commit e012b78cf5bc42f20ef1a1f78383035f2293ceea
author Paolo Bonzini <pbonzini@redhat.com> Wed Dec 17 16:09:59 2014 +0100
committer Stefan Hajnoczi <stefanha@redhat.com> Tue Jan 13 11:47:56 2015 +0000
tree e4f047daaccf6c044eba955e7f68250902f2ff01
parent fcf5def1ab0f94ff120b7141c943b517d2ece83d

block: do not allocate an iovec per read of a growable/zero_after_eof BDS

Most reads do not go past the end of the file, and they can use the
input QEMUIOVector instead of creating one.  This removes the
qemu_iovec_* functions from the profile.

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

block.c

diff --git a/block.c b/block.c
index 4165d42..58f8042 100644
--- a/block.c
+++ b/block.c
@@ -3034,18 +3034,16 @@
 
         max_nb_sectors = ROUND_UP(MAX(0, total_sectors - sector_num),
                                   align >> BDRV_SECTOR_BITS);
-        if (max_nb_sectors > 0) {
+        if (nb_sectors < max_nb_sectors) {
+            ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
+        } else if (max_nb_sectors > 0) {
             QEMUIOVector local_qiov;
-            size_t local_sectors;
-
-            max_nb_sectors = MIN(max_nb_sectors, SIZE_MAX / BDRV_SECTOR_BITS);
-            local_sectors = MIN(max_nb_sectors, nb_sectors);
 
             qemu_iovec_init(&local_qiov, qiov->niov);
             qemu_iovec_concat(&local_qiov, qiov, 0,
-                              local_sectors * BDRV_SECTOR_SIZE);
+                              max_nb_sectors * BDRV_SECTOR_SIZE);
 
-            ret = drv->bdrv_co_readv(bs, sector_num, local_sectors,
+            ret = drv->bdrv_co_readv(bs, sector_num, max_nb_sectors,
                                      &local_qiov);
 
             qemu_iovec_destroy(&local_qiov);