From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45721) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fNg9w-00020q-7f for qemu-devel@nongnu.org; Tue, 29 May 2018 11:03:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fNg9q-0006sS-GH for qemu-devel@nongnu.org; Tue, 29 May 2018 11:03:36 -0400 References: <20180425183223.580566-1-eblake@redhat.com> <20180425183223.580566-3-eblake@redhat.com> <20180528105232.GD4580@localhost.localdomain> From: Eric Blake Message-ID: Date: Tue, 29 May 2018 10:03:18 -0500 MIME-Version: 1.0 In-Reply-To: <20180528105232.GD4580@localhost.localdomain> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 2/8] qcow: Switch get_cluster_offset to be byte-based List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org, "open list:qcow" , Max Reitz On 05/28/2018 05:52 AM, Kevin Wolf wrote: > Am 25.04.2018 um 20:32 hat Eric Blake geschrieben: >> We are gradually moving away from sector-based interfaces, towards >> byte-based. Make the change for the internal helper function >> get_cluster_offset(), by changing n_start and n_end to by byte >> offsets rather than sector indices within the cluster being >> allocated. >> >> A later patch will then switch the qcow driver as a whole over >> to byte-based operation. >> >> Signed-off-by: Eric Blake >> --- >> block/qcow.c | 28 ++++++++++++++-------------- >> 1 file changed, 14 insertions(+), 14 deletions(-) >> >> + for (i = 0; i < s->cluster_size; i += BDRV_SECTOR_SIZE) { >> if (i < n_start || i >= n_end) { >> - memset(s->cluster_data, 0x00, 512); >> + memset(s->cluster_data, 0x00, BDRV_SECTOR_SIZE); >> if (qcrypto_block_encrypt(s->crypto, >> - (start_sect + i) * >> - BDRV_SECTOR_SIZE, >> + start_offset + i, >> s->cluster_data, >> BDRV_SECTOR_SIZE, >> NULL) < 0) { > > This code is still working in blocks of BDRV_SECTOR_SIZE here - which > you do need to keep at least partially because that's the block size > that qcrypto_block_encrypt() works with. qcrypto_block_qcow_encrypt() > even asserts it. > > However, this means that even though n_start and n_end are byte-based > now, the code only works correctly with encrypted images if they are > multiples of BDRV_SECTOR_SIZE. This is currently true and we could > assert it, but it would kind of defeat the purpose of the patch. But in patch 5, I intentionally kept bs->bl.request_alignment at 512, so I'd rather just assert that n_start and n_end are properly aligned than to worry about rounding issues. > > I suppose you could make unaligned n_start/n_end work if you round down > n_start and round up n_end to the next sector boundary for the > comparison with i. For unaligned requests, we would then write a bit > more than is actually necessary, but I think that's okay because we're > initialising a previously unallocated cluster, so we don't overwrite > valid data. The point is that we never have unaligned requests to qcow1. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org