[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH] vpc: Implement bdrv_co_get_status()
From: |
Max Reitz |
Subject: |
Re: [Qemu-devel] [PATCH] vpc: Implement bdrv_co_get_status() |
Date: |
Wed, 11 Feb 2015 17:51:38 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 |
On 2015-02-11 at 11:23, Kevin Wolf wrote:
This implements bdrv_co_get_status() for VHD images. This can
significantly speed up qemu-img convert operation because only with this
function implemented sparseness can be considered. (Before, converting a
1 TB empty image took several minutes for me, now it's instantaneous.)
Signed-off-by: Kevin Wolf <address@hidden>
---
block/vpc.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 52 insertions(+), 2 deletions(-)
diff --git a/block/vpc.c b/block/vpc.c
index 46803b1..379ff4a 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -597,6 +597,55 @@ static coroutine_fn int vpc_co_write(BlockDriverState *bs,
int64_t sector_num,
return ret;
}
+static int64_t coroutine_fn vpc_co_get_block_status(BlockDriverState *bs,
+ int64_t sector_num, int nb_sectors, int *pnum)
+{
+ BDRVVPCState *s = bs->opaque;
+ VHDFooter *footer = (VHDFooter *) s->footer_buf;
Double space before the left parenthesis.
+ int64_t start, offset;
+ bool allocated;
+ int n;
+
+ if (be32_to_cpu(footer->type) == VHD_FIXED) {
+ *pnum = nb_sectors;
+ return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_DATA |
+ (sector_num << BDRV_SECTOR_BITS);
+ }
+
+ offset = get_sector_offset(bs, sector_num, 0);
+
+ *pnum = 1;
+ start = offset;
+ allocated = (offset != -1);
+ nb_sectors--;
+
+ while (nb_sectors > 0) {
+ offset = get_sector_offset(bs, sector_num, 0);
During the first iteration, this will is exactly the function call as
the one before this loop.
+
+ if ((offset != -1) != allocated) {
+ break;
+ }
+
+ if (allocated && offset != start + (*pnum * 512)) {
Therefore, if allocated is true, this check will always fail because
offset == start.
+ break;
+ }
+
+ /* All sectors in a block are contiguous (without using the bitmap) */
+ n = ROUND_UP(sector_num + 1, s->block_size / 512) - sector_num;
+ n = MIN(n, nb_sectors);
I think you can make use of this assumption even before calling
get_sector_offset() in the first iteration.
Also, 512 is shorter than BDRV_SECTOR_SIZE and it's nice to get it on a
single line, but I think not introducing another literal 512 in the code
would be nicer; the same applies above in "*pnum * 512".
Max
+
+ *pnum += n;
+ sector_num += n;
+ nb_sectors -= n;
+ }
+
+ if (allocated) {
+ return BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start;
+ } else {
+ return 0;
+ }
+}
+
/*
* Calculates the number of cylinders, heads and sectors per cylinder
* based on a given number of sectors. This is the algorithm described
@@ -907,8 +956,9 @@ static BlockDriver bdrv_vpc = {
.bdrv_reopen_prepare = vpc_reopen_prepare,
.bdrv_create = vpc_create,
- .bdrv_read = vpc_co_read,
- .bdrv_write = vpc_co_write,
+ .bdrv_read = vpc_co_read,
+ .bdrv_write = vpc_co_write,
+ .bdrv_co_get_block_status = vpc_co_get_block_status,
.bdrv_get_info = vpc_get_info,