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block: simplify failure handling for bdrv_aio_multiwrite 

Now that early failure of bdrv_aio_writev is not possible anymore,
mcb->num_requests can be set before the loop starts.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Paolo Bonzini 2011-11-14 17:50:50 +01:00 committed by Kevin Wolf
parent ad54ae80c7
commit df9309fb43
1 changed files with 2 additions and 26 deletions
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28
block.c
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@ -2842,37 +2842,13 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
trace_bdrv_aio_multiwrite(mcb, mcb->num_callbacks, num_reqs);
/*
* Run the aio requests. As soon as one request can't be submitted
* successfully, fail all requests that are not yet submitted (we must
* return failure for all requests anyway)
*
* num_requests cannot be set to the right value immediately: If
* bdrv_aio_writev fails for some request, num_requests would be too high
* and therefore multiwrite_cb() would never recognize the multiwrite
* request as completed. We also cannot use the loop variable i to set it
* when the first request fails because the callback may already have been
* called for previously submitted requests. Thus, num_requests must be
* incremented for each request that is submitted.
*
* The problem that callbacks may be called early also means that we need
* to take care that num_requests doesn't become 0 before all requests are
* submitted - multiwrite_cb() would consider the multiwrite request
* completed. A dummy request that is "completed" by a manual call to
* multiwrite_cb() takes care of this.
*/
mcb->num_requests = 1;
// Run the aio requests
/* Run the aio requests. */
mcb->num_requests = num_reqs;
for (i = 0; i < num_reqs; i++) {
mcb->num_requests++;
bdrv_aio_writev(bs, reqs[i].sector, reqs[i].qiov,
reqs[i].nb_sectors, multiwrite_cb, mcb);
}
/* Complete the dummy request */
multiwrite_cb(mcb, 0);
return 0;
}