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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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