FAT: deal with non-mirrored FATs for FAT32

FAT32 has the option of non-mirrored FATs, used to improve atomicity
of some operations.  If we have non-mirrored FATs, we need to make
sure to read the one FAT which is currently marked active.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/core/fs/fat/fat.c b/core/fs/fat/fat.c
index c89ed78..b036ead 100644 (file)
--- a/core/fs/fat/fat.c
+++ b/core/fs/fat/fat.c
@@ -743,8 +743,14 @@ static int vfat_fs_init(struct fs_info *fs)
        sbi->fat_type = FAT16;
     } else {
        sbi->fat_type = FAT32;
+
        if (clusters > 0x0ffffff4)
            clusters = 0x0ffffff4; /* Maximum possible */
+
+       if (fat.fat32.extended_flags & 0x80) {
+           /* Non-mirrored FATs, we need to read the active one */
+           sbi->fat += (fat.fat32.extended_flags & 0x0f) * sectors_per_fat;
+       }
     }
     sbi->clusters = clusters;