From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:59166) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SmiIf-0004Qc-2F for qemu-devel@nongnu.org; Thu, 05 Jul 2012 05:24:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SmiIZ-0007hD-La for qemu-devel@nongnu.org; Thu, 05 Jul 2012 05:24:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24281) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SmiIZ-0007gx-D0 for qemu-devel@nongnu.org; Thu, 05 Jul 2012 05:24:31 -0400 From: Markus Armbruster References: <1340984094-5451-1-git-send-email-armbru@redhat.com> <1340984094-5451-4-git-send-email-armbru@redhat.com> <4FF45E87.8060100@redhat.com> Date: Thu, 05 Jul 2012 11:23:50 +0200 In-Reply-To: <4FF45E87.8060100@redhat.com> (Kevin Wolf's message of "Wed, 04 Jul 2012 17:17:27 +0200") Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: Re: [Qemu-devel] [PATCH 03/32] vvfat: Fix partition table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Blue Swirl , pbonzini@redhat.com, aliguori@us.ibm.com, qemu-devel@nongnu.org, stefanha@linux.vnet.ibm.com Kevin Wolf writes: > Am 29.06.2012 22:33, schrieb Blue Swirl: >> On Fri, Jun 29, 2012 at 3:34 PM, Markus Armbruster wrote: >>> Unless parameter ":floppy:" is given, vvfat creates a virtual image >>> with DOS MBR defining a single partition which holds the FAT file >>> system. The size of the virtual image depends on the width of the >>> FAT: 32 MiB (CHS 64, 16, 63) for 12 bit FAT, 504 MiB (CHS 1024, 16, >>> 63) for 16 and 32 bit FAT, leaving (64*16-1)*63 = 64449 and >>> (1024*16-1)*64 = 1032129 sectors for the partition. >>> >>> However, it screws up the end of the partition in the MBR: >>> >>> FAT width param. start CHS end CHS start LBA size >>> :32: 0,1,1 1023,14,63 63 1032065 >>> :16: 0,1,1 1023,14,55 63 1032057 >>> :12: 0,1,1 63,14,55 63 64377 >>> >>> The actual FAT file system nevertheless assumes the partition has >>> 1032129 or 64449 sectors. Oops. >>> >>> Signed-off-by: Markus Armbruster >>> --- >>> block/vvfat.c | 7 ++++--- >>> 1 files changed, 4 insertions(+), 3 deletions(-) >>> >>> diff --git a/block/vvfat.c b/block/vvfat.c >>> index 0fd3367..62745b5 100644 >>> --- a/block/vvfat.c >>> +++ b/block/vvfat.c >>> @@ -394,11 +394,12 @@ static void init_mbr(BDRVVVFATState* s) >>> >>> /* LBA is used when partition is outside the CHS geometry */ >>> lba = sector2CHS(s->bs, &partition->start_CHS, s->first_sectors_number-1); >>> - lba|= sector2CHS(s->bs, &partition->end_CHS, s->sector_count); >>> + lba |= sector2CHS(s->bs, &partition->end_CHS, s->bs->total_sectors - 1); >>> >>> /*LBA partitions are identified only by start/length_sector_long not by CHS*/ >>> - partition->start_sector_long =cpu_to_le32(s->first_sectors_number-1); >>> - partition->length_sector_long=cpu_to_le32(s->sector_count - s->first_sectors_number+1); >>> + partition->start_sector_long = cpu_to_le32(s->first_sectors_number-1); >> >> Spaces around '-'. Thanks for fixing the other cases, BTW. > > For compensation there's an extra space before the '='. The original lined up the two '='. I preserved that. Not that I care for it. Want me to drop the extra space? >>> + partition->length_sector_long = cpu_to_le32(s->bs->total_sectors >>> + - s->first_sectors_number + 1); > > Just wondering... This should be the same as s->sector_count, right? Hmm. vvfat_open() assigns: s->sector_count = cyls * heads * secs - (s->first_sectors_number - 1); bs->total_sectors = cyls * heads * secs; But it then changes it minds and does: s->sector_count = s->faked_sectors + s->sectors_per_cluster*s->cluster_count; > This whole geometry calculation code in vvfat is way too convoluted to > understand when you haven't looked at it for some months... Yes, it is. I was briefly tempted to replace it, but then decided to limit my footprint in this buck-crazy block driver to minimal bug fixes.