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[Qemu-devel] [PATCH v2 3/3] dataplane: handle misaligned virtio-blk requ
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH v2 3/3] dataplane: handle misaligned virtio-blk requests |
Date: |
Fri, 11 Jan 2013 13:34:57 +0100 |
O_DIRECT on Linux has alignment requirements on I/O buffers and
misaligned requests result in -EINVAL. The Linux virtio_blk guest
driver usually submits aligned requests so I forgot to handle misaligned
requests.
It turns out that virtio-win guest drivers submit misaligned requests.
Handle them using a bounce buffer that meets alignment requirements.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
hw/dataplane/virtio-blk.c | 36 ++++++++++++++++++++++++++++++++++++
1 file changed, 36 insertions(+)
diff --git a/hw/dataplane/virtio-blk.c b/hw/dataplane/virtio-blk.c
index a6696b8..88300a6 100644
--- a/hw/dataplane/virtio-blk.c
+++ b/hw/dataplane/virtio-blk.c
@@ -34,6 +34,8 @@ typedef struct {
struct iocb iocb; /* Linux AIO control block */
QEMUIOVector *inhdr; /* iovecs for virtio_blk_inhdr */
unsigned int head; /* vring descriptor index */
+ void *bounce_buffer; /* used if guest buffers are unaligned */
+ QEMUIOVector *read_qiov; /* for read completion /w bounce buffer */
} VirtIOBlockRequest;
struct VirtIOBlockDataPlane {
@@ -89,6 +91,15 @@ static void complete_request(struct iocb *iocb, ssize_t ret,
void *opaque)
trace_virtio_blk_data_plane_complete_request(s, req->head, ret);
+ if (req->read_qiov) {
+ assert(req->bounce_buffer);
+ qemu_iovec_from_buf(req->read_qiov, 0, req->bounce_buffer, len);
+ qemu_iovec_destroy(req->read_qiov);
+ g_slice_free(QEMUIOVector, req->read_qiov);
+ }
+
+ qemu_vfree(req->bounce_buffer);
+
qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
qemu_iovec_destroy(req->inhdr);
g_slice_free(QEMUIOVector, req->inhdr);
@@ -136,6 +147,29 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
QEMUIOVector *inhdr)
{
struct iocb *iocb;
+ QEMUIOVector qiov;
+ struct iovec bounce_iov;
+ void *bounce_buffer = NULL;
+ QEMUIOVector *read_qiov = NULL;
+
+ qemu_iovec_init_external(&qiov, iov, iov_cnt);
+ if (!bdrv_qiov_is_aligned(s->blk->conf.bs, &qiov)) {
+ /* Redirect I/O to aligned bounce buffer */
+ bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov.size);
+ bounce_iov.iov_base = bounce_buffer;
+ bounce_iov.iov_len = qiov.size;
+ iov = &bounce_iov;
+ iov_cnt = 1;
+
+ if (read) {
+ /* Need to copy back from bounce buffer on completion */
+ read_qiov = g_slice_new(QEMUIOVector);
+ qemu_iovec_init(read_qiov, iov_cnt);
+ qemu_iovec_concat_iov(read_qiov, iov, iov_cnt, 0, qiov.size);
+ } else {
+ qemu_iovec_to_buf(&qiov, 0, bounce_buffer, qiov.size);
+ }
+ }
iocb = ioq_rdwr(&s->ioqueue, read, iov, iov_cnt, offset);
@@ -143,6 +177,8 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
VirtIOBlockRequest *req = container_of(iocb, VirtIOBlockRequest, iocb);
req->head = head;
req->inhdr = inhdr;
+ req->bounce_buffer = bounce_buffer;
+ req->read_qiov = read_qiov;
return 0;
}
--
1.8.0.2