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From: | Peter Lieven |
Subject: | Re: [Qemu-devel] [PULL 33/42] block: return BDRV_BLOCK_ZERO past end of backing file |
Date: | Fri, 13 Sep 2013 09:33:51 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130804 Thunderbird/17.0.8 |
On 06.09.2013 17:39, Stefan Hajnoczi wrote:
From: Paolo Bonzini <address@hidden> If the sectors are unallocated and we are past the end of the backing file, they will read as zero. Signed-off-by: Paolo Bonzini <address@hidden> Signed-off-by: Stefan Hajnoczi <address@hidden> --- block.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/block.c b/block.c index aa9ec83..82bbd6c 100644 --- a/block.c +++ b/block.c @@ -3102,8 +3102,16 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs, return ret; }- if (!(ret & BDRV_BLOCK_DATA) && bdrv_has_zero_init(bs)) {- ret |= BDRV_BLOCK_ZERO; + if (!(ret & BDRV_BLOCK_DATA)) { + if (bdrv_has_zero_init(bs)) {
this should be bdi->discard_zeroes. bdrv_has_zero_init() does only give a valid result right after bdrv_create(). i currently working on extending bdi. I can send a patch for this if you agree.
+ ret |= BDRV_BLOCK_ZERO; + } else { + BlockDriverState *bs2 = bs->backing_hd;
this segfaults if there is no backing_hd. found while testing get_block_status with iscsi. paolo, is this the correct fix? @@ -3110,7 +3157,7 @@ static int64_t coroutine_fn bdrv_co_get_block_status(BlockDriverState *bs, if (!(ret & BDRV_BLOCK_DATA)) { if (bdrv_has_zero_init(bs)) { ret |= BDRV_BLOCK_ZERO; - } else { + } else if (bs->backing_hd) { BlockDriverState *bs2 = bs->backing_hd; int64_t length2 = bdrv_getlength(bs2); if (length2 >= 0 && sector_num >= (length2 >> BDRV_SECTOR_BITS)) {
+ int64_t length2 = bdrv_getlength(bs2); + if (length2 >= 0 && sector_num >= (length2 >> BDRV_SECTOR_BITS)) { + ret |= BDRV_BLOCK_ZERO; + } + } } return ret; }
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