[PATCH] disk: Move hardcoded max disk size literal to a GRUB_DISK_MAX_SECTORS in disk.h

[Glenn Washburn]

There is a hardcoded maximum disk size that can be read or written from,
currently set at 1EiB in grub_disk_adjust_range. Move the literal into a
macro in disk.h, so our assumptions are more visible. This hard coded limit
does not prevent using larger disks, just grub won't read/write past the
limit. The comment accompanying this restriction didn't quite make sense to
me, so its been modified.

Signed-off-by: Glenn Washburn <development@efficientek.com>
---
 grub-core/kern/disk_common.c | 13 +++++++------
 include/grub/disk.h          |  6 ++++++
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/grub-core/kern/disk_common.c b/grub-core/kern/disk_common.c
index 5b92f670b..d20ed20d2 100644
--- a/grub-core/kern/disk_common.c
+++ b/grub-core/kern/disk_common.c
@@ -32,13 +32,14 @@ grub_disk_adjust_range (grub_disk_t disk, grub_disk_addr_t 
*sector,
   /* Transform total_sectors to number of 512B blocks.  */
   total_sectors = grub_disk_from_native_sector (disk, disk->total_sectors);
 
-  /* Some drivers have problems with disks above reasonable.
-     Treat unknown as 1EiB disk. While on it, clamp the size to 1EiB.
-     Just one condition is enough since GRUB_DISK_UNKNOWN_SIZE << ls is always
-     above 9EiB.
+  /*
+     Some drivers have problems with disks above reasonable sizes.
+     Clamp the size to GRUB_DISK_MAX_SECTORS. Just one condition is enough
+     since GRUB_DISK_UNKNOWN_SIZE is always above GRUB_DISK_MAX_SECTORS,
+     assuming a maximum 4KiB sector size.
   */
-  if (total_sectors > (1ULL << 51))
-    total_sectors = (1ULL << 51);
+  if (total_sectors > GRUB_DISK_MAX_SECTORS)
+    total_sectors = GRUB_DISK_MAX_SECTORS;
 
   if ((total_sectors <= *sector
        || ((*offset + size + GRUB_DISK_SECTOR_SIZE - 1)
diff --git a/include/grub/disk.h b/include/grub/disk.h
index 1a9e8fcf4..0bf08091f 100644
--- a/include/grub/disk.h
+++ b/include/grub/disk.h
@@ -157,6 +157,12 @@ struct grub_disk_memberlist
 typedef struct grub_disk_memberlist *grub_disk_memberlist_t;
 #endif
 
+/*
+   Some drivers have problems with disks above reasonable sizes.
+   Set max disk size at 1EiB.
+*/
+#define GRUB_DISK_MAX_SECTORS  (1ULL << (60 - 9))
+
 /* The sector size.  */
 #define GRUB_DISK_SECTOR_SIZE  0x200
 #define GRUB_DISK_SECTOR_BITS  9
-- 
2.27.0