This is the simple approach to making sure that disk writes actually
hit disk before we tell the guest OS that IO has completed. Thanks
to DMA_MULTI_THREAD the performance still seems to be adequate.
A fancier solution would be to make the sync/non-sync behaviour of
the qemu disk backing store tunable from the guest OS, by tuning
the IDE disk write cache on/off with hdparm, and having hw/ide.c
call ->fsync functions in the block backends.
I'm willing to code up the fancy solution if people prefer that.
------------------------------------------------------------------------
Make sure disk writes really made it to disk before we report I/O
completion to the guest domain. The DMA_MULTI_THREAD functionality
from the qemu-dm IDE emulation should make the performance overhead
of synchronous writes bearable, or at least comparable to native
hardware.
Signed-off-by: Rik van Riel <address@hidden>
--- xen-unstable-10712/tools/ioemu/block-bochs.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block-bochs.c 2006-07-28
02:21:08.000000000 -0400
@@ -91,7 +91,7 @@
int fd, i;
struct bochs_header bochs;
- fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+ fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE | O_SYNC);
if (fd < 0) {
fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
if (fd < 0)
--- xen-unstable-10712/tools/ioemu/block.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block.c 2006-07-28 02:19:27.000000000
-0400
@@ -677,7 +677,7 @@
int rv;
#endif
- fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+ fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE | O_SYNC);
if (fd < 0) {
fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
if (fd < 0)
--- xen-unstable-10712/tools/ioemu/block-cloop.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block-cloop.c 2006-07-28
02:17:13.000000000 -0400
@@ -55,7 +55,7 @@
BDRVCloopState *s = bs->opaque;
uint32_t offsets_size,max_compressed_block_size=1,i;
- s->fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
+ s->fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE | O_SYNC);
if (s->fd < 0)
return -1;
bs->read_only = 1;
--- xen-unstable-10712/tools/ioemu/block-cow.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block-cow.c 2006-07-28 02:21:34.000000000
-0400
@@ -69,7 +69,7 @@
struct cow_header_v2 cow_header;
int64_t size;
- fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+ fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE | O_SYNC);
if (fd < 0) {
fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
if (fd < 0)
--- xen-unstable-10712/tools/ioemu/block-qcow.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block-qcow.c 2006-07-28 02:20:05.000000000
-0400
@@ -95,7 +95,7 @@
int fd, len, i, shift;
QCowHeader header;
- fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+ fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE | O_SYNC);
if (fd < 0) {
fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
if (fd < 0)
--- xen-unstable-10712/tools/ioemu/block-vmdk.c.osync 2006-07-28
02:15:56.000000000 -0400
+++ xen-unstable-10712/tools/ioemu/block-vmdk.c 2006-07-28 02:20:20.000000000
-0400
@@ -96,7 +96,7 @@
uint32_t magic;
int l1_size;
- fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
+ fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE | O_SYNC);
if (fd < 0) {
fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
if (fd < 0)
------------------------------------------------------------------------
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