From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752904AbaCaOV6 (ORCPT ); Mon, 31 Mar 2014 10:21:58 -0400 Received: from mail-ie0-f175.google.com ([209.85.223.175]:44821 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbaCaOV5 (ORCPT ); Mon, 31 Mar 2014 10:21:57 -0400 Date: Mon, 31 Mar 2014 10:21:53 -0400 From: Conrad Meyer To: OGAWA Hirofumi Cc: Conrad Meyer , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] fs: FAT: Add support for DOS 1.x formatted volumes Message-ID: <20140331102153.476da7b1@m> In-Reply-To: <87ioqufom3.fsf@devron.myhome.or.jp> References: <1396120235-27844-1-git-send-email-cse.cem@gmail.com> <87ioqufom3.fsf@devron.myhome.or.jp> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 31 Mar 2014 23:07:32 +0900 OGAWA Hirofumi wrote: > Conrad Meyer writes: > > > +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) > > + return; > > Probably, too weak detection to use by default. So, how > about to use mount option to enable this? > > And only if user asked to enable explicitly by mount > option, allow this format. Okay. Do you have a preference for option name? "archaicdos", "dos1x", "guessbpb", other? > > + bd_sects = > > part_nr_sects_read(sb->s_bdev->bd_part); > > + for (di = floppy_defaults; di->nr_sectors; 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); > > + return; > > + } > > + > > + fat_msg(sb, KERN_INFO, > > + "Volume lacks BPB but looks like archaic > > DOS; assuming default BPB values"); + > > + b->sec_per_clus = di->sec_per_clus; > > + put_unaligned_le16(di->dir_entries, > > &b->dir_entries); > > + b->media = di->media; > > + b->fat_length = cpu_to_le16(di->fat_length); > > + put_unaligned_le16(SECTOR_SIZE, &b->sector_size); > > + b->reserved = cpu_to_le16(1); > > + b->fats = 2; > > + put_unaligned_le16(bd_sects, &b->sectors); > > +} > > + > > +/* > > * Read the super block of an MS-DOS FS. > > */ > > int fat_fill_super(struct super_block *sb, void *data, > > int silent, int isvfat, @@ -1297,6 +1387,8 @@ int > > fat_fill_super(struct super_block *sb, void *data, int > > silent, int isvfat, } > > b = (struct fat_boot_sector *) bh->b_data; > > + fat_update_archaic_boot_sector(sb, b); > > This would be better to set sbi->* directly, not via > modified BPB. Hm, I thought so too, but there are lots of sbi-> fields and I didn't want to duplicate any shared filling logic in a different place. But I will make the change... > > > if (!b->reserved) { > > if (!silent) > > fat_msg(sb, KERN_ERR, "bogus > > number of reserved sectors"); @@ -1364,6 +1456,7 @@ int > > fat_fill_super(struct super_block *sb, void *data, int > > silent, int isvfat, goto out_fail; } > > b = (struct fat_boot_sector *) > > bh->b_data; > > + fat_update_archaic_boot_sector(sb, b); > > This doesn't need. If logical_sector_size is 512, this > format doesn't work. Right. Okay, give me some time to revise a v3 patch. Thanks, Conrad