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Date: Thu, 30 Jul 2015 10:30:55 -0500
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Ming Lei <ming.lei@...onical.com>, Jens Axboe <axboe@...nel.dk>,
linux-kernel@...r.kernel.org
Cc: Zach Brown <zab@...bo.net>, Christoph Hellwig <hch@...radead.org>,
Maxim Patlasov <mpatlasov@...allels.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Alexander Viro <viro@...iv.linux.org.uk>,
Tejun Heo <tj@...nel.org>, Dave Chinner <david@...morbit.com>,
linux-api@...r.kernel.org
Subject: Re: [PATCH v8 4/6] block: loop: prepare for supporing direct IO
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@...r.kernel.org
> Signed-off-by: Ming Lei <ming.lei@...onical.com>
> ---
> 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 <asm/posix_types.h> /* for __kernel_old_dev_t */
>
--
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