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[Qemu-devel] [PULL 70/93] block: Don't use guest sector size for qemu_bl
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PULL 70/93] block: Don't use guest sector size for qemu_blockalign() |
Date: |
Fri, 24 Jan 2014 18:21:53 +0100 |
bs->buffer_alignment is set by the device emulation and contains the
logical block size of the guest device. This isn't something that the
block layer should know, and even less something to use for determining
the right alignment of buffers to be used for the host.
The new BlockLimits field opt_mem_alignment tells the qemu block layer
the optimal alignment to be used so that no bounce buffer must be used
in the driver.
This patch may change the buffer alignment from 4k to 512 for all
callers that used qemu_blockalign() with the top-level image format
BlockDriverState. The value was never propagated to other levels in the
tree, so in particular raw-posix never required anything else than 512.
While on disks with 4k sectors direct I/O requires a 4k alignment,
memory may still be okay when aligned to 512 byte boundaries. This is
what must have happened in practice, because otherwise this would
already have failed earlier. Therefore I don't expect regressions even
with this intermediate state. Later, raw-posix can implement the hook
and expose a different memory alignment requirement.
Signed-off-by: Kevin Wolf <address@hidden>
Reviewed-by: Wenchao Xia <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
---
block.c | 23 ++++++++++++++++++++---
include/block/block.h | 3 +++
include/block/block_int.h | 3 +++
3 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/block.c b/block.c
index 275d387..e5f214d 100644
--- a/block.c
+++ b/block.c
@@ -218,6 +218,16 @@ static void bdrv_io_limits_intercept(BlockDriverState *bs,
qemu_co_queue_next(&bs->throttled_reqs[is_write]);
}
+size_t bdrv_opt_mem_align(BlockDriverState *bs)
+{
+ if (!bs || !bs->drv) {
+ /* 4k should be on the safe side */
+ return 4096;
+ }
+
+ return bs->bl.opt_mem_alignment;
+}
+
/* check if the path starts with "<protocol>:" */
static int path_has_protocol(const char *path)
{
@@ -497,6 +507,9 @@ int bdrv_refresh_limits(BlockDriverState *bs)
if (bs->file) {
bdrv_refresh_limits(bs->file);
bs->bl.opt_transfer_length = bs->file->bl.opt_transfer_length;
+ bs->bl.opt_mem_alignment = bs->file->bl.opt_mem_alignment;
+ } else {
+ bs->bl.opt_mem_alignment = 512;
}
if (bs->backing_hd) {
@@ -504,6 +517,9 @@ int bdrv_refresh_limits(BlockDriverState *bs)
bs->bl.opt_transfer_length =
MAX(bs->bl.opt_transfer_length,
bs->backing_hd->bl.opt_transfer_length);
+ bs->bl.opt_mem_alignment =
+ MAX(bs->bl.opt_mem_alignment,
+ bs->backing_hd->bl.opt_mem_alignment);
}
/* Then let the driver override it */
@@ -4797,7 +4813,7 @@ void bdrv_set_buffer_alignment(BlockDriverState *bs, int
align)
void *qemu_blockalign(BlockDriverState *bs, size_t size)
{
- return qemu_memalign((bs && bs->buffer_alignment) ? bs->buffer_alignment :
512, size);
+ return qemu_memalign(bdrv_opt_mem_align(bs), size);
}
/*
@@ -4806,12 +4822,13 @@ void *qemu_blockalign(BlockDriverState *bs, size_t size)
bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
{
int i;
+ size_t alignment = bdrv_opt_mem_align(bs);
for (i = 0; i < qiov->niov; i++) {
- if ((uintptr_t) qiov->iov[i].iov_base % bs->buffer_alignment) {
+ if ((uintptr_t) qiov->iov[i].iov_base % alignment) {
return false;
}
- if (qiov->iov[i].iov_len % bs->buffer_alignment) {
+ if (qiov->iov[i].iov_len % alignment) {
return false;
}
}
diff --git a/include/block/block.h b/include/block/block.h
index 00a8790..332ebb9 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -428,6 +428,9 @@ void bdrv_img_create(const char *filename, const char *fmt,
char *options, uint64_t img_size, int flags,
Error **errp, bool quiet);
+/* Returns the alignment in bytes that is required so that no bounce buffer
+ * is required throughout the stack */
+size_t bdrv_opt_mem_align(BlockDriverState *bs);
void bdrv_set_buffer_alignment(BlockDriverState *bs, int align);
void *qemu_blockalign(BlockDriverState *bs, size_t size);
bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index f6fa1f6..74a78a6 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -258,6 +258,9 @@ typedef struct BlockLimits {
/* optimal transfer length in sectors */
int opt_transfer_length;
+
+ /* memory alignment so that no bounce buffer is needed */
+ size_t opt_mem_alignment;
} BlockLimits;
/*
--
1.8.1.4
- [Qemu-devel] [PULL 53/93] block: Add bs->node_name to hold the name of a bs node of the bs graph., (continued)
- [Qemu-devel] [PULL 53/93] block: Add bs->node_name to hold the name of a bs node of the bs graph., Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 61/93] block: resize backing file image during offline commit, if necessary, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 62/93] block: resize backing image during active layer commit, if needed, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 64/93] block: Fix bdrv_commit return value, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 63/93] block: update block commit documentation regarding image truncation, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 65/93] block: Move initialisation of BlockLimits to bdrv_refresh_limits(), Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 66/93] block: Inherit opt_transfer_length, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 68/93] qemu_memalign: Allow small alignments, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 67/93] block: Update BlockLimits when they might have changed, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 69/93] block: Detect unaligned length in bdrv_qiov_is_aligned(), Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 70/93] block: Don't use guest sector size for qemu_blockalign(),
Kevin Wolf <=
- [Qemu-devel] [PULL 71/93] block: rename buffer_alignment to guest_block_size, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 72/93] raw: Probe required direct I/O alignment, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 76/93] block: write: Handle COR dependency after I/O throttling, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 77/93] block: Introduce bdrv_co_do_pwritev(), Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 78/93] block: Switch BdrvTrackedRequest to byte granularity, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 79/93] block: Allow waiting for overlapping requests between begin/end, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 80/93] block: Make zero-after-EOF work with larger alignment, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 81/93] block: Generalise and optimise COR serialisation, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 82/93] block: Make overlap range for serialisation dynamic, Kevin Wolf, 2014/01/24
- [Qemu-devel] [PULL 83/93] block: Allow wait_serialising_requests() at any point, Kevin Wolf, 2014/01/24