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

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>

diff --git a/docs/grub.texi b/docs/grub.texi
index f8b4b3b21a7fa6e1ac3d55afe0238709d60110b4..f6c7f46b319594649c1a4345af8e2aa38fa230af 100644 (file)
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -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

diff --git a/grub-core/kern/fs.c b/grub-core/kern/fs.c
index c698295bcb410c466ecfd77a68e5b6fd875aca2d..e0d7e16a29405ee29a955a53f0730e4dc424baea 100644 (file)
--- a/grub-core/kern/fs.c
+++ b/grub-core/kern/fs.c
@@ -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)))