From 453f9a1652629e5805995b165be2e634c8487139 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Fri, 2 Jul 2010 14:01:21 +0200 Subject: block: Fix early failure in multiwrite 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 --- block.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) (limited to 'block.c') diff --git a/block.c b/block.c index 9176decf3..e65971c91 100644 --- a/block.c +++ b/block.c @@ -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; } -- cgit v1.2.3