On Sat, 29 Mar 2014 12:10:35 -0700 Conrad Meyer <ceme...@uw.edu> wrote:
> When possible, infer DOS 2.x BIOS Parameter Block from block device > geometry (for floppies and floppy images). Update in-memory only. We > only perform this update when the entire BPB region is zeroed, like > produced by DOS 1.x-era FORMAT (and other OEM variations on DOS). > > Fixes kernel.org bug #42617. > > BPB default values are inferred from media size and a table.[0] Media > size is assumed to be static for archaic FAT volumes. See also [1]. > > [0]: https://en.wikipedia.org/wiki/File_Allocation_Table#Exceptions > [1]: http://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html > > ... > > --- a/fs/fat/inode.c > +++ b/fs/fat/inode.c > @@ -35,9 +35,47 @@ > #define CONFIG_FAT_DEFAULT_IOCHARSET "" > #endif > > +#define KB_IN_SECTORS 2 > + > static int fat_default_codepage = CONFIG_FAT_DEFAULT_CODEPAGE; > static char fat_default_iocharset[] = CONFIG_FAT_DEFAULT_IOCHARSET; > > +static struct fat_floppy_defaults { > + unsigned nr_sectors; > + unsigned sec_per_clus; > + unsigned dir_entries; > + unsigned media; > + unsigned fat_length; > +} floppy_defaults[] = { > +{ > + .nr_sectors = 160 * KB_IN_SECTORS, > + .sec_per_clus = 1, > + .dir_entries = 64, > + .media = 0xFE, > + .fat_length = 1, > +}, > +{ > + .nr_sectors = 180 * KB_IN_SECTORS, > + .sec_per_clus = 1, > + .dir_entries = 64, > + .media = 0xFC, > + .fat_length = 2, > +}, > +{ > + .nr_sectors = 320 * KB_IN_SECTORS, > + .sec_per_clus = 2, > + .dir_entries = 112, > + .media = 0xFF, > + .fat_length = 1, > +}, > +{ > + .nr_sectors = 360 * KB_IN_SECTORS, > + .sec_per_clus = 2, > + .dir_entries = 112, > + .media = 0xFD, > + .fat_length = 2, > +}, > +{ 0 } }; We don't really need this EOF element. > static int fat_add_cluster(struct inode *inode) > { > @@ -1246,6 +1284,58 @@ static unsigned long calc_fat_clusters(struct > super_block *sb) > } > > /* > + * If this FAT filesystem is archaic (lacking a BIOS Parameter Block, ca. DOS > + * 1.x), fix it up in-place by creating a DOS 2.x BIOS Parameter Block from > + * defaults for the media size. > + */ > +static void fat_update_archaic_boot_sector(struct super_block *sb, > + struct fat_boot_sector *b) > +{ > + struct fat_floppy_defaults *di; > + sector_t bd_sects; > + > + /* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */ > + if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) > + return; > + > + /* > + * If any value in this region is non-zero, don't assume it is archaic > + * DOS. > + */ > + if (get_unaligned_le16(&b->sector_size) != 0 || b->sec_per_clus != 0 || > + b->reserved != 0 || b->fats != 0 || > + get_unaligned_le16(&b->dir_entries) != 0 || > + get_unaligned_le16(&b->sectors) != 0 || b->media != 0 || > + b->fat_length != 0 || b->secs_track != 0 || b->heads != 0 || > + b->secs_track != 0 || b->heads != 0) Impressive! > + return; > + > + bd_sects = part_nr_sects_read(sb->s_bdev->bd_part); > + for (di = floppy_defaults; di->nr_sectors; di++) { Can do something like for (di = floppy_defaults; di < floppy_defaults + ARRAY_SIZE(floppy_defaults); di++) { > + if (di->nr_sectors == bd_sects) > + break; > + } > + if (di->nr_sectors == 0) { > + fat_msg(sb, KERN_WARNING, > + "DOS volume lacks BPB and isn't a recognized floppy > size (%ld sectors)", > + (long)bd_sects); sector_t can be u64 on 32-bit so one should really use %Lu and cast to u64. > > ... > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
