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kern/fs: Allow number of blocks in block list to be optional, defaulting length to device length

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This is primarily useful to do something like "loopback newdev (dev)8+" to
create a device that skips the first 4 KiB, which may contain a container
header, e.g. a non-standard RAID1 header, that GRUB does not recognize. This
would allow that container data to be potentially accessed up to the end of
container, which may be necessary for some layouts that store data at the
end. There is currently not a good way to programmatically get the number
of sectors on a disk to set the appropriate length of the blocklist.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Glenn Washburn 2021-03-21 13:09:10 -05:00 committed by Daniel Kiper
parent 8f35208db4
commit 0c2aaec01d
2 changed files with 11 additions and 5 deletions
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10
docs/grub.texi
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@ -3036,16 +3036,18 @@ snapshot name is omitted.
A block list is used for specifying a file that doesn't appear in the
filesystem, like a chainloader. The syntax is
@code{[@var{offset}]+@var{length}[,[@var{offset}]+@var{length}]@dots{}}.
@code{[@var{offset}]+[@var{length}][,[@var{offset}]+[@var{length}]]@dots{}}.
Here is an example:
@example
@code{0+100,200+1,300+300}
@code{0+100,200+1,300+300,800+}
@end example
This represents that GRUB should read blocks 0 through 99, block 200,
and blocks 300 through 599. If you omit an offset, then GRUB assumes
the offset is zero.
blocks 300 through 599, and blocks 800 until the end of the device.
If you omit an offset, then GRUB assumes the offset is zero. If the
length is omitted, then GRUB assumes the block list extends until the
end of the device.
Like the file name syntax (@pxref{File name syntax}), if a blocklist
does not contain a device name, then GRUB uses GRUB's @dfn{root

6
grub-core/kern/fs.c
View File

@ -173,7 +173,11 @@ grub_fs_blocklist_open (grub_file_t file, const char *name)
}
p++;
blocks[i].length = grub_strtoul (p, &p, 0);
if (*p == '\0' || *p == ',')
blocks[i].length = max_sectors - blocks[i].offset;
else
blocks[i].length = grub_strtoul (p, &p, 0);
if (grub_errno != GRUB_ERR_NONE
|| blocks[i].length == 0
|| (*p && *p != ',' && ! grub_isspace (*p)))