[PATCH v9 5/6] block: loop: introduce ioctl command of LOOP_SET_DIRECT_IO

Ming Lei
2015-08-06T08:44:10Z

If loop block is mounted via 'mount -o loop', it isn't easy
to pass file descriptor opened as O_DIRECT, so this patch
introduces a new command to support direct IO for this case.

Cc: linux-api@vger.kernel.org
Signed-off-by: Ming Lei <ming.lei@canonical.com>
---
drivers/block/loop.c | 19 +++++++++++++++++++
include/uapi/linux/loop.h | 1 +
2 files changed, 20 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a56f973..06a737b 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1214,6 +1214,20 @@ static int loop_set_capacity(struct loop_device *lo, struct block_device *bdev)
return figure_loop_size(lo, lo->lo_offset, lo->lo_sizelimit);
}

+static int loop_set_dio(struct loop_device *lo, unsigned long arg)
+{
+ int error = -ENXIO;
+ if (lo->lo_state != Lo_bound)
+ goto out;
+
+ __loop_update_dio(lo, !!arg);
+ if (lo->use_dio == !!arg)
+ return 0;
+ error = -EINVAL;
+ out:
+ return error;
+}
+
static int lo_ioctl(struct block_device *bdev, fmode_t mode,
unsigned int cmd, unsigned long arg)
{
@@ -1257,6 +1271,11 @@ static int lo_ioctl(struct block_device *bdev, fmode_t mode,
if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
err = loop_set_capacity(lo, bdev);
break;
+ case LOOP_SET_DIRECT_IO:
+ err = -EPERM;
+ if ((mode & FMODE_WRITE) || capable(CAP_SYS_ADMIN))
+ err = loop_set_dio(lo, arg);
+ break;
default:
err = lo->ioctl ? lo->ioctl(lo, cmd, arg) : -EINVAL;
}
diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h
index 949851c..c8125ec 100644
--- a/include/uapi/linux/loop.h
+++ b/include/uapi/linux/loop.h
@@ -87,6 +87,7 @@ struct loop_info64 {
#define LOOP_GET_STATUS64 0x4C05
#define LOOP_CHANGE_FD 0x4C06
#define LOOP_SET_CAPACITY 0x4C07
+#define LOOP_SET_DIRECT_IO 0x4C08

/* /dev/loop-control interface */
#define LOOP_CTL_ADD 0x4C80
--
1.9.1