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SubjectRe: [PATCH 3/5] lguest: replace VIRTIO_F_BARRIER support with VIRTIO_F_FLUSH support
VIRTIO_F_BARRIER is deprecated.  Replace it with VIRTIO_F_FLUSH
support.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Christoph Hellwig <hch@lst.de>
---
FUA support dropped as suggested by Christoph. Rusty, can you please
ack this version too? I tested it with the updated virtio_blk and it
works fine.
Thanks.

Documentation/lguest/lguest.c | 29 +++++++++--------------------
1 file changed, 9 insertions(+), 20 deletions(-)
Index: block/Documentation/lguest/lguest.c
===================================================================
--- block.orig/Documentation/lguest/lguest.c
+++ block/Documentation/lguest/lguest.c
@@ -1639,15 +1639,6 @@ static void blk_request(struct virtqueue
off = out->sector * 512;

/*
- * The block device implements "barriers", where the Guest indicates
- * that it wants all previous writes to occur before this write. We
- * don't have a way of asking our kernel to do a barrier, so we just
- * synchronize all the data in the file. Pretty poor, no?
- */
- if (out->type & VIRTIO_BLK_T_BARRIER)
- fdatasync(vblk->fd);
-
- /*
* In general the virtio block driver is allowed to try SCSI commands.
* It'd be nice if we supported eject, for example, but we don't.
*/
@@ -1679,6 +1670,13 @@ static void blk_request(struct virtqueue
/* Die, bad Guest, die. */
errx(1, "Write past end %llu+%u", off, ret);
}
+
+ wlen = sizeof(*in);
+ *in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
+ } else if (out->type & VIRTIO_BLK_T_FLUSH) {
+ /* Flush */
+ ret = fdatasync(vblk->fd);
+ verbose("FLUSH fdatasync: %i\n", ret);
wlen = sizeof(*in);
*in = (ret >= 0 ? VIRTIO_BLK_S_OK : VIRTIO_BLK_S_IOERR);
} else {
@@ -1702,15 +1700,6 @@ static void blk_request(struct virtqueue
}
}

- /*
- * OK, so we noted that it was pretty poor to use an fdatasync as a
- * barrier. But Christoph Hellwig points out that we need a sync
- * *afterwards* as well: "Barriers specify no reordering to the front
- * or the back." And Jens Axboe confirmed it, so here we are:
- */
- if (out->type & VIRTIO_BLK_T_BARRIER)
- fdatasync(vblk->fd);
-
/* Finished that request. */
add_used(vq, head, wlen);
}
@@ -1735,8 +1724,8 @@ static void setup_block_file(const char
vblk->fd = open_or_die(filename, O_RDWR|O_LARGEFILE);
vblk->len = lseek64(vblk->fd, 0, SEEK_END);

- /* We support barriers. */
- add_feature(dev, VIRTIO_BLK_F_BARRIER);
+ /* We support FLUSH. */
+ add_feature(dev, VIRTIO_BLK_F_FLUSH);

/* Tell Guest how many sectors this device has. */
conf.capacity = cpu_to_le64(vblk->len / 512);

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