[PATCH 10/7] [BLOCK] Add BLKDISCARD ioctl to allow userspace to discard sectors

[David Woodhouse <dwmw2@infradead.org>]

We may well want mkfs tools to use this to mark the whole device as
unwanted before they format it, for example.

The ioctl takes a pair of uint64_ts, which are start offset and length
in _bytes_. Although at the moment it might make sense for them both to
be in 512-byte sectors, I don't want to limit the ABI to that.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
---
 block/compat_ioctl.c |    1 +
 block/ioctl.c        |   74 ++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h   |    1 +
 3 files changed, 76 insertions(+), 0 deletions(-)

diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index c23177e..1e559fb 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -788,6 +788,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 		return compat_hdio_getgeo(disk, bdev, compat_ptr(arg));
 	case BLKFLSBUF:
 	case BLKROSET:
+	case BLKDISCARD:
 	/*
 	 * the ones below are implemented in blkdev_locked_ioctl,
 	 * but we call blkdev_ioctl, which gets the lock for us
diff --git a/block/ioctl.c b/block/ioctl.c
index 77185e5..8193fbb 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -111,6 +111,69 @@ static int blkdev_reread_part(struct block_device *bdev)
 	return res;
 }
 
+static void blk_ioc_discard_endio(struct bio *bio, int err)
+{
+	if (err) {
+		if (err == -EOPNOTSUPP)
+			set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
+		clear_bit(BIO_UPTODATE, &bio->bi_flags);
+	}
+	complete(bio->bi_private);
+}
+
+static int blk_ioctl_discard(struct block_device *bdev, uint64_t start,
+			     uint64_t len)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+	int ret = 0;
+
+	if (start & 511)
+		return -EINVAL;
+	if (len & 511)
+		return -EINVAL;
+	start >>= 9;
+	len >>= 9;
+
+	if (start + len > (bdev->bd_inode->i_size >> 9))
+		return -EINVAL;
+
+	if (!q->prepare_discard_fn)
+		return -EOPNOTSUPP;
+
+	while (len && !ret) {
+		DECLARE_COMPLETION_ONSTACK(wait);
+		struct bio *bio;
+
+		bio = bio_alloc(GFP_KERNEL, 0);
+		if (!bio)
+			return -ENOMEM;
+
+		bio->bi_end_io = blk_ioc_discard_endio;
+		bio->bi_bdev = bdev;
+		bio->bi_private = &wait;
+		bio->bi_sector = start;
+
+		if (len > q->max_hw_sectors) {
+			bio->bi_size = q->max_hw_sectors << 9;
+			len -= q->max_hw_sectors;
+			start += q->max_hw_sectors;
+		} else {
+			bio->bi_size = len << 9;
+			len = 0;
+		}
+		submit_bio(WRITE_DISCARD, bio);
+
+		wait_for_completion(&wait);
+
+		if (bio_flagged(bio, BIO_EOPNOTSUPP))
+			ret = -EOPNOTSUPP;
+		else if (!bio_flagged(bio, BIO_UPTODATE))
+			ret = -EIO;
+		bio_put(bio);
+	}
+	return ret;
+}
+
 static int put_ushort(unsigned long arg, unsigned short val)
 {
 	return put_user(val, (unsigned short __user *)arg);
@@ -258,6 +321,17 @@ int blkdev_ioctl(struct inode *inode, struct file *file, unsigned cmd,
 		set_device_ro(bdev, n);
 		unlock_kernel();
 		return 0;
+
+	case BLKDISCARD: {
+		uint64_t start, len;
+
+		if (get_user(start, (uint64_t __user *)(arg)) ||
+		    get_user(len, (uint64_t __user *)(arg+8)))
+			return -EFAULT;
+
+		return blk_ioctl_discard(bdev, start, len);
+	}
+
 	case HDIO_GETGEO: {
 		struct hd_geometry geo;
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index eb01313..88358ca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -223,6 +223,7 @@ extern int dir_notify_enable;
 #define BLKTRACESTART _IO(0x12,116)
 #define BLKTRACESTOP _IO(0x12,117)
 #define BLKTRACETEARDOWN _IO(0x12,118)
+#define BLKDISCARD _IO(0x12,119)
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */
-- 
1.5.5.1


-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation