
> +
> +    # Did looping through partitions find us a kernel?
> +    if not fs:
> +        raise RuntimeError, "Unable to find partition containing kernel"
>
>     if not_really:
>         bootcfg["kernel"] = "<kernel:%s>" % chosencfg["kernel"]
>
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>

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