commit 6f5f060b736cedc2d962114d20805fdd2889513a
author Kevin Wolf <kwolf@redhat.com> Mon Sep 13 18:24:10 2010 +0200
committer Kevin Wolf <kwolf@redhat.com> Tue Sep 21 15:39:43 2010 +0200
tree 8589b132acaa662598a1954c4cc5461ed6b204f2
parent bd28f835652e396841bb73080a07bcc08fe21bf0

qcow2: Avoid bounce buffers for AIO write requests

qcow2 used to use bounce buffers for any AIO requests. This does not only imply
unnecessary copying, but also unbounded allocations which should be avoided.

This patch removes bounce buffers from the normal AIO write path. Encrypted
images continue to use a bounce buffer, however with constant size.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2.c

diff --git a/block/qcow2.c b/block/qcow2.c
index 4a688b4..ee3481b 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -331,15 +331,12 @@
     BlockDriverAIOCB common;
     int64_t sector_num;
     QEMUIOVector *qiov;
-    uint8_t *buf;
-    void *orig_buf;
     int remaining_sectors;
     int cur_nr_sectors;	/* number of sectors in current iteration */
     uint64_t bytes_done;
     uint64_t cluster_offset;
     uint8_t *cluster_data;
     BlockDriverAIOCB *hd_aiocb;
-    struct iovec hd_iov;
     QEMUIOVector hd_qiov;
     QEMUBH *bh;
     QCowL2Meta l2meta;
@@ -530,14 +527,7 @@
     acb->sector_num = sector_num;
     acb->qiov = qiov;
 
-    if (!is_write) {
-        qemu_iovec_init(&acb->hd_qiov, qiov->niov);
-    } else if (qiov->niov == 1) {
-        acb->buf = (uint8_t *)qiov->iov->iov_base;
-    } else {
-        acb->buf = acb->orig_buf = qemu_blockalign(bs, qiov->size);
-        qemu_iovec_to_buffer(qiov, acb->buf);
-    }
+    qemu_iovec_init(&acb->hd_qiov, qiov->niov);
 
     acb->bytes_done = 0;
     acb->remaining_sectors = nb_sectors;
@@ -589,7 +579,6 @@
     BlockDriverState *bs = acb->common.bs;
     BDRVQcowState *s = bs->opaque;
     int index_in_cluster;
-    const uint8_t *src_buf;
     int n_end;
 
     acb->hd_aiocb = NULL;
@@ -605,7 +594,7 @@
 
     acb->remaining_sectors -= acb->cur_nr_sectors;
     acb->sector_num += acb->cur_nr_sectors;
-    acb->buf += acb->cur_nr_sectors * 512;
+    acb->bytes_done += acb->cur_nr_sectors * 512;
 
     if (acb->remaining_sectors == 0) {
         /* request completed */
@@ -636,20 +625,27 @@
 
     assert((acb->cluster_offset & 511) == 0);
 
+    qemu_iovec_reset(&acb->hd_qiov);
+    qemu_iovec_copy(&acb->hd_qiov, acb->qiov, acb->bytes_done,
+        acb->cur_nr_sectors * 512);
+
     if (s->crypt_method) {
         if (!acb->cluster_data) {
             acb->cluster_data = qemu_mallocz(QCOW_MAX_CRYPT_CLUSTERS *
                                              s->cluster_size);
         }
-        qcow2_encrypt_sectors(s, acb->sector_num, acb->cluster_data, acb->buf,
-                        acb->cur_nr_sectors, 1, &s->aes_encrypt_key);
-        src_buf = acb->cluster_data;
-    } else {
-        src_buf = acb->buf;
+
+        assert(acb->hd_qiov.size <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
+        qemu_iovec_to_buffer(&acb->hd_qiov, acb->cluster_data);
+
+        qcow2_encrypt_sectors(s, acb->sector_num, acb->cluster_data,
+            acb->cluster_data, acb->cur_nr_sectors, 1, &s->aes_encrypt_key);
+
+        qemu_iovec_reset(&acb->hd_qiov);
+        qemu_iovec_add(&acb->hd_qiov, acb->cluster_data,
+            acb->cur_nr_sectors * 512);
     }
-    acb->hd_iov.iov_base = (void *)src_buf;
-    acb->hd_iov.iov_len = acb->cur_nr_sectors * 512;
-    qemu_iovec_init_external(&acb->hd_qiov, &acb->hd_iov, 1);
+
     BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
     acb->hd_aiocb = bdrv_aio_writev(bs->file,
                                     (acb->cluster_offset >> 9) + index_in_cluster,
@@ -667,9 +663,8 @@
         QLIST_REMOVE(&acb->l2meta, next_in_flight);
     }
 done:
-    if (acb->qiov->niov > 1)
-        qemu_vfree(acb->orig_buf);
     acb->common.cb(acb->common.opaque, ret);
+    qemu_iovec_destroy(&acb->hd_qiov);
     qemu_aio_release(acb);
 }