From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([65.50.211.133]:43086 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750984AbdBAVmr (ORCPT ); Wed, 1 Feb 2017 16:42:47 -0500 Received: from clnet-p099-196.ikbnet.co.at ([83.175.99.196] helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.87 #1 (Red Hat Linux)) id 1cZ2fu-0003dW-I1 for linux-xfs@vger.kernel.org; Wed, 01 Feb 2017 21:42:47 +0000 From: Christoph Hellwig Subject: [PATCH 1/4] xfs: reject all unaligned direct writes to reflinked files Date: Wed, 1 Feb 2017 22:42:36 +0100 Message-Id: <1485985359-971-2-git-send-email-hch@lst.de> In-Reply-To: <1485985359-971-1-git-send-email-hch@lst.de> References: <1485985359-971-1-git-send-email-hch@lst.de> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: linux-xfs@vger.kernel.org We currently fall back from direct to buffered writes if we detect a remaining shared extent in the iomap_begin callback. But by the time iomap_begin is called for the potentially unaligned end block we might have already written most of the data to disk, which we'd now write again using buffered I/O. To avoid this reject all writes to reflinked files before starting I/O so that we are guaranteed to only write the data once. The alternative would be to unshare the unaligned start and/or end block before doing the I/O. I think that's doable, and will actually be required to support reflinks on DAX file system. But it will take a little more time and I'd rather get rid of the double write ASAP. Signed-off-by: Christoph Hellwig Reviewed-by: Brian Foster --- fs/xfs/xfs_file.c | 7 +++++++ fs/xfs/xfs_iomap.c | 12 +----------- 2 files changed, 8 insertions(+), 11 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index bbb9eb6..06236bf 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -527,6 +527,13 @@ xfs_file_dio_aio_write( if ((iocb->ki_pos & mp->m_blockmask) || ((iocb->ki_pos + count) & mp->m_blockmask)) { unaligned_io = 1; + + /* + * We can't properly handle unaligned direct I/O to reflink + * files yet, as we can't unshare a partial block. + */ + if (xfs_is_reflink_inode(ip)) + return -EREMCHG; iolock = XFS_IOLOCK_EXCL; } else { iolock = XFS_IOLOCK_SHARED; diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index 767208f..d17aa3b 100644 --- a/fs/xfs/xfs_iomap.c +++ b/fs/xfs/xfs_iomap.c @@ -1026,17 +1026,7 @@ xfs_file_iomap_begin( if (error) goto out_unlock; - /* - * We're here because we're trying to do a directio write to a - * region that isn't aligned to a filesystem block. If the - * extent is shared, fall back to buffered mode to handle the - * RMW. - */ - if (!(flags & IOMAP_REPORT) && shared) { - trace_xfs_reflink_bounce_dio_write(ip, &imap); - error = -EREMCHG; - goto out_unlock; - } + ASSERT((flags & IOMAP_REPORT) || !shared); } if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) { -- 2.1.4