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SubjectRe: [PATCH v6] fs: FAT: Add support for DOS 1.x formatted volumes
Date
Conrad Meyer <cse.cem@gmail.com> writes:

> 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:
> [1].
>
> Fixes kernel.org bug #42617.
>
> [0]: https://en.wikipedia.org/wiki/File_Allocation_Table#Exceptions
> [1]: http://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html
>
> Signed-off-by: Conrad Meyer <cse.cem@gmail.com>
> ---
> Changes since v5:
> * Leave the bulk of sbi-> filling logic to the aptly named fat_fill_super()
> * Create separate structure for deserialized BPB values
> * fat_read_bpb() deserializes BPB from raw fat_boot_sector and performs
> validations
> * fat_read_static_bpb() validates raw fat_boot_sector as dos1x and fills in
> BPB values from table
>
> Thanks,
> Conrad
> ---
> fs/fat/fat.h | 28 ++++-
> fs/fat/inode.c | 316 +++++++++++++++++++++++++++++++++++++++++++--------------
> 2 files changed, 267 insertions(+), 77 deletions(-)
>
> diff --git a/fs/fat/fat.h b/fs/fat/fat.h
> index 7270bdb..bcb0d67 100644
> --- a/fs/fat/fat.h
> +++ b/fs/fat/fat.h
> @@ -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 */
> };

OK. Looks good basically.

Another one I am also forgetting. Need to update show_options() and
Documents/fs/vfat.txt for new option.

Thanks.
--
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>


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