Commit 190a8843 authored by Conrad Meyer's avatar Conrad Meyer Committed by Linus Torvalds

fs/fat/: add support for DOS 1.x formatted volumes

Add structure for parsed BPB information, struct fat_bios_param_block,
and move all of the deserialization and validation logic from
fat_fill_super() into fat_read_bpb().

Add a 'dos1xfloppy' mount option to infer DOS 2.x BIOS Parameter Block
defaults from block device geometry for ancient floppies and floppy
images, as a fall-back from the default BPB parsing logic.

When fat_read_bpb() finds an invalid FAT filesystem and dos1xfloppy is
set, fall back to fat_read_static_bpb().  fat_read_static_bpb()
validates that the entire BPB is zero, and that the floppy has a
DOS-style 8086 code bootstrapping header.  Then it fills in default BPB
values from media size and a table.[0]

Media size is assumed to be static for archaic FAT volumes.  See also:

Fixes bug #42617.


[ fix missed error code]
Signed-off-by: default avatarConrad Meyer <>
Acked-by: default avatarOGAWA Hirofumi <>
Signed-off-by: default avatarOGAWA Hirofumi <>
Tested-by: default avatarAlan Cox <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent a19189e5
......@@ -172,6 +172,11 @@ nfs=stale_rw|nostale_ro
To maintain backward compatibility, '-o nfs' is also accepted,
defaulting to stale_rw
dos1xfloppy -- If set, use a fallback default BIOS Parameter Block
configuration, determined by backing device size. These static
parameters match defaults assumed by DOS 1.x for 160 kiB,
180 kiB, 320 kiB, and 360 kiB floppies and floppy images.
<bool>: 0,1,yes,no,true,false
......@@ -52,7 +52,8 @@ struct fat_mount_options {
usefree:1, /* Use free_clusters for FAT32 */
tz_set:1, /* Filesystem timestamps' offset set */
rodir:1, /* allow ATTR_RO for directory */
discard:1; /* Issue discard requests on deletions */
discard:1, /* Issue discard requests on deletions */
dos1xfloppy:1; /* Assume default BPB for DOS 1.x floppies */
#define FAT_HASH_BITS 8
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