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dataplane: handle misaligned virtio-blk requests

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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 <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2013-01-11 16:41:29 +01:00 committed by Kevin Wolf
parent b5ef1aab94
commit de0161c0d5
1 changed files with 40 additions and 0 deletions
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40
hw/dataplane/virtio-blk.c
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@ -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 */
struct iovec *bounce_iov; /* used if guest buffers are unaligned */
QEMUIOVector *read_qiov; /* for read completion /w bounce buffer */
} VirtIOBlockRequest;
struct VirtIOBlockDataPlane {
@ -89,6 +91,18 @@ 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_iov);
qemu_iovec_from_buf(req->read_qiov, 0, req->bounce_iov->iov_base, len);
qemu_iovec_destroy(req->read_qiov);
g_slice_free(QEMUIOVector, req->read_qiov);
}
if (req->bounce_iov) {
qemu_vfree(req->bounce_iov->iov_base);
g_slice_free(struct iovec, req->bounce_iov);
}
qemu_iovec_from_buf(req->inhdr, 0, &hdr, sizeof(hdr));
qemu_iovec_destroy(req->inhdr);
g_slice_free(QEMUIOVector, req->inhdr);
@ -136,6 +150,30 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
QEMUIOVector *inhdr)
{
struct iocb *iocb;
QEMUIOVector qiov;
struct iovec *bounce_iov = NULL;
QEMUIOVector *read_qiov = NULL;
qemu_iovec_init_external(&qiov, iov, iov_cnt);
if (!bdrv_qiov_is_aligned(s->blk->conf.bs, &qiov)) {
void *bounce_buffer = qemu_blockalign(s->blk->conf.bs, qiov.size);
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);
}
/* Redirect I/O to aligned bounce buffer */
bounce_iov = g_slice_new(struct iovec);
bounce_iov->iov_base = bounce_buffer;
bounce_iov->iov_len = qiov.size;
iov = bounce_iov;
iov_cnt = 1;
}
iocb = ioq_rdwr(&s->ioqueue, read, iov, iov_cnt, offset);
@ -143,6 +181,8 @@ static int do_rdwr_cmd(VirtIOBlockDataPlane *s, bool read,
VirtIOBlockRequest *req = container_of(iocb, VirtIOBlockRequest, iocb);
req->head = head;
req->inhdr = inhdr;
req->bounce_iov = bounce_iov;
req->read_qiov = read_qiov;
return 0;
}