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block: Fix early failure in multiwrite

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bdrv_aio_writev may call the callback immediately (and it will commonly do so
in error cases). Current code doesn't consider this. For details see the
comment added by this patch.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Kevin Wolf 2010-07-02 14:01:21 +02:00
parent c2abccecd9
commit 453f9a1652
1 changed files with 29 additions and 6 deletions
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35
block.c
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@ -2183,8 +2183,29 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
// Check for mergable requests
num_reqs = multiwrite_merge(bs, reqs, num_reqs, mcb);
// Run the aio requests
/*
* 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;
for (i = 0; i < num_reqs; i++) {
mcb->num_requests++;
acb = bdrv_aio_writev(bs, reqs[i].sector, reqs[i].qiov,
reqs[i].nb_sectors, multiwrite_cb, mcb);
@ -2192,22 +2213,24 @@ int bdrv_aio_multiwrite(BlockDriverState *bs, BlockRequest *reqs, int num_reqs)
// We can only fail the whole thing if no request has been
// submitted yet. Otherwise we'll wait for the submitted AIOs to
// complete and report the error in the callback.
if (mcb->num_requests == 0) {
reqs[i].error = -EIO;
if (i == 0) {
goto fail;
} else {
mcb->num_requests++;
multiwrite_cb(mcb, -EIO);
break;
}
} else {
mcb->num_requests++;
}
}
/* Complete the dummy request */
multiwrite_cb(mcb, 0);
return 0;
fail:
for (i = 0; i < mcb->num_callbacks; i++) {
reqs[i].error = -EIO;
}
qemu_free(mcb);
return -1;
}