From 339064d5063924e5176842abbf6c8089f3479c5b Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Thu, 28 Nov 2013 10:23:32 +0100 Subject: block: Don't use guest sector size for qemu_blockalign() 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 Reviewed-by: Wenchao Xia Reviewed-by: Max Reitz --- block.c | 23 ++++++++++++++++++++--- 1 file changed, 20 insertions(+), 3 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index 275d387354..e5f214d135 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 ":" */ 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; } } -- cgit v1.2.3