Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751833AbbG3Pbm (ORCPT ); Thu, 30 Jul 2015 11:31:42 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:37339 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750819AbbG3Pbk (ORCPT ); Thu, 30 Jul 2015 11:31:40 -0400 Subject: Re: [PATCH v8 4/6] block: loop: prepare for supporing direct IO To: Ming Lei , Jens Axboe , linux-kernel@vger.kernel.org References: <1438256184-23645-1-git-send-email-ming.lei@canonical.com> <1438256184-23645-5-git-send-email-ming.lei@canonical.com> Cc: Zach Brown , Christoph Hellwig , Maxim Patlasov , Andrew Morton , Alexander Viro , Tejun Heo , Dave Chinner , linux-api@vger.kernel.org From: Dave Kleikamp Message-ID: <55BA432F.3050603@oracle.com> Date: Thu, 30 Jul 2015 10:30:55 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <1438256184-23645-5-git-send-email-ming.lei@canonical.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5672 Lines: 179 On 07/30/2015 06:36 AM, Ming Lei wrote: > This patches provides one interface for enabling direct IO > from user space: > > - userspace(such as losetup) can pass 'file' which is > opened/fcntl as O_DIRECT > > Also __loop_update_dio() is introduced to check if direct I/O > can be used on current loop setting. > > The last big change is to introduce LO_FLAGS_DIRECT_IO flag > for userspace to know if direct IO is used to access backing > file. lo->use_dio and LO_FLAGS_DIRECT_IO seem redundant. Wouldn't it be simpler to use one or the other? > > Cc: linux-api@vger.kernel.org > Signed-off-by: Ming Lei > --- > drivers/block/loop.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++- > drivers/block/loop.h | 2 ++ > include/uapi/linux/loop.h | 1 + > 3 files changed, 65 insertions(+), 1 deletion(-) > > diff --git a/drivers/block/loop.c b/drivers/block/loop.c > index 1875aad..799cc23 100644 > --- a/drivers/block/loop.c > +++ b/drivers/block/loop.c > @@ -164,6 +164,47 @@ static loff_t get_loop_size(struct loop_device *lo, struct file *file) > return get_size(lo->lo_offset, lo->lo_sizelimit, file); > } > > +static void __loop_update_dio(struct loop_device *lo, bool dio) > +{ > + struct file *file = lo->lo_backing_file; > + struct inode *inode = file->f_mapping->host; > + bool use_dio; > + unsigned dio_align = inode->i_sb->s_bdev ? > + (bdev_io_min(inode->i_sb->s_bdev) - 1) : 0; > + > + /* > + * We support direct I/O only if lo_offset is aligned > + * with the min I/O size of backing device. > + * > + * Request's offset and size will be checked in I/O path. > + */ > + if (dio) { > + if (!dio_align || (lo->lo_offset & dio_align)) > + use_dio = false; > + else > + use_dio = true; > + } else { > + use_dio = false; > + } > + > + /* flush dirty pages before changing direct IO */ > + vfs_fsync(file, 0); > + > + /* > + * The flag of LO_FLAGS_DIRECT_IO is handled similarly with > + * LO_FLAGS_READ_ONLY, both are set from kernel, and losetup > + * will get updated by ioctl(LOOP_GET_STATUS) > + */ > + blk_mq_freeze_queue(lo->lo_queue); > + lo->use_dio = use_dio; > + lo->dio_align = dio_align; > + if (use_dio) > + lo->lo_flags |= LO_FLAGS_DIRECT_IO; > + else > + lo->lo_flags &= ~LO_FLAGS_DIRECT_IO; > + blk_mq_unfreeze_queue(lo->lo_queue); > +} > + > static int > figure_loop_size(struct loop_device *lo, loff_t offset, loff_t sizelimit) > { > @@ -173,8 +214,12 @@ figure_loop_size(struct loop_device *lo, loff_t offset, loff_t sizelimit) > > if (unlikely((loff_t)x != size)) > return -EFBIG; > - if (lo->lo_offset != offset) > + if (lo->lo_offset != offset) { > lo->lo_offset = offset; > + > + /* update dio if lo_offset is changed*/ > + __loop_update_dio(lo, lo->use_dio); > + } > if (lo->lo_sizelimit != sizelimit) > lo->lo_sizelimit = sizelimit; > set_capacity(lo->lo_disk, x); > @@ -421,6 +466,11 @@ struct switch_request { > struct completion wait; > }; > > +static inline void loop_update_dio(struct loop_device *lo) > +{ > + __loop_update_dio(lo, io_is_direct(lo->lo_backing_file)); > +} > + > /* > * Do the actual switch; called from the BIO completion routine > */ > @@ -441,6 +491,7 @@ static void do_loop_switch(struct loop_device *lo, struct switch_request *p) > mapping->host->i_bdev->bd_block_size : PAGE_SIZE; > lo->old_gfp_mask = mapping_gfp_mask(mapping); > mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS)); > + loop_update_dio(lo); > } > > /* > @@ -627,11 +678,19 @@ static ssize_t loop_attr_partscan_show(struct loop_device *lo, char *buf) > return sprintf(buf, "%s\n", partscan ? "1" : "0"); > } > > +static ssize_t loop_attr_dio_show(struct loop_device *lo, char *buf) > +{ > + int dio = (lo->lo_flags & LO_FLAGS_DIRECT_IO); > + > + return sprintf(buf, "%s\n", dio ? "1" : "0"); > +} > + > LOOP_ATTR_RO(backing_file); > LOOP_ATTR_RO(offset); > LOOP_ATTR_RO(sizelimit); > LOOP_ATTR_RO(autoclear); > LOOP_ATTR_RO(partscan); > +LOOP_ATTR_RO(dio); > > static struct attribute *loop_attrs[] = { > &loop_attr_backing_file.attr, > @@ -639,6 +698,7 @@ static struct attribute *loop_attrs[] = { > &loop_attr_sizelimit.attr, > &loop_attr_autoclear.attr, > &loop_attr_partscan.attr, > + &loop_attr_dio.attr, > NULL, > }; > > @@ -783,6 +843,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode, > if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync) > blk_queue_flush(lo->lo_queue, REQ_FLUSH); > > + loop_update_dio(lo); > set_capacity(lo->lo_disk, size); > bd_set_size(bdev, size << 9); > loop_sysfs_init(lo); > diff --git a/drivers/block/loop.h b/drivers/block/loop.h > index b6c7d21..63f8e14 100644 > --- a/drivers/block/loop.h > +++ b/drivers/block/loop.h > @@ -58,6 +58,8 @@ struct loop_device { > struct mutex lo_ctl_mutex; > struct kthread_worker worker; > struct task_struct *worker_task; > + unsigned dio_align; > + bool use_dio; > > struct request_queue *lo_queue; > struct blk_mq_tag_set tag_set; > diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h > index e0cecd2..949851c 100644 > --- a/include/uapi/linux/loop.h > +++ b/include/uapi/linux/loop.h > @@ -21,6 +21,7 @@ enum { > LO_FLAGS_READ_ONLY = 1, > LO_FLAGS_AUTOCLEAR = 4, > LO_FLAGS_PARTSCAN = 8, > + LO_FLAGS_DIRECT_IO = 16, > }; > > #include /* for __kernel_old_dev_t */ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/